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Students get through AP Inter 2nd Year Chemistry Important Questions Lesson 6(b) Group-16 Elements which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions Lesson 6(b) Group-16 Elements

Very Short Answer Questions

question 1.
Write any two compounds, in which oxygen shows an oxidation state different from -2. Give the oxidation states of oxygen in them.
Answer:
OF₂ and O₂ F₂ are two compounds in which oxygen shows an oxidation state different from -2.

• In OF₂ the oxidation state of oxygen is +2.
• In O₂F₂ the oxidation state of oxygen is +1.

Question 2.
Why H₂O a liquid while H₂S Is a gas? ( IPE May – 2014)
Answer:
H₂O is liquid due to the presence of intermolecular hydrogen bonding. While H₂S is gas because it is not having such type of bonding.

Question 3.
H₂O is neutral while H₂S is acidic — explain.
Answer:
H₂O is neutral while H₂S is acidic.
Reason: The O-H bond dissociation enthalpy is greater than the S — H bond dissociation enthalpy.

Question 4.
Explain the structures of SF₄ and SF₆.
Answer:
Structure of SF₄:

• In SF₄ ‘S’ undergoes sp³d hybridisation.
• It has trigonal bipyramidal structure in which one of the equitorial positions is occupied by a lone pair of electrons. This geometry is also known as see – saw geometry.
  Structure of SF₆:
• In SF₆, ‘S’ undergoes sp³d² hybridisation,
• It has octahedral structure.

Question 5.
Give one example each for
a) a neutral oxide
b) a peroxide
c) a super oxide
Answer:
a) CO, N₂O are neutral oxides.
b) Na₂O₂, BaO₂ are peroxides.
c) KO₂, RhO₂ are super oxides.

Question 6.
What is tailing of mercury? How is it removed? (IPE Mar – 2015 (TS))
Answer:
Mercury loses it’s lustreness, meniscus and consequently sticks to the walls of glass vessel when it reacts with ozone. This phenomenon is called tailing of mercury
2Hg + O₃ → Hg₂O + O₂
It is removed by shaking it with water which dissolves Hg₂O.

Question 7.
How does ozone react with Ethylene?
Answer:
Ethylene reacts with ozone to form Ethylene ozonoid followed by the hydrolysis to form formaldehyde.

Question 8.
Which form of sulphur shows paramagnetism?
Answer:
In vapour state sulphur partly exists as S₂ molecule which has two unpaired electrons in the antibonding π (π*)orbitals like O₂. Hence it exhibits paramagnetism.

Question 9.
Why are group — 16 elements called chalçogens ?
Answer:
Chalcogens means mineral forming (or) ore forming elements. Most of elements exist in earth crust as oxides, sulphides, selinides, telurids etc. So Group – 16 elements are called as chalcogens.

Question 10.
Write any two uses each for O₃ and H₂SO₄.
Answer:
Uses of O₃:

• Ozone is used in sterilisation of water.
• Ozone is used in manufacture of artificial silk and camphor etc.
• Ozone is used to identify unsaturation in carbon compounds.

Uses of H₂SO₄:

• H₂SO₄ is used in the manufacture of fertilisers.
• H₂SO₄ is used in petrol refining.
• H₂SO₄ is used in detergent industry.

Short Answer Questions

Question 1.
Write a. short note on the allotropy of sulphur.
Answer:
The important allotropes of sulphur are
a) yellow rhombic (α. sulphur).
b) Monoclinic (β – sulphur).

The stable from is α-sulphur (at room temperature).
Rhombic sulphur (α – Sulphur):

• Colour : Yellow.
• Melting point : 3858K.
• Specific gravity: 2.06.
• It is insoluble in water and partially soluble in alcohol, benzene etc., and readily soluble in CS₂.

Monoclinic sulphur (β – Sulphur):

• Melting point: 392K
• Specific gravity: 1.98.
• It is soluble in Cs₂.
• Rhombic sulphur transforms to monoclinic sulphur by heating above 369K. This temperature is called transition temperature.

Question 2.
Which is used for drying ammonia?
Answer:
For drying ammonia quick lime (CaO) is used.

• For drying ammonia conc. H₂SO₄ , P₄O₁₀ and anhydrous CaCl₂ cannot be used because they react with ammonia and forms (NH₄)₂SO₄, (NH₄)₃PO₄ and CaCl₂. 8NH₃

Question 3.
Explain the conditions favourable for the formation of SO₃ from SO₂ in the contact process of H₂SO₄.
Answer:
Le Chatlier’s principle — Application to produce SO₃:
The oxidation of SO₂ to SO₃ in the presence of a catalyst is a reversible reaction. The thermochemical equation for the conversion is written as

The equation reveals the following points:

1. 3 volumes of the reactants convert into 2 volumes of SO₃. i.e., a decrease of volume accompanies the reaction.
2. the reaction is an exothermic change.
3. the catalyst may be present to increase the SO₃ yields.

According to Le Chattier’s principle,

i. a decrêase in volume of the system is favoured at high pressures. But in practice only about 2 bar pressure is used. The reason for not using high pressures is acid resisting towers which can withstand high pressures cannot be built.

ii. exothermic changes are favoured at low temperatures. It is not always convenient in the industry to work at low temperatures. In such situations an optimum temperature is maintained. At this temperature considerable amounts of the product are obtained, in the manufacture of H₂SO₄, the optimum temperature suitable for the conversion of SO₂ into SO₃ is experimentally found to be 720K.

iii. The rate of formation of SO₃ is enhanced by the use of a catalyst. (V₂O₅ (or) Pt – asbestos).
Favourable Conditions:
Temperature: 720K
Pressure :2 bar
Catalyst : V₂O₅ (or) platinized asbestos.

Question 4.
Which oxide of sulphur can act as both oxidizing and reducing agent? Give one example each.
Answer:
Sulphur dioxide (SO₂) acts as both oxidising as well as reducing agent.
SO₂ as Oxidising agent:
Sodium sulphide oxidises to hypo with SO₂.
2Na₂S + 3SO₂ → 2Na₂S₂O₃ + S
SO₂ as Reducing agent:
SO₂ reduces Fe⁺³ ions to Fe⁺² ions.
2Fe⁺³ + SO₂ + 2H₂O → 2Fe²⁺ + \(\mathrm{SO}_4^{-2}\) + 4H⁺

Long Answer Questions

Question 1.
Explain in detail the manufacture of sulphuric acid by contact process. ( IPE 2016 (TS))
Answer:
Manufacture of H₂SO₄ by contact process:
Manufacturing of H₂SO₄ involves three main steps.

Step-I:
SO₂ production : The required SO₂ for this process is obtained by burning S(or) Iron
pyrites in oxygen.
S + O₂ → SO₂
4FeS₂ + 15O₂ → 2Fe₂O₃ + 8SO₃

Step—2
SO₃ formation: SO₂ is oxidised in presence of catalyst with atmospheric air to form SO₃.

Le Chatliers principle — Application to produce SO₃ ;
The oxidation of SO₂ to SO₃ in the presence of a catalyst is a reversible reaction. The
thermochemical equation for the conversion is written as

The equation reveals the following points:

1. 3 volumes of the reactants convert into 2 volumes of SO₃. i.e., a decrease of volume accompanies the reaction.
2. The reaction is an exothermic change.
3. The catalyst may be present to increase the SO₃ yields.

According to Le Chatlier’s principle,

1. a decrease in volume of the system is favoured at high pressures. But in practice only about 2 bar pressure is used. The reason for not using high pressures is acid resisting towers which can withstand high pressures cannot be built.
2. exothermic changes are favoured at low temperatures. It is not always convenient in the industry to work at low temperatures. in such situations an optimum temperature is maintained. At this temperature considerable amounts of the product are obtained. In the manufacture of H₂SO₄, the optimum temperature suitable for the conversion of SO₂ into SO₃ is experimentally found to be 720K.
3. The rate of formation of SO₃ is enhanced by the use of a catalyst. (V₂ O₅ (or) Pt – asbestos).
   Favourable Conditions:
   Temperature: 720K :
   Pressure : 2 bar
   Catalyst : V₂O₅ (or) platinized asbestos.
   

Step-3

• Formation of H₂SO₄: SO₃ formed in the above step absorbed in 98% H₂SO₄ to get oleum (H₂S₂O₇). This oleum is diluted to get desired concentration of H₂SO₄.
  SO₃ + H₂SO₄ → H₂S₂O₇
  H₂S₂O₇ + H₂O → H₂SO₄

Question 2.
How is ozone prepared from oxygen? Explain its reaction with
a) C₂H₄
b) KI
c) Hg
d) PbS. (T.S. & A.P. Mar. ’17) (A.P.Mar. ’16) (Mar. ’14)
Answer:
Preparation of Ozone:
A slow dry stream of oxygen under silent electric discharge to form ozone (about 10%). The product obtained is known as ozonised oxygen.
3O₂ → 2O₃ ΔH° = 142kJ/mole .

• The formation of ozone is an endothermic reaction.
• It is necessary to use silent electric discharge in the preparation of O₃ to prevent its decomposition

a) Reaction with C₂H₄ : Ethylene reacts with ozone to form Ethylene ozonoid followed by the hydrolysis to for formaldehyde.

b) Reaction with KI : Moist KI is oxidised to Iodine in presence of ozone.
2KI + H₂O + O₃ → 2KOH + I₂ + O₂
c) Reaction with Hg: Mercury loses it’s lustreness, meniscus and consequently sticks to the walls of glass vessel when it reacts with ozone. This phenomenon is called tailing of mercury.
2Hg + O₃ → Hg₂O + O₂
It is removed by shaking it with water which dissolves Hg₂O.
d) Reaction with PbS : Black lead sulphide oxidised to white lead sulphate in presence of ozone.
PbS + 4O₃ → PbSO₄ + 4O₂.

Question 3.
Write the structures of oxoacids of sulphur. (IPE 2016 (TS))
Answer:
Oxoacids of sulphur: Sulphur forms a number of oxoacids such as H₂SO₃. H₂S₂O₃, H₂S₂O₄, H₂S₂O₅, H₂S₂O₆ (x = 2 to 5), H₂SO₄, H₂S₂O₇, H₂SO₅, H₂S₂O₈.

Question 4.
Write any two oxidation and any two reduction properties of ozone with equations.
Answer:
Oxidation properties:

1. Ozone oxidises moist potassium idodide and liberates I₂.
   2KI + H₂O + O₃ → 2KOH + I₂ + O₂
2. Ozone oxidises black lead sulphide to white lead sulphate. PbS + 4O₃ → PbSO₄ + 4O₂

Reduction properties:

1. Ozone reduces H₂O₂ to H₂O.        H₂O₂ + O₃ → H₂O + 2O₂
2. Ozone reduces Ag₂O to Ag.         Ag₂O + O₃ → 2Ag + 2O₂

Students get through AP Inter 2nd Year Chemistry Important Questions 5th Lesson General Principles of Metallurgy which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions 5th Lesson General Principles of Metallurgy

Very Short Answer Questions

Question 1.
What is the role of depressant in froth floatation?
Answer:
By using depressants in froth floatation process, it is possible to separate a mixture of two sulphide ores.
Eg: In the ore containing ZnS and PbS, the depressant used is NaCN. It prevents ZnS from coming to the froth but allows PbS to come with the froth.

Question 2.
Explain “poling”. (AP Mar. ’16, ’15; IPE ’16, 15 (AP))
Answer:
When the metals are having the metal oxides as impurities this method is employed. The impure metal is. melted and is then covered by carbon powder. Then it is stirred with green wood poles. The reducing gases formed from the green wood and the carbon, reduce the oxides to the metal.
Eg : Cu & Sn metals are refined by this method.

Question 3.
Decribe a method for the refining of nickel.
Answer:
Mond’s process:

• In Mond’s process, nickel is heated in a stream of carbon monoxide forming a volatile complex, nickel tetra carbonyl.
  
• Nickel tetra carbonyl is strongly heated to decompose and gives the pure Nickel.
  

Question 4.
What is the role of cryolite in the metallurgy of aluminium ? (IPE 2015 (TS), BMP, 2016 (TS))
Answer:
By adding the cryolite to the pure Alumina, the melting point of pure Alumina is lowered (which is very high 2324K) and electrical conductivity of pure alumina is increased.

Question 5.
Give the composition of the following alloys (IPE ’16, ’14 (TS)) (AP & TS Mar. ’17)
a) Brass
b) Bronze
c) German Silver
Answer:
a) Composition of Brass : 60 – 80% Cu, 20 – 40% Zn
b) Composition of Bronze : 75 – 90% Cu, 10 – 25% Sn
c) Composition of German silver : 50 – 60% Cu, 10 – 30% Ni, 20 – 30% Zn.

Question 6.
What is matte ? Give its composition.
Answer:
During the extraction of ’Cu’ from copper pyrites the product of the blast furnace consists mostly of Cu₂S and a little of FeS. This product is known as “Matte”. It is collected from the outlet at the bottom of the furnace.

Question 7.
What is flux ? Give an example.
Answer:
Flux : An outside substance added to. ore to lower its melting point is known as flux.

• Flux combines with gangue and forms easily fusible slag.
  gangue + flux → slag
  

Question 8.
How is aluminium useful in the extraction of chromium and manganese from their oxides ?
Answer:

• ‘Al’ is used as reducing agent.
• By Alumino thermite process Cr, Mn are extracted from their oxides.
• The reactions are highly exothermic.

Cr₂O₃ + 2Al → 2Cr + Al₂O₃
3Mn₃O₄ + 8Al → 4Al₂O₃ + 9Mn

Question 9.
What is a mineral ?
Answer:
The chemical compound from which a metal can be extracted is called a mineral. Bauxite, crayolite are the minerals of aluminium.

Question 10.
What is an ore ?
Answer:
An ore is a mineral from which the metal can be extracted easily and economically. Bauxite is the ore of aluminium.

Question 11.
What is a ore. Give the ores of Al, Zn, Fe, Cu.
Answer:
The mineral from which metal can be extracted economically is called ore.
Aluminium ores : Bauxite = Al₂ O₃. 2H₂O; Cryolite = Na₃Al F₆
Zinc ores : Zinc blende = Zns; Calamine = ZnCO₃
Copper ores : Cuprite: CuO; Copper pyrites = Cu₂S
Iron ores : Haematite = Fe₂O₃ Magnetite = Fe₃O₄

Question 12.
What is the role of SiO₂ in the extraction of copper.
Answer:
In the extraction of copper SiO₂ acts as flux. It combines with FeO and removes as slag.
FeO + SiO₂ (flux) → FeSiO₃ (Slag)

Short Answer Questions

Question 1.
Outline the principles of refining of metals by the following methods.
(a) Zone refining
(b) Electrolytic refining
(c) Poling
(d) Vapour phase refining.
Answer:
a) Zone refining :

• Zone refining is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal.
• A circular mobile heater is fixed at one end of a rod of impure metal.
• The molten zone moves along with the heater moves forward the pure metal crystallises out of the melt and the impurities pass into the adjacent molten zone.

• The above process is repeated several times and the heater is moved in the same direction form one end to the other end. At one end impurities get concentrated. This end is cut off.
• This method is very useful for producing semiconductor grade metals of very high purity.
  Eg : Ge, Si, B, Ga etc…

b) Electrolytic refining: This process is used for less reactive metals like Cu, Ag, AZ, Au etc.

• In this process anode is made by impure metal and a thin strip of pure metal acts as cathode.
• On electrolysis metal dissolves from anode and pure metal gets deposited at cathode.

Impurities settle down below anode in the form of anode mud.

c) Poling : When the metals are having the metal oxides as impurities this method is employed. The impure metal is melted and is then covered by carbon powder. Then it is stirred with green wood poles. The reducing gases formed from the green wood and the carbon, reduce the oxides to the metal. Eg : Cu & Sn metals are refined by this method.

d) Vapour phase refining: In this method the metal is converted into its volatile compound and coll Ted. It is then decomposed to give pure metal.

1. The metal should form a volatile compound with an available reagent.
2. The volatile compound should be easily decomposable. So the recovery is easy.
   E.g : Mond’s process :
   • In Mond’s process, nickel is heated in a stream of carbon monoxide forming a volatile complex, nickel tetra carbonyl,
     
   • Nickel tetra carbonyl is strongly heated to decompose and gives the pure Nickel.
     

Question 2.
Explain the purification of sulphide ore by froth floatation method. (Mar ’15) (A.P. Mar. ’17)
Answer:
Froth floatation method :

• This method is used to concentrate sulphide ores.
• In this process a suspension of the powdered ore is made with water.
• A rotating paddle is used to agitate the suspension and air is blown into the suspension in presence of an oil.
• Froth is formed as a result of blown of air, which carries the mineral particles.
  
• To the above slurry froth collectors and stabilizers are added.
• Collectors like pine oil enhance non-wettability of the mineral particles.
• Froth stabilizers like cresol stabilize the froth.
• The mineral particles wet by oil and gangue particles wet by water.
• The broth is light and is skimmed off. The ore particles are then obtained from the froth. By using depressants in froth floatation process, it is possible to separate a mixture of two suplhide ores. Eg: In the ore containing ZnS and PbS, the depressant used is NaCN. It prevents ZnS from coming to the froth but allows PbS to come with the froth.

Question 3.
What is Ellingham diagram ? What information can be known from this in the reduction of oxides ?
Answer:
The graphical representation of Gibbs energy which provides a sound basis for considering the choice of reducing agent in the reduction of oxides. This graphical representation is known as Ellingham diagram.
This diagram helps us in predicting the feasibility of thermal reduction of an ore.

• The Criterion of feasibility of a reaction is that at a given temperature, Gibbs energy of the reaction must be negative.
• Ellingham diagram normally consists plots of ΔG° vs T for formation of oxides of elements.
• The graph indicates whether a reaction is possible or not, i.e., the tendency of reduction with a reducing agent is indicated.
• The reducing agent forms its oxide when the metal oxide is reduced. The role of reducing agent is to make the sum of ΔG° values of the two reactions negative.
• Out of C and CO, Carbon monoxide (CO) is a better reducing agent at 673K.
• At 983K (or) above coke(C) is better reducing agent.
• The above observations are from Ellingham diagram.
  Zinc is not extracted from zinc oxide through reduction by using CO.

Explanation :
2Zn + O₂ → 2ZnO, ΔG° = -650 kJ
2CO + O₂ → 2CO₂, ΔG° = -450 kJ
2ZnO + 2CO → 2Zn, 2CO₂, ΔG° = 200 kJ
ΔG° = Positive indicates that the reaction is not feasible.
The above fact is explained on the basis of Ellingham diagram.

Question 4.
Give examples to differentiate roasting and calcination. (IPE ’14, B.M.P. 2016) (A.P. & T.S. Mar. ’16, ’15)
Answer:
Roasting: Removal of the volatile components of a mineral by heating mineral either alone (or) mixed with some other substances to a high temperature in the presence of air is called Roasting.

• It is applied to the sulphide ores.
• SO₂ gas is producted along with metal oxide.
  

Calcination: Removed of the volatile components of a mineral by heating in the absence of air is called calcination.

• It is applied to carbonates and bicarbonates.
• CO₂ gas is produced along with metal oxide.

Question 5.
How is copper extracted from copper pyrites ?
Answer:
Extraction of copper from copper pyrites :
Copper pyrite is the main source of copper metal. Various steps involved in the extraction of copper are discussed below.

Step -I:

Concentration of ore by froth floatation process :
The ore is first crushed in ball mills. The finely divided ore is suspended in water. A little pine oil is added and the mixture is vigorously’ agitated by a current of air. The froth formed carries the ore particles almost completely. The gangue sinks to the bottom of the tank. The froth is separated and about 95% concentrated ore is obtained.

Step -II:

Roasting : To remove the volatile impurities like As (or) Sb, the ore is roasted in a free supply of air. A mixture of sulphides of copper and iron are obtained and these are partially oxidised to respective oxides.
Cu₂S. Fe₂S₃ + O₂ → Cu₂S + 2FeS + SO₂
2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
2FeS + 3O₂ → 2FeO + 2SO₂

Step -III: .

The roasted ore is mixed with a little coke and sand (Silica) and smelted in a blast furnace and fused. A blast of air, necessary for the combustion of coke, is blown through the tuyeres present at the base of the furnace.’ The oxidation of the sulphides of copper and iron will be completed further. A slag of iron silicate is formed according to the reactions given below :

Step -IV :

After smelting the copper ore in blast furnace, the product of the blast furnace consists mostly of Cu₂S and a little of ferrous sulphide. This product is known as “Matte.” It is collected from the outlet at the bottom of the furnace. After then the following processes are carried out for getting the pure copper.

Bessemerization : The matte is charged into a Bessemer converter. A bessemer converter is a pear-shaped furnace. It is made of steel plates. The furnace is given a basic lining with lime or magnesium oxide (obtained from dolomite or magnesite). The converter is held in position by trunnions and can be tilted in any position. A hot blast of air and sand is blown through the tuyeres present near the bottom. Molten metal, the product in the furnace, collects at the bottom of the converter.

Reactions that took place in blast furnace go to completion. Almost all of iron is eliminated slag. Cuprous oxide combines with cuprous sulphide and forms Cu metal.
2Cu₂O + Cu₂S → 6Cu + SO₂
The molten metal is cooled in sand moulds. SO₂ escapes. The impure copper metal is known as ‘Blister copper” and is about 98% pure.

Step -V:

Refining: The Blister copper is purified by electrolysis. The impure copper metal is made into plates. They are
suspended into lead — lined tanks containing Copper (II) Sulphate solution. Thin plates of pure copper serve as
cathode. The cathode plates are coated with graphite. On electrolysis, pure copper is deposited at the cathode. The
copper obtained is almost 100% pure Cu.

Question 6.
Explain the process of leacing of aluminium from bauxite.
Answer:
Extraction of Aluminium from Bauxite:
For the purpose of extraction of Al, Bauxite is the best source.
Purification of Bauxite: Bauxite containing Fe₂O₃ as impurity is known as Red Bauxite.
Bauxite containing SiO₂ as impurity is known as White Bauxite and can be purified by “Set-peck’s Process. Red Bauxite is purified by Bayer’s process and Hall’s process.

Bayer’s Process: Red bauxite is roasted and digested in concentrated NaOH at 423 K. Bauxite dissolves in NaOH to form sodium meta aluminate while impurity Fe₂O₃ does not dissolve which can be removed by filtration.
Al₂O₃.2H₂O + 2NaOH → 2NaAlO₂ + 3H₂O
The solution which contains sodium meta aluminate is diluted and crystals of Al(OH)₃, are added which serves as seeding orgent. Sodium meta aluminate undergoes hydrolysis to precipitate Al(OH)₃.
2NaAlO₂ + 4H₂O → 2NaOH + 2Al(OH)₃↓
Al(OH)₃ is filtered and ignited at 1200°C to get anhydrous alumina.

Halls’ Process: Red Bauxite is fused with sodium carbonate to form sodium meta aluminate
which is extracted with water. The impurity Fe₂O₃ is filtered out.
Al₂O₃ + Na₂CO₃ → 2NaAlO₂ + CO₂
Into the solution of sodium meta aluminate, CO₂ gas is passed to precipitate Al(OH)₃.

The precipitated Al(OH)₃ is ignited at 1200°C to get anhydrous alumina.
2Al(OH)₃ → Al₂O₃ + 3H₂O

Serpeck’s Process: Powdered bauxite is mixed with coke and heated to 2075 K in a current of nitrogen gas. Aluminium Nitride is formed while SiO₂ is reduced to Si which escapes out.

Aluminium nitride is hydrolysed to get aluminium hydroxide which on ignition gives anhydrous alumina.

Electrolytic Reduction of Alumina: Pure Alumina (Al₂O₃) is a bad conductor of electricity and it has high melting point (2050°C). So it cannot be electrolysed. Alumina is electrolysed by dissolving in fused cryolite to increase the conductivity and small amount of Fluorspar is added to reduce its melting point. Thus the electrolyte is a fused mixture of Alumina, Cryolite and Fluorspar.

Electrolysis is carried out in an iron tank lined inside with graphite (carbon) which functions as cathode. A number of carbon rods (or) copper rods suspended in the electrolyte functions as anode.

An electric current of 100 amperes at 6 to 7 volts is passed through the electrolyte. Heat produced by the current keeps the mass in fused state at 1175 to 1225K. The following reactions take place in the electrolytic cell under these conditions.
Na₃AlF₆ → 3NaF + AlF₃
Cryolite
4AlF₃ → 4Al³⁺ + 12F^–
At cathode : 4Al³⁺ + 12e^– → 4Al
At anode : 12F^– → 6F₂ + 12e^–
F₂ formed at the anode reacts with alumina and forms Aluminium fluoride.
2Al₂O₃ + 6F₂ → 4AlF₃ + 3O₂
Aluminium, produced at the cathode, sinks to the bottom of the cell. It is removed from time to time through topping hole.

Purification of Aluminium: (Hoope’s Process)

The impurities present are Si, Cu, Mn etc.,
The electrolytic cell used for refining of aluminium consists of iron tank lined inside with
carbon. This acts as anode. The tank contains three layers of fused masses. The bottom layer
contains impure aluminium. Middle layer contains mixture of AlF₃, NaF and BaF₂ saturated with Al₂O₃. Top layer contains pure aluminium and graphite rods kept in it act as cathode.

On passing current aluminium ions from the middle layer are discharged at the cathode as pure aluminium. Equivalent amount of aluminium from the bottom layer passes into middle layer.

Question 7.
Explain the reactions occuring in the blast furnace in the extraction of iron.
Answer:
In the Blast furnace, reduction of iron oxides takes place in different temperature ranges. Hot air is blown from the bottom of the furnace and coke is burnt to give temperature upto about 2200K in the lower portion itself, The burning of coke therfore supplies most of the heat required in the process. The CO and heat moves to upper part of the furnace. In upper part, the temperature is lower and the iron oxides (Fe₂O₃ and Fe₃O₄) coming from the top are reduced in steps to FeO. Thus, the reduction reactions taking place in the lower temperature range and in the higher temperature range, depend on the points of corresponding intersections in the Δ_rG^θ vs T plots. These reactions can be summarised as follows:

At 500 — 800 K (lower temperature range in the blast furnace)
3 Fe₂O₃ + CO → 2 Fe₃O₄ + CO₂
Fe₃O₄ + 4CO → 3 Fe + 4 CO₂.
Fe₂O₃ + CO → 2 FeO + CO₂
At 900- 1500 K (higher temperature range in the blast furnace)
C + CO₂ → 2 CO
FeO + CO → Fe + CO₂
Lime stone is also decomposed to CaO which removes silicate impurity of the ore as CaSiO₃ slag. The slag is in molten state and separåtes out from iron.

The iron obtained from blast furnace contains about 4% carbon and many impurities in smaller amount (e.g., S, P, Si, Mn). This is known as pig iron. Cast iron is different from and is made by melting pig iron with scrap iron and coke using hot air blast. It has slightly lower carbon content (about 3%) and is extremely hard and brittle.
Fe₂O₃ + 3 C → 2 Fe + 3 CO

Students get through AP Inter 2nd Year Chemistry Important Questions 4th Lesson Surface Chemistry which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions 4th Lesson Surface Chemistry

Very Short Answer Questions

Question 1.
What is adsorption ? Give one example.
Answer:
Adsorption : The accumulation (or) concentration of a substance on the surface rather than in the bulk of solid (or) liquid is known as adsorption.
Eg : Adsorption of gases like O₂, H₂, Cl₂ etc., on charcoal.

Question 2.
What is absorption ? Give one example.
Answer:
Absorption : The uniform distribution of a substance through out the bulk of the solid substance is known as absorption.
Eg : Chalk stick dipped in ink.

Question 3.
What is desorption ?
Answer:
Desorption : The process of removing an adsorbed substance from a surface on which it is adsorbed is called desorption.

Question 4.
What is sorption ? (or) What is the name given to the phenomenon when both absorption and adsorption take place together ?
Answer:
The process in which both adsorption and absorption takes place simultaneously is called sorption.

Question 5.
Give any two applications of adsorption.
Answer:
Applications of adsorption :
a) Separation of inert gases : Different noble gases adsorb at different temperatures on coconut charcoal. By this principle (adsorptipn) mixture of noble gas is separated by adsorption on coconut charcoal.

b) Gas masks : Gas mask is a device which consists of activated charcoal (or) mixture of adsorbents is used by coal miners to adsorb poisonous gases during breathing.

Question 6.
What is an adsorption isotherm ? Write the equation of Freundlich adsorption isotherm.
Answer:
Adsorption Isotherm : The variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature can be expressed by means of a curve known as adsorption isotherm.

• Freundlich adsorption isotherm equation is \(\frac{\mathrm{x}}{\mathrm{m}}\) = k. P^1/n
  x = mass of the gas adsorbed
  m = mass of the adsorbent
  P, k and n are constants.

Question 7.
Define “promoters” and “poisons” in the phenomenon of catalysis. ‘
Answer:
Promoters: The substances which enhance the activity of catalyst are known as promoters.
Poisons : The substances which decrease the activity of a catalyst are known as poisons.

Question 8.
What is homogeneous catalysis ? How is it different from heterogeneous catalysis ?
Answer:
Homogeneous Catalysis : The catalysis in which reactants and catalyst are in same phase is called Homogeneous catalysis.

• In case of heterogeneous catalysis, catalyst and reactants are present in different phases where as in case of homogeneous catalysis catalyst and reactants are present in same phase.

Question 9.
What are enzymes ? What is their role in human body ?
Answer:
Enzymes are complex nitrogenous organic compounds which are produced by living plants and animals.

• These act as specific catalysts in biological reactions.
• These catalyse the numerous reactions that occur in the bodies of animals and plants to maintain the life process.

Question 10.
Name any two enzyme catalyzed reactions. Give the reactions.
Answer:
1) Inversion of Cane Sugar :

2) Decomposition of urea into ammonia and CO₂ :

Question 11.
What is critical micelle concentration (CMC) and kraft temperature (T_k) ?
Answer:
The formation of micelles takes place only above a particular temperature called Kraft temperature (T_k) and above a particular concentration called Critical micelle concentration (CMC).

Question 12.
What is Peptization ?
Answer:
Peptization : The process of converting a precipitate into colloidal sol by shaking it with the dispersion medium in the presence of a small amount of electrolyte is called Peptization.

Question 13.
What is Brownian movement.
Answer:
Brownian movement: This is a kinetic property of colloidal solution.

When a colloidal solution is examined by ultramicroscope, the colloidal particles are seemed to be moving in a rapid zig-zag motion.
This rapid motion of colloidal particles is called Brownian movement.
This motion is due to unequal bombardment of colloidal particles by molecules of dispersion medium. Smaller the colloidal particles the more rapid is the Brownian movement.

Question 14.
What is Tyndall effect ?
Answer:
Tyndall effect : When light enters a colloidal solution, it is scattered by the large sized colloidal dispersed phase particles. Therefore when light passes through a solution we will be able to see the path of the light as a luminous beam. This is called Tyndall effect.

This is an optical property exhibited by colloidal solution. This phenomenon is clearly seen with a microscope placed at right angles to the path of light. Colloidal particles become self luminous due to absorption of light. A true solution does not show Tyndall effect.

Question 15.
What is electrokinetic potential or zeta potential ?
Answer:
In a colloidal sol the charges of opposite signs on the fixed and diffused parts of the double layer results in a difference in potential between these layers. The potential difference between the fixed layer and the diffused layer of opposite charge is called electro kinetic potential (or) zeta potential.

Question 16.
What is electrophoresis ?
Answer:
When electric potential is applied across two platinum electrodes dipping in a colloidal solution, the colloidal particles move towards one or the other electrode. The movement of colloidal particles under an applied emf is called “electrophoresis”.

Question 17.
What is coagulation ?
Answer:
The stability of the lyophilic sols is due to the presence of charge on the colloidal particles. If this charge is neutralised the particles will come nearer to each other to form aggregates (or coagulate) and settle down under the force of gravity. This process of settling downward colloidal particles is called coagulation (or) flocculation (or) precipitation.

Question 18.
State Hardy – Schulze rule.
Answer:
Greater the valence of the coagulating ion added, the greater is its power to cause coagulation. This is known as Hardy-Schulze rule.

Question 19.
What is protective colloid ?
Answer:
Lyophilic colloids used for the prevention of coagulation of lyophobic colloids are called protective colloids.

• Lyophilic colloids protect the lyophobic colloids. .

Question 20.
What is an emulsion ? Give two examples. (AP Mar. 17)
Answer:
Emulsion : The colloidal system in which a dispersion of finely divided droplets of a liquid in another liquid medium is called emulsion. Eg : Milk, Vanishing cream, Cold cream.

Question 21.
What is an emulsifying agent ?
Answer:
Emulsifying agent: The third substance which is added in small amounts to an emulsion to stabilize the emulsion is called emulsifying agent.

Question 22.
Name any two applications of colloidal solutions.
Answer:
Applications of colloidal solutions :
Rubber: Plant latex is a colloidal solution of rubber particles which are negatively charged. Rubber is obtained from latex by coagulation.
Industrial Products: Paints, inks, synthetic plastics, rubber, graphite, lubricants, cement, etc., are all colloidal in nature.

Question 23.
Define the terms adsorbate and adsorbent.
Answer:
The substance which is adsorbed is called adsorbate. The substance on whose surface the adsorption takes place is called adsorbent.

Question 24.
What is Gold number ?
Answer:
The number of milligrams of a protective colloid required to prevent the coagulation of 10ml Gold sol when 1 ml of 10% NaCl solution is added is called Gold number.

Short Answer Questions

Question 1.
What are different types of adsorption ? Give any four differences between characteristics of these different types. (IPE Mar & May 2015 (AP), (TS), 2016 (TS))
Answer:
Adsorption process is divided into two types.

1. Physisorption
2. Chemisorption.

Distinguishing characteristics of Physisorption and Chemisorption are given in the following table:

Physisorption

1. This process is weak, due to Vander Waals forces.
2. The process is reversible.
3. This is a quick process i.e., takes place quickly.
4. The process decreases with increase of temperature.
5. This is a multilayered process.
6. The process depends mainly on the nature of the adsorbent.

Chemisorption

1. This process is strong, due to chemical forces.
2. The process is irreversible.
3. This is a slow process.
4. The process increases with increase of temperature.
5. This is a unilayered process.
6. The process depends both on the nature of adsorbent and adsorbate.

Question 2.
What is catalysis ? How is catalysis classified? Give two examples for each type of catalysis. (IPE 2015 (AP), 14, BMP. 2016 (AP))
Answer:
Catalysis : A substance which alters the rate of a chemical reaction without itšelf being consumed in the process, is called a catalyst.
The action of catalyst in altering the rate of a chemical reaction is called catalysis
Types of catalysis : Catalysis is classified into two týpes as
a) Homogeneous catalysis and
b) Heterogeneous catalysis.

Homogeneous catalysis: The catalytic process in which the catalyst is present in the same phase as that of reactants, is known as homogeneous catalysis.

Heterogeneous catalysis : The catalytic process in which the catalyst is present in a phase different from that of the reàctants is known as heterogeneous catalysis.

Question 3.
How can the constants k and n of the Freundlich adsorption equation be calculatéd?
Answer:
Freundlich adsorption isotherm equation is
\(\frac{x}{m}\) = k. P^1/n ⇒ x/m = Extent of adsorption ⇒ P = Pressure
k and n are constants which depend on the nature of the adsorbent and the gas at a particular temperature.
Applying logarithm to the above equation
log \(\frac{x}{m}\) = log k + \(\frac{1}{n}\) log P.

• A graph is plotted taking log \(\frac{x}{m}\) on y – axis and log P on x – axis. If the graph is a straight line then Freundlich isotherm is valid.
• The slope of the straight line gives \(\frac{1}{n}\) value.
• The intercept on the y-axis gives value of log k.
• \(\frac{1}{n}\) has values between 0 and 1.
  When \(\frac{1}{n}\) = 0, \(\frac{x}{m}\) = constant, the adsorption is independent of pressure.
  \(\frac{1}{n}\) = 1, \(\frac{x}{m}\) = kP i.e., \(\frac{x}{m}\) ∝ p.

Question 4.
How are colloids classified on thé basis of interaction between dispersed phase and dispersion medium?
Answer:
Lyophilic colloid : The colloidal solution in which the dispersed phase has great affinity to the dispersion medium is called a Lyophilic colloid or Lyophilic solution.
Ex: Starch solution.

The starch paste when dissolved in hot water, with stirring, the starch solution is formed. The starch particles (dispersed phase) has great affinity to water molecules (dispersion medium). So starch solution is a lyophilic solution or lyophilic colloid.

Lyophobic colloid : The colloidal solution in which there exists not much affinity between the dispersed phase and dispersion medium, it is called a Lyophobic colloid or Lyophobic solution.
Ex: Gold solution.

Gold rods are placed in water containing alkali. Electric arc is applied between gold rods. The gold particles dissolves in water, to give gold solution.
Gold particles (dispersed phase) have not much affinity towards water (dispersion medium). So this is a Lyophobic solution or Lyophobic colloid.

Question 5.
Explain any 2 methods for the preparation of colloids.
Answer:
Method – 1: Bredig’s arc Method : This process consists of dispersion and condensation colloids of Gold, Platinum, Silver arc prepared by this method. In this method an electric arc is struck between the electrodes of the metal immersed in the dispersion medium. The heat produced vapourises the metal which then condensed to colloidal size.

Method – 2 : Colloids can be prepared by chemical reactions like double decomposition, oxidation, reduction and hydrolysis.
Double decomposition : As₂O₃ + 3H₂S → AS₂S₃ (sol) + 3H₂O
Oxidation : SO₂ + 2H₂S → 3S(sol) + 2H₂O
Reduction : 2 AuCl₃ + 3 HCHO + 3 H₂O → 2 Au (sol) + 3HCOOH + 6HCl
Hydrolysis : FeCl₃ + 3H₂O → Fe (OH)₃ (sol) + 3HCl

Question 6.
Discuss the use of colloids in
i) Purification of drinking water
ii) Tanning
iii) Medicines.
Answer:
i) Purification of drinking water: The water obtained from natural sources often contains suspended impurities. Alum is added to such water to coagulate the suspended impurities and make water fit for drinking purposes.

ii) Tanning : Animal skins are colloidal in nature. When a skin, which has positively charged particles, is soaked in tannin, which contains negatively charged colloidal particles, mutual coagulation takes place. This results in the hardening of skin (leather). This process is termed as tanning. Chromium salts are also used in place of tannin.

iii) Medicines : Most of the medicines are colloidal in nature. For example argyrol is a silver sol used as an eye lotion. Colloidal antimony is used in curing kalaazar. Colloidal gold is used as intramuscular injection. Milk of magnesia an emulsion, is used for stomach disorders. Colloidal medicines are more effective because they have large surface area and are therefore easily assimilated.

Question 7.
What do you mean by activity and selectivity of catalysts?
Answer:
Activity:
The ability of a catalyst in increasing the rate of reaction is defined as activity of catalyst.

• The activity of a catalyst depends upon the strength of chemisorption to a large extent.
• The reactants must get adsorbed reasonably strongly onto the catalyst to become reactive.
  Eg: The catalystic activity increases from Group – 5 to Group – 11 for hydrogenation reactions.
  The maximum activity being shown by 7 – 9 group metals.
  

Selectivity:
The selectivity of a catalyst is its ability to direct a reacti6n to form specific products. The following reactions indicate the selectivity of heterogeneous catalysis.

• Starting with H₂ and CO, and using different catalysts, we get different products,
  

The action of a catalyst is highly sélective in nature. A substance which acts as a catalyst in one reaction may fail to catalyse another reaction.

Question 8.
What are emulsions? How are they classified? Describe the applications of emulsion. ( AP Mar. 2017; IPE 2016 (TS))
Answer:
Emulsion : The colloidal system in which a dispersion of finely divided droplets of a liquid in another liquid medium is called emulsion.
Ex: Milk.
In Milk, the droplets of liquid fat are dispersed in water. This is an example for oil in water type emulsion.
Classification of emulsions: Emulsions are classified into two classes. These are
a) Oil in Water (O/W) and
b) Water in Oil (W/O), (O = Oil; W = Water).

These emulsions are classified as such depending on which is dispersed phase and which is dispersion medium.

a) Oil in Water (O/W) type emulsions : In this type of emulsions, the dispersed phase is oil and the dispersion medium is water.
Ex: Milk, liquid, fat (oil) in water.
Vanishing cream; fat in water.

b) Water In Oil (W/O) type emulsions : In this type of emulsions, the dispersed phase is water and the dispersion medium is oil.
Ex : Stiff greases : water in lubrication oils
Cod liver oil : water in cod liver oil

Applications of Emulsions : Emulsions are useful

• In the digestion of fats in intestines.
• In washing processes of clothes and crockery.
• In the preparation of lotions, creams, ointments in pharmaceutical and cosmetics.
• In the extraction of metals (froth floatation).
• In the conversion of cream into butter by churning.
• To break oil and water emulsions in oil wells.
• In the preparation of oily type of drugs for easy adsorption to the body.

Question 9.
What is adsorption? Explain different types of adsorptions with suitable examples.
Answer:
The process of concentration of molecules of a gas (or) liquid on the surface of another substance is called adsorption. Adsorption is of two types,
(a) Physical adsorption
(b) Chemical adsorption.

a) Physical adsorption: It is also called Vander waals adsorption. A very weak Vander forces of attraction exists between adsorbate and adsorbent. It is multi layered and non-selective.
Ex: Adsorption of inert gases on activated coconut charcoal.

b) Chemical adsorption: It is also called chemisorption. A very strong chemical forces of attraction exists between adsorbate and adsorbent. It is mono-layered and highly selective.
Ex: Adsorption of H₂ gas on nickel surface.

Students get through AP Inter 2nd Year Chemistry Important Questions Lesson 3(b) Chemical Kinetics which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions Lesson 3(b) Chemical Kinetics

Very Short Answer Questions

Question 1.
What is Rate of a reaction ?
Solution:
Rate of reaction : The rate [speed or velocity] of a reaction is the change in concentration of reactants or products per unit time.
Rate = \(\frac{\Delta x}{\Delta t}\) Where, Δx is the change in concentration, At is the time interval.
The rate of reaction is always positive and it decreases as the reaction proceeds.
For the reaction, R → P, rate may be expressed as

Question 2.
What is Rate equation (or) Rate expression (or) Rate Law ?
Answer:
Rate equation or Rate expression or Rate Law is the mathematical expression in which aA + bB → cC + dD reaction rate is given in terms of molar concentration of reactants. Where a, b, e and d are the stoichiometric coefficients of reactants and products.
The rate expression for this reaction is Rate ∝ [A]^x [B]^y
Exponents x and y may or may not equal to stiochiometric coefficients a and b.
Rate = K [A]^x [B]^y Where K is proportionality constant called rate constant.

Question 3.
Write the differences between Order and Molecularity of a reaction. (IPE 2014, BIE) (A.P. Mar. ’18)
Solution:
Differences between Order and Molecularity of a reaction :

Order of reaction

1. Order is the sum of powers of concentration terms of reactants in the rate law.
   aA + bB → cC + dD Rate = K [A]^x [B]^y
   x + y is the total order of the reaction. x and y may or may not be equal to a and b respectively.
   Ex : 2H₂O₂ → 2H₂O + O₂ is an example for first order reaction.
2. It is determined by experiment.
3. It may be zero, positive, fractional 0, 1, 2, 1.5 etc.,

Molecularity of reaction

i) Molecularity is the no. of reacting species taking part in an elementary reaction.
Ex:
i) NH₄NO₂ → N₂ + 2H₂O
(Unimolecular)
Ex : ii) 2HI → H₂ + I₂ (Bimolecular)
Ex: iii) 2NO + O₂ → 2NO₂ (Trimolecular)

ii) It is determined by reaction mechanism.

iii) It cant be zero, fractional or negative. It is always a whole number.

Question 4.
The rate constant of a first order reaction (K) is 5.5 × 10^-14 sec^-1. Find the half life. (IPE 2015(AP))
Solution:
Half life for a first order reaction is, t_1/2 = \(\frac{0.693}{\mathrm{~K}}\)
t_1/2 = \(\frac{0.693}{5.5 \times 10^{-14} \mathrm{~S}^{-1}}\) = 1.26 × 10¹³S

Question 5.
What is Zero Order reaction ?
Solution:
Zero Order reaction: The rate of reaction is independent of the concentration of reactants.
For the reaction R → P, Rate = –\(\frac{\mathrm{d}[\mathrm{R}]}{\mathrm{dt}}\) = k[R]
[R] – Concentration of reactant
K – First order rate constant
Ex:
1) Decomposition of NH₃ on hot Pt surface ;
2) Decomposition of HI on Gold surface is a zero order reaction

Question 6.
What is First Order reaction ? Give example. (IPE 2014)
Solution:
First Order reaction: The rate of reaction which depends only on one concentration term.
For the reaction R → P, Rate = \(-\frac{d[R]}{d t}\) = k[R]
[R] – Concentration of reactant
K – First order rate constant
Ex:

1. Decomposition of N₂O₅ N₂O₅ (g) → 2NO₂(g) + 1/2 O₂ (g)
2. Decomposition of N₂O N₂O_(g) → N_2(g) + 1/2 O_2(g).

Question 7.
What are pseudo first order reactions ? Give one example.
Answer:
First order reactions whose molecularity is more than one are called pseudo first order reactions.

Order = 1
molecularity = 2

Question 8.
What is Half life of a reaction ?
Solution:
Half life of a reaction: The time in which the concentration of a reactant is reduced to one half of its initial concentration is called half life period. It is represented by t_1/2.
t_1/2 of n^th order reaction is given by t_1/2 ∝ [R₀]^1-n
Where R₀ is initial concentration
t_1/2 = \(\frac{\left[R_{0}\right]}{2 k}\) for a zero order reaction; t_1/2 = \(\frac{0.693}{k}\) for first order reaction

Question 9.
Define the speed or rate of a reaction.
Answer:
The change in the concentration of a réactant (or) product in unit time is called speed or rate of a reaction.
(or)
The decrease in the concentration of a reactant (or) increase in the concentration of product per unit time.

Question 10.
Define Order of a reaction. Illustrate your answer with an example. (IPE 2015; T.S. Mar. ’15)
Answer:
Order of a reaction : The sum of the powers of the concentration terms of the reactants present in the rate equation is called order of a reaction.

• Order of a reaction can be 0, 1, 2, 3 and even a fraction.

Eg:

1. N₂O₅ → N₂O₄ + \(\frac{1}{2}\)O₂
   rate ∝ [N₂O₅]
   ∴ It is a first order reaction.
2. 2N₂ → 2N₂ + O₂
   rate ∝ [N₂O]²
   ∴ It is 2^nd first order reaction.

Question 11.
What are elementary reactions?
Answer:
The reactions taking place in one step are called elementary reactions.

Question 12.
Give two examples for zero Order reactions.
Answer:
Examples for zero order reactions

Question 13.
Write the integrated equation for a first order reaction in terms of [R], [R₀] and ‘t’.
Answer:
[R] = Concentration of reaction after time T
[R₀] = Initial concentrations of reactant
∴ k = \(\frac{2.303}{t}\)log\(\frac{\left[R_0\right]}{[R]}\)
This is the integrated equation for a first order reaction

Question 14.
Give two examples for gaseous first order reactions.
Answer:
The following are the examples for gaseous first order reactions

Question 15.
What is a second order reaction? Give one example.
Solution:
Second order reaction : The reactions in which the rate of reaction depends on changing concentration of two substances is called second order reaction.
Ex : Alkaline hydrolysis of ester.

Question 16.
A reaction has a half – life of 10 minutes. Calculate the rate constant for the first order reaction. (IPE 2016 (TS)
Solution:
In case of first order reaction t_1/2 = \(\frac{0.693}{k}\)
∴ k = \(\frac{0.693}{\mathrm{t}_{1 / 2}}\) = \(\frac{0.693}{10}\) = 0.0693 min^-1

Question 17.
In a first order reaction, the concentration of the reactant is reduced from 0.6 mol/L to 0.2 mol/L in 5 min. Calculate the rate constant (k).
Solution:
a = 0.6mol L^-1; a – x = 0.2 mol L^-1; t = 5 min.
Since it is a first order reaction.
k = \(\frac{2.303}{\mathrm{t}}\) log₁₀ \(\frac{a}{(a-x)}\)
k = \(\frac{2.303}{t}\) log \(\frac{0.6}{0.2}\) = 0.2197 min^-1

Short Answer Questions

Question 1.
Define and explain the order of a reaction. How is it obtained experimentally ?
Answer:
Order of a reaction : The sum of the powers of the concentration terms of the reactants present in the rate equation is called order of a reaction.

• Order of a reaction can be 0, 1, 2, 3, and even a fraction.

Eg:

1) N₂O₅ → N₂O₄ + \(\frac{1}{2}\)O₂
rate ∝ [N₂O₅]
∴ It is a first Order reaction.

2) 2N₂ → 2N₂ + O₂
rate ∝ [N₂O]²
∴ It is 2^nd order reaction

• Order of a reaction can be determined experimentally.

Half-Time (t_1/2) method: The time required for the initial concentration (a) of the reactant to become half its value (a/2) during the progress of the reaction is called half-time (t_1/2) of the reaction.
A general expression for the half life, (t_1/2) is given by
t_1/2 ∝ \(\frac{1}{a^{n-1}}\)

Therefore, for a given reaction two halftime values (t’_1/2 and t”_1/2) with initial concentrations a’ and a” respectively are determined experimentally and the order is established from the equation.
\(\left(\frac{\mathrm{t}_{1 / 2}^{\prime}}{\mathrm{t}_{1 / 2}^{\prime}}\right)\) = \(\left(\frac{a^n}{a^{\prime}}\right)^{n-1}\)
Where ‘n’ is the order of the reaction.

Question 2.
Describe the salient features of the collision theory of reaction rates of bimolecular reactions.
Answer:
Collision theory of reaction rate bimolecular reactions salient features.

• The reaction molecules are assumed to be hard spheres.
• The reaction is postulated to occur when molecules collide with each other.
• The number of collisions per second per unit volume of the reaction mixture is known as collision frequency (Z).
• For a bimolecular elementary reaction.

A + B → products
Rate = Z_AB. e^-E_a/RT ; Z_AB = collision frequency.

• All collisions do not lead to product formation.
• The collisions with sufficient kinetic energy (Threshold energy) are responsible for product formation. These are called as effective collisions.
• To account for effective collisions a factor p called to probability factor or steric factor is introduced.
  Rate = P Z_AB. e^-E_a/RT

Question 3.
What is “moleculartiy” of a reaction ? How is it different from the ‘order’ of a reaction ? Name one bimolecular and one trimolecular gaseous reactions.
Answer:
The number of reacting species (atoms, ions or molecules) taking parts in an elementary reaction, which must colloid simultaneously to bring about a chemical reaction is called molecularity of a reaction.
NH₄NO₂ → N₂ + 2H₂O (Unimolecular)
2HI → H₂ + I₂ (Bimolecular)
2NO + O₂ → 2NO₂ (Trimolecular)

• Molecularity has only integer values (1, 2, 3, ….)
• It has non zero, non fraction values while order has zero, 1, 2, 3, ….. and fractional values.
• It is determined by reaction mechanism, order is determined experimentally.

Question 4.
What is half-life (t_1/2) of a reaction ? Derive the equations for the ‘half-life’ value of zero and first order reactions.
Answer:
The time required for the initial concentration of the reactants to become half of it’s value during the progress of the reaction is called half life (t_1/2) of reaction.
Eg : The radio active of C-14 is exponential with a half life of 5730 years.
Half life of zero order reaction :

Question 5.
Explain the terms
a) Activation energy (E_a)
b) Collision frequency (Z)
c) Probability factor (P) with respect to Arrhenius equation.
Answer:
a) Activation Energy: The energy required to form an intermediate called activated complex (C) during a chemical reaction is called activation energy.

b) Collision frequency: The number of collisions per second per unit volume of the reaction mixture is called collision frequency (Z). For a bimolecular elementary reactions
A + B → products

c) Probability factor (P) with respect to Arrhenius equation : To account for effective collisions a factor p called to probability factor or steric factor is introduced.

Question 6.
Explain the factors influencing rate of reaction. (IPE 2015 (TS))
Solution:
Factors affecting rate of a reaction: The rate of a chemical reaction depends on the following.

i) Concentration of reactants : The rate of a chemical reaction is directly proportional to the concentration of the reactants. As the concentration of reactants increases the number of molecules increase, collisions between molecules increases as a result number of fruitful collisions increases, hence rate of reaction increases.

ii) Nature of reactants : Reactions between ionic compounds are fast when compared to reactions between the covalent compounds. In case of ionic reactions only exchange of ions takes place, hence the reactions between ionic compounds in solutions are very fast. In case of covalent molecules breaking and formation of bonds involved hence the reactions between covalent molecules are very slow.

iii) Temperature : As temperature increases, the rate of reaction increases. For every 10°C rise of temperature the rate of reaction is almost doubled. At high temperatures maximum number of molecules are activated. The collisions between activated molecules are fruitful, hence the rate of reaction increases.

iv) Catalyst: In the presence of catalyst also the rate of reaction increases. Catalyst takes the reaction in a new path having low activation energy.

Question 7.
Show that in the case of first order reaction, the time required for 99.9% completion of the reaction is 10 times that required for 50% completion. (log 2 = 0.3010)
Solution:
Initial concentration, a = 100; Half life period, t_1/2 = 0.693/K
Concentration after time ‘t’ = a – x = 100 – 99.9 = 0.1
For first order reaction, K = \(\frac{2.303}{t}\)log\(\frac{a}{(a-x)}\)

Question 8.
Derive an integrated rate equation for a first order reaction.
Answer:
In first order reactions rate depends on only one concentration term.
R → P
Rate = k[R]; \(\frac{\mathrm{d}[\mathrm{R}]}{\mathrm{dt}}\) = -k. dt
Integration on both sides
ln[R] = -kt + I ——- (1)
I = Integration constant
At t = 0, [R] = [R₀] ⇒ l_n[R₀] = I
Substituting I = ln [R] in the above equation (1)
lñ [R] = -kt + ln[R₀]
ln \(\frac{[\mathrm{R}]}{\left[\mathrm{R}_0\right]}\) =-kt . ——— (2)
k = \(\frac{1}{\mathrm{t}} \ln \frac{\left[\mathrm{R}_0\right]}{[\mathrm{R}]}\)
Taking antilog on both sides of eq. (2)
R = [R_o]. e^-kt
This is first order rate equation.

Students get through AP Inter 2nd Year Chemistry Important Questions Lesson 3(a) Electro Chemistry which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions Lesson 3(a) Electro Chemistry

Very Short Answer Questions

Question 1.
What is a galvanic cell or a voltaic cell ? Give one example.
Answer:
Galvanic cell: A device which converts chemical energy into electrical energy by the use of spontaneous redox reaction is called Galvanic cell (or) voltaic cell.
Eg.: Daniell cell.

Question 2.
What is standard hydrogen electrode ?
Answer:
The electrode whose potential is known as standard electrode (or) standard hydrogen electrode.
To determine the potential of a single electrode experimentally it combine with standard hydrogen electrode and the EMF of cell so constructed is measured with potentiometer.

Question 3.
What is Nernst equation ? Write the equation for an electrode with electrode reaction
Mⁿ⁺ (aq) + ne^– \(\rightleftharpoons\) M_(s).
Answer:
The electrode potential at any concentration measured with respect to standard hydrogen electrode is represented by Nernst equation.
Nernst equation is

Here, E_(Mⁿ⁺/M) = Electrode potential
E⁰_(Mⁿ⁺/M) = Standard electrode potential
R = gas constant = 8.3 14 J/k.mole
F = Faraday = 96487 c/mole
T = temperature .
[Mⁿ⁺] = concentration of species Mⁿ⁺

Question 4.
How is E⁰ cell related mathematically to the equilibrium constant K_c of the cell reaction?
Answer:
Relation between E₀ cell and equilibrium constant K_c of the cell reaction
\(E_{\text {cell }}^0\) = \(\frac{2.303 \mathrm{RT}}{\mathrm{nF}} \log \mathrm{K}_{\mathrm{c}}\)
n = number of electrons involved
F = Faraday = 96500 C mol^-1
T = Temperature
R = gas constant

Question 5.
How is Gibbs energy (G) related to the cell emf (E) mathematically ?
Answer:
Relation between Gibb’s energy (G) and emf (E) mathematically
ΔG° = – nFE_(cell)
ΔG = change in Gibb’s energy
n = number of electrons involved
F = Faraday = 96500 C mol^-1

Question 6.
Define conductivity of a material. Give its SI units.
Answer:
The reciprocal of specific resistance (or) resistivity is called conductivity. It is represented by (K)
(Or)
The conductance of one unit cube of a conductor is also called conductivity.
SI units : ohm^-1 m^-1 (or) Sm^-1 S = Siemen

Question 7.
What is cell constant of a conductivity cell ?
Answer:
Cell constant:

The cell constant of a conductivity cell is the product of resistance and specific conductance.

Question 8.
State Faraday’s second law of electrolysis.
Answer:
The amounts of different substances liberated when the same quantity of electricity is passed through the electrolytic solution are proportional to their chemical equivalent weights.
m ∝ E

Question 9.
State Kohlrausch’s law of independent migration of ions.
Answer:
Kohlrausch’s law of independent migration of ions : The limiting molar conductivity of the electrolytes can be represented as the sum of the individual contributions of the anion and the cation of the electrolytes.
\(\lambda_{m(A B)}^0\) = \(\lambda_{\mathrm{A}^{+}}^0\) + \(\lambda_{\mathrm{B}^{-}}^0\)
\(\lambda_m^0\) = Limiting molar conductivity
\(\lambda_{\mathrm{A}^{+}}^0\) = Limiting molar conductivity of cation ‘
\(\lambda_{\mathrm{B}^{-}}^0\) = Limiting molar conductivity of anion

Question 10.
State Faraday’s first law of electrolysis.
Answer:
The amount of chemical reaction which occurs at any electrode during electrolysis is proportional to the quantity of current passing through the electrolyte.
(Or)
The mass of the substance deposited at an electrode during the electrolysis of electrolyte is directly proportional to quantity of electricity passed through it.
m ∝ Q; m ∝ c × t
m = ect; m = \(\frac{\text { Ect }}{96,500}\)
e = electrochemical equivalent
t = time in seconds
c = Current in amperes
E = Chemical equivalent

Question 11.
What is a primary battery? Give one example. (AP Mar. ’17)
Answer:
The batteries which after their use over a period of time, becomes dead and the cell reaction is completed and this cannot be reused again are called primary batteries.
Eg: Leclanche cell, dry cell.

Question 12.
Give one example for a secondary battery. Give the cell reaction.
Answer:
Lead storage battery is an example of secondary battery.
The cell reactions when the battery is in use are

Question 13.
What is metallic corrosion? Give one example. (TS Mar. 2017, IPE ‘15 (AP))
Answer:
Metallic corrosion : The natural tendency of conversion of a metal into its mineral compound form on interaction with the environment is known as metallic corrosion.
Eg:

1. Iron converts itself into its oxide.
   [Rusting] (Fe₂O₃)
2. Silver converts itself into it’s sulphate
   [tarnishing] [Ag₂S]

Question 14.
Define electrochemical equivalènt (e.c.e).
Answer:
The weight of the substance deposited or liberated when one ampere of current is passed for 1 second (1 coloumb) is called electrochemical equivalent (e.c.e).

Question 15.
A solution of CuSO₄ is electrolysed for 10 minutes with a current of 1.5 amperes. What is the mass of copper deposited at the cathode? (IPE 2015 (AP), 14)
Solution:
t =600 s charge = current × time = 1.5A × 600 s = 900 C
According to the reaction:

We require 2F or 2 × 96487 C to deposit 1 mol or 63 g of Cu.

Question 16.
Can you store copper sulphate solutions in a zinc pot ?
Solution:
No, zinc pot cannot store copper sulphate solutions because the standard electrode potential (E⁰) value of zinc is less than that of copper. So, zinc is stronger reducing agent than copper.

So, zinc will loss electrons to Cu²⁺ ions and redox reaction will occur as follows.

Question 17.
Write the cell reaction taking place in the cell, Cu(s) / Cu²⁺ (aq) //Ag⁺ (aq) / Ag (s).
Answer:
Cu_(s)/Cu⁺²_(aq)//Ag⁺_(aq)/Ag
In the above notation copper electrode acts as anode and silver electrode acts as cathode.

Question 18.
Write the Nernst equation for the EMF of the cell

Answer:

Question 19.
Write the cell reaction for which

Answer:

Short Answer Questions

Question 1.
What are galvanic cells ? Explain the working of a galvanic cell with a neat sketch taking Daniell cell as example.
Answer:
Galvanic cell: A device which converts chemical energy into electrical energy by the use of spontaneous redox reaction is called Galvanic cell (or) voltaic cell. Eg : Daniell cell.

Daniell cell: It is a special type of galvanic cell. It contains two half cells in the same vessel. The vessel is divided into two chambers. Left chamber is filled with ZnSO₄ (aq) solution and Zn – rod is dipped into it. Right chamber is filled with aq. CuSO₄ solution and a copper rod is dipped into it. Process diaphragm acts as Salt bridge. The two half cell’s are connected to external battery.

Cell reactions :
Ion Zn/ZnSO₄ half cell, oxidation reaction occurs.
Zn → Zn²⁺ + 2e^–
Ion Cu/CuSO₄ half cell, reduction reaction occurs.
Cu⁺² + 2e^– → Cu
The net cell reaction is
Zn + Cu⁺² \(\rightleftharpoons\) Zn⁺² + Cu
Cell is represented as Zn / Zn⁺² || Cu²⁺ / Cu

Question 2.
Give the construction and working of a standard hydrogen electrode with a neat diagram.
Answer:
To determine the potential of a single electrode experimentally, it is combined with a standard hydrogen electrode (electrode whose potential is known) and the EMF of the cell so constructed is measured with a potentiometer. Standard Hydrogen Electrode is constructed and is used as standard electrode or reference electrode. Standard Hydrogen Electrode (SHE) or Normal Hydrogen Electrode (NHE).

Pure hydrogen gas is bubbled into a solution of 1M HCl along a platinum electrode coated with platinum block. A platinum block electrode placed in the solution at atmospheric pressure.

Generally the electrode is fitted into the tube. The tube will have two circular small holes. This tube is immersed in the acid solution such that one half of the circular hole is exposed to air and another half in the solution.

The following equilibrium exists at the electrode.
\(\frac{1}{2} \mathrm{H}_{2(\mathrm{~g})}\left(1_{\mathrm{atm}}\right) \rightleftharpoons \mathrm{H}_{(\mathrm{aq})}^{+}(\mathrm{M})+\mathrm{e}^{-}\)

Question 3.
State and explain Kohlrausch’s law of independent migration of ions. (IPF. 2015, BMP, 2016 (TS)
Answer:
Kohlrausch’s law of independent migration of ions : The limiting molar conductivity of the electrolytes can be represented as the sum of the individual contributions of the anion and the cation of the electrolytes.
\(\lambda_{\mathrm{m}(\mathrm{AB})}^0=\lambda_{\mathrm{A}^{+}}^0+\lambda_{\mathrm{B}^{-}}^0\)
\(\lambda_{\mathrm{m}}^0\) = Limiting molar conductivity
\(\lambda_{\mathrm{A}^{+}}^0\) = Limiting molar conductivity of cation
\(\lambda_{\mathrm{B}^{-}}^0\) = Limiting molar conductivity of anion,

Applications :

1. Kohlrausch’s law is used in the calculation of the limiting molar conductivity of weak electrolytes.
   
2. This law is used in the calculation of degree of dissociation of a weak electrolyté.
3. This law is used in the calculation of solubility of sparingly soluble salts like AgCl, BaSO₄ etc.

Question 4.
What is electrolysis? Give Faraday’s first law of electrolysis. (IPE 2014)
Answer:
Electrolysis : The decomposition of a chemical compound in the molten state or in the solution state into its constituent elements under the influence of an applied EMF is called electrolysis.
The amount of chemical reaction which occurs at any electrode during electrolysis is proportional to the quantity of current passing through the electrolyte.
(Or)
The mass of the substance deposited at an electrode during the electrolysis of electrolyte is directly proportional to quantity of electricity passed through it.

e = electrochemical equivalent
t = time in seconds
c = Current in amperes
E = Chemical equivalent

Question 5.
Calculate the emf of the cell at 25°C Cr | Cr³⁺ (0.1 M) || Fe²⁺ (0.01M)| Fe, given that

Answer:
Given cell is

Question 6.
Determine the values of K_c for the following reaction.

Solution:

Question 7.
If a current of 0.5 ampere flows through a metallic wire for 2h, then how many electrons would flow through the wire ?
Solution:
Quantity of charge (Q) passed = Current (C) × Time (t)
= (0.5 A) × (2 × 60 × 60 s)
= (3600) Ampere sec = 3600 C
Number of electrons flowing through the wire on passing charge of one Faraday (96500 C) = 6.022 × 10²³
Number of electrons flowing through the wire on passing a charge of 3600 C
= \(\frac{6.022 \times 10^{23} \times(3600 \mathrm{C})}{(96500 \mathrm{C})}\)
= 2.246 × 10²²
Number of electrons = 2.246 × 10²²

Question 8.
Define emf. Calculate the emf of the following galvanic cell:

Solution:
EMF : The difference in electrode potentials between reduction potential of cathode and reduction potential of anode is called emf.
emf = reduction potential of cathode – reduction potential of anode
emf = + 0.34 – (-0.76) ⇒ + 0.34 + 0.76 = 1.1V

Question 9.
Write Nernst equation for a metal and non metal eletrode.
Solution:
For a metal electrode M : M_+n (aq) + ne^– → M(s)

Students get through AP Inter 2nd Year Chemistry Important Questions 2nd Lesson Solutions which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions 2nd Lesson Solutions

Very Short Answer Questions

Question 1.
Define molarity. [AP IPE ’15] [TS Mar. ’17 ’11]
Answer:
Molarity: The number of moles of solute dissolved in one litre of solution is called molarity.

Units : moles / kg.

Question 2.
Define molality. [AP IPE 2015, May ’11]
Answer:
Molality : The number of moles of solute present in one kilogram of solvent is called molality.

Units : moles / kg.

Question 3.
Define mole fraction. (AP IPE 2015, Mar. ’14)
Answer:
Mole fraction : The ratio of number of moles of the one component of the solution to the total number of moles of all the components of the solution is called mole fraction.
Mole fraction of solute X_s = \(\frac{n_{\mathrm{s}}}{\mathbf{n}_0+\mathrm{n}_{\mathrm{s}}}\)
Mole fraction of solvent X₀ = \(\frac{\mathrm{n}_{\mathrm{s}}}{\mathrm{n}_0+\mathrm{n}_{\mathrm{s}}}\)
[n_s = number of moles of solute
n₀ = number of moles of solvent]
→ It has no units.

Question 4.
State Raoult’s law. (AP Mar. ’17, ’14 IPE ‘16, 14 (AP, TS)
Answer:
Raoult’s law for volatile solute: For a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution.
Raoults law for non-válatlle solute : The relative lowering of vapour pressure of dilute solution containing non-volatile solute is equal to the mole fraction of solute.

Question 5.
State Henrýs law. (TS IPE ’16)
Answer:
At constant temperature, the solubility of a gas in a liquid -is directly proportional to the partial pressure of the gas present above the surface of liquid.
The partial pressure of the gas in vapour phase is proportional to the mole fraction of the gas in the solution.
P = K_H × X
K_H = Henry’s constant
P = Partial pressure
X = Mole fraction of gas

Question 6.
What is Ebullioscopic constant ?
Answer:
Ebullioscopic constant : The elevation of boiling point observed in one molal solution containing non-volatile solute is called Ebullioscopic constant (or) molal elevation constant.

Question 7.
What are isotonic solutions ?
Ans. Isotonic solutions : Solutions having same osmotic pressure at a given temperature are called isotonic solutions.
e.g.: Blood is isotonic with 0.9% (\(\frac{\mathrm{W}}{\mathrm{V}}\)) NaCl [Saline]

Question 8.
What is Cryoscopic constant?
Answer:
Cryoscopic constant : The depression in freezing point observed in one molal solution containing non-volatile solute is called cryoscopic constant (or) molal depression constant.

Question 9.
Define osmosis and osmotic pressure. (IPE 15, (AP) ‘16 (TS), (AP))
Answer:
Osmosis : The spontaneous flow of solvent particles from a solution of lower concentration in to higher concentration through semi permeable membrane is called osmosis.

Osmotic pressure : The pressure required to prevent the flow of solvent particles from pure
solvent into solution through semipermeable membrane is called osmotic pressure.
π = (nRT) / V Here π = Osmotic pressure; V = Volume of solution;
n = No. of moles of solute; R = Universal gas constant: T = Absolute temperature

Question 10.
What is Van’t Hoff’s factor ‘i’ and how is it related to ‘α’ in the case of a binary electrolyte (1:1)?
Answer:
Van’t Hoff’s factor (i): ‘It is defined as the ratio of the observed value of colligative property to the theóretical value of colligative property”.

Solute dissociation or ionization process: If a solute on ionization gives ‘n ions and ‘α’ is degree of ionization at the given concentration, we will have [1 + (n – 1) α] particles.
(1 – α) \(\rightleftharpoons\) nα
Total 1 – α + nα = [1 + (n – 1)α]
∴ i = \(\frac{[1+(n-1) \alpha]}{1}\)
α = \(\frac{\mathrm{i}-1}{\mathrm{n}-1}\)
α_ionization = \(\frac{\mathrm{i}-1}{\mathrm{n}-1}\)
Solute association process:
If ‘n’A molecules combine to give A, we have
nA \(\rightleftharpoons\) A_n
If ‘α’ is degree of association at the given concentration.

Question 11.
What is relative lowering of vapour pressure? [IPE ’16, (TS)]
Answer:
Relating lowering of vapour pressure : The ratio of lowering of vapour pressure of a solution containing non-volatile solute to the vapour pressure of pure solvent is called relative lowering of vapour pressure.
R.L.V.P. = \(\frac{\mathrm{P}_0-\mathrm{P}_{\mathrm{S}}}{\mathrm{P}_0}\)
P₀ – P_S = lowering of vapour pressure
P_o = Vapour pressure of pure solvent

Question 12.
What is vapour pressure of a liquid?
Answer:
The pressure exerted by vapour over liquid when it is in equilibrium with the liquid is called vapour pressure.

Question 13.
What is elevation of boiling point? (IPE 16, (TS) )
Answer:
The boiling point of a solution containing non-volatile solute is higher than the boiling point of pure solvent. The difference in boiling points between solution and pure solvent is called elevation of boiling point.

Question 14.
What is depression of freezing point?
Answer:
The freezing point of a solution containing non-volatile solute is always lower than the freëzing point of puré solvent. The difference in freezing points between solution and pure solvent is called depression of freezing point.

Question 15.
Calculate the amount of benzoic acid (C₆H₅COOH) required for preparing 250 ml of
0.15 M solution in methanol.
Answer:
Given
Molarity = 0.15 M
Volume V = 250 ml
Molecular weight of benzoic acid (C₆H₅COOH) = 122
Molarity (M) = \(\frac{\text { Weight }}{\mathrm{GMw}} \times \frac{1000}{\mathrm{~V}(\mathrm{~m} l)}\)
0.15 = \(\frac{\mathrm{W}}{122} \times \frac{1000}{250}\)
W = \(\frac{122 \times 0.15}{4}\) = 4.575 gms.

Question 16.
Calculate the mole fraction of H₂SO₄ in a solution containing 98% H₂SO₄ by mass. (T.S. Mar. ’18; A.P Mar. ‘17, IPE ‘15, (AP))
Answer:
Given a solution containing – 98% H₂SO₄ by mass.
It means 98 gms of H₂SO₄ and 2 gms of H₂O mixed to form a solution.

Question 17.
Calculate the molarity of a solution containing 5g of NaOH in 450 ml solution. (T.S. Mar. ’19, ’17 )
Solution:
Moles of NaOH = \(\frac{5 \mathrm{~g}}{40 \mathrm{~g} \mathrm{~mol}^{-1}}\) = 0.125 mol
Volume of the solution in litres = 450 mL / 1000 mL L^-1
Using equation

Question 18.
200 cm³ of an aqueous solution of a protein contains 1.26 g of the protein. The osmotic pressure of such a solution at 300 K is found to be 2.57 × 10^-3 bar. Calculate the molar masš of the protein.
Sólution:
The various quantities known to us are as follows : π = 2.57 × 10^-3 bar.
V = 200 cm³ = 0.200 litre
T = 300 K
R = 0.083 L bar moL^-1 K^-1
Substituting these values in equation,
we get M₂ = \(\frac{\mathrm{w}_2 \mathrm{RT}}{\pi \mathrm{V}}\)
M₂ = \(\frac{1.26 \mathrm{~g} \times 0.083 \mathrm{~L} \mathrm{bar} \mathrm{K}^{-1} \mathrm{~mol}^{-1} \times 300 \mathrm{~K}}{2.57 \times 10^{-3} \mathrm{bar} \times 0.200 \mathrm{~L}}\)
= 61.022 g mol^-1

Question 19.
Calculate the molality of 10g of glucose in 90g of water.
Answer:

Question 20.
Calculate the mass percentage of benzene (C₆H₆) and carbon tetrachloride (Ccl₄) if 22g of benzene is dissolved in 122g of carbon tetrachloride.
• Then, calculate the mass percentage from the formula

Solution:
Mass of benzene = 22g; Mass of CCl₄ = 122g
Mass of solution = 22 + 122 = 144g
Mass % of benzene = \(\frac{22}{144}\) × 100 = 15.28%
Mass of CCl₄ = 100 – 15.28 = 84.72%
Note: Mass percent of CCl₄ can also be calculated by using the formula as:
Mass % of CCl₄ = \(\frac{122}{144}\) × 100 = 84.72%

Question 21.
What are colligative properties? Give their names.
Answer:
The properties of a solution which depend on number of solute particles but not on the nature are called colligative properties.
Names:

1. Lowering of vapour pressure
2. Elevation of boiling point.
3. Depression of freezing point.
4. Osmotic pressure.

Question 22.
Calculate the weight of Glucose required to prepare 500 ml of 0.1 M solution. (IPE ‘16, (TS))
Answer:
Molarity = 0.1; Molecular weight of glucose = 180; Volume of solution = 500 ml

Short Answer Questions

Question 1.
What is an ideal solution?
Answer:
A solution of two or more components which obeys Raoult’s law at all concentrations and at all temperatures is called ideal solution. In ideal solution there should not be any association between solute and solvent, (Le.) no chemical interaction between solute and solvent of solution.

Ex : The following mixtures form ideal solutions.

• Benzene + Toluéne ‘
• n – hexane + n – heptane
• ethyl bromide + ethyl iodide

Question 2.
What is relative lowering of vapour pressure? How is it useful to determine the molar mass of a solute?
Answer:
Raoult’s law for volatile solute: For a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution.
Raoult’s law for non-volatile solute : The relative lowering of vapour pressure of dilute solution containing non-volatile solute is equal to the mole fraction of solute.

Relative lowering of vapour pressure \(\frac{\mathrm{P}_0-\mathrm{P}_{\mathrm{s}}}{\mathrm{P}_0}\) = X_s (mole fraction of solute)
\(\frac{\mathrm{P}_0-\mathrm{P}_{\mathrm{s}}}{\mathrm{P}_0}\) = \(\frac{\mathbf{n}_{\mathrm{s}}}{\mathrm{n}_0+\mathrm{n}_{\mathrm{s}}}\)
For very much dilute solutions n_s < < < ….. n₀
∴ \(\frac{\mathrm{P}_0-\mathrm{P}_{\mathrm{s}}}{\mathrm{P}_0}\) = \(\frac{\mathrm{n}_{\mathrm{s}}}{\mathrm{n}_0}\) = \(\frac{\mathrm{w}}{\mathrm{m}}\) × \(\frac{\mathrm{M}}{\mathrm{W}}\)
W = Weight of solute
m = Molar mass of solute
w = Weight of solvent
M = Molar mass of solvent
Molar mass of solute m = \(\frac{w \times M}{W} \times \frac{P_0}{P_0-P_5}\)

Question 3.
The vapour pressure of a solution containing non volatile solute Is less than the vapour pressure of pure of solvent. Give reason.
Answer:
In pure solvent the surface is occupied by solvent molecules only. Number of molecules evapoarating will be more, hence vapour pressure is more. In case of solution the surface is occupied by both solute and solvent molecules. The number of molecules evaporating will be less in case of solution containing non volatile solute. Hence the vapour pressure of solution containing non volatile solute is less than the vapour pressure of pure solvent.

Question 4.
An antifreeze solution is prepared from 222.6g of ethylene glycol [(C₂H₆O₂)] and 200g of water (solvent). Calculate the molality of the solution.
Solution:
Weight of Ethylene glycol = 222.6 gms
G.mol wt = 62

Question 5.
Vapour pressure of water at 293K is 17.535 mm Hg. Calculate the vapour pressure of the solution at 293K when 25g of glucose is dissolved in 450g of water? (BMP)
Answer:
Raoult’s law formula

Question 6.
The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, non-electrolyte solid weighing 0.5g when added to 39.0 g of benzene (molar mass 78 g mol^-1). Vapour pressure-of the solution, then, is 0.845 bar. What is the molar mass of the solid substance? (IPE 2016 (AP))
Solution:
The various quantities known to us are as follows.
\(\mathrm{p}_1^0\) = 0.850 bar
P = 0.845bar
M₁ = 78 g mol^-1
w₂ = 0.5 g
w₁ = 39 g
Substituting these values in equation \(\frac{\mathrm{P}^0-\mathrm{P}}{\mathrm{P}_1^0}\) = \(\frac{\mathrm{w}_2 \times \mathrm{M}_1}{\mathrm{M}_2 \times \mathrm{w}_1}\) we get

Therefore, M₂ = 170 g mol^-1

Question 7.
Vapour pressure of pure water at 298 K is 23.8 mm Hg. 50g urea (NH₂CONH₂) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.
• Consider Raoults law and formula for relative lowering in vapour pressure,
\(\frac{\mathbf{p}_{\mathbf{A}}^0-\mathbf{p}_{\mathrm{s}}}{\mathbf{p}_{\mathbf{A}}^0}\) = \(\frac{\mathbf{n}_{\mathbf{B}}}{\mathbf{n}_{\mathbf{A}}}\) = \(\frac{\mathbf{W}_{\mathrm{B}}}{\mathbf{M}_{\mathrm{B}}}\) × \frac{\mathbf{M}_{\mathbf{A}}}{\mathbf{W}_{\mathbf{A}}}\(\)
Where, \(\frac{\mathbf{p}_{\mathrm{A}}^0-\mathbf{p}_{\mathrm{s}}}{\mathbf{p}_{\mathrm{A}}^0}\) is called relative lowering in vapour pressure.
Solution:

Step 1: Calculation of vapour pressure of water for this solution.
According to Raoult’s law,

(Pure water) \(\mathrm{p}_{\mathrm{A}}^0\) = 23.8 mm; .
W_B (urea) = 50 g; W_A (water) = 850 g
M_B (urea) = 60 g mol^-1; M_A (water) = 180 g mol^-1
Placing the values in eq. (i)

Step II: Calculation of relative lowering of vapour pressure
Relative lowering in vapour pressure = \(\frac{\mathrm{p}_{\mathrm{A}}^0-\mathrm{p}_{\mathrm{s}}}{\mathrm{p}_{\mathrm{A}}^0}\) = \(\frac{(23.8-23.38) \mathrm{mm}}{(23.8 \mathrm{~mm})}\) = 0.0176

Question 8.
A solution of sucrose in water is labelled as 20% w/W. What would be the mole fraction of each component in the solution? (IPE ‘2014)
Answer:
20% \(\frac{w}{W}\) Sucrose in water solution means
20 gms of Sucrose and 80 gms of water.
Number of moles of sucrose (n_s) = \(\frac{20}{342}\) = 0.0584
Number of moles of water (n₀) = \(\frac{80}{18}\) = 4.444
Mole fraction of sucrose X_s = \(\frac{n_s}{n_0+n_s}\)
= \(\frac{0.0584}{4.444+0.0584}\) = \(\frac{0.0584}{4.50284}\) = 0.01296
Mole fraction of water X_o = \(\frac{\mathbf{n}_0}{\mathrm{n}_0+\mathrm{n}_{\mathrm{s}}}\) = \(\frac{4.444}{4.50284}\) = 0.9869
X_s + X₀ = 1
X₀ = 1 – X_s = 1 – 0.01296 = 0.987

Question 9.
Calculate the vapour pressure of a solution containing 9g of glucose in 162g of water at 293K. The vapour pressure of water of 293K is 17.535mm Hg. (IPE ‘15, ’14, BOARD MODEL PAPER)
Solution:
Weight of solute (w) = 9g; Weight of solvent (W) = 162g
Molecular weight of solute (mw) = 180; molecular weight of solvent Mw = 18
Vapour pressure of pure solvent = 17.535 vapour pressure of solution P_s = ?
\(\frac{P_0-P_3}{P_0}\) = \(\frac{W}{m w} \times \frac{M W}{W}\)
⇒ \(\frac{17.535-P_s}{17.535}\) = \(\frac{9}{180} \times \frac{18}{162}\)
17.535 – P_s = 17.535 × \(\frac{9}{180}\) × \(\frac{18}{162}\)
⇒ 17.535 – P_s = 0.0972
∴ P_s = 17.535 – 0.0972 = 17.4378 mm

Students get through AP Inter 2nd Year Chemistry Important Questions 1st Lesson Solid State which are most likely to be asked in the exam.

AP Inter 2nd Year Chemistry Important Questions 1st Lesson Solid State

Very Short Answer Questions

Question 1.
What is meant by the term coordination number ?
Answer:
The number of nearest neighbouring particles of a particle is defined as the co-ordination number.
(Or)
The number of nearest oppositely charged ions surrounding a particular ion is also called as co-ordination number.
E.g.: Co-ordination no. of Na⁺ in NaCl lattice is ‘6’.

Question 2.
What is the co-ordination number of atoms in a cubic close – pack structure ?
Answer:
The co-ordination number of atoms in a cubic close pack structure is ’12’.

Question 3.
What is the co-ordination number of atoms in a body – centered cubic structure ?
Answer:
The co-ordination number of atoms in a body – centered cubic structure is ‘8’.

Question 4.
How do you distinguish between crystal lattice and unit cell ? [Board Model Paper]
Answer:
Crystal lattice : A regular arrangement of the constituent particles of a crystal in the three dimensional space is called crystal lattice.
Unit cell: The simple unit of crystal lattice which when repeated again and again gives the entire crystal of a given substance is called unit cell.

Question 5.
What is Schottky defect ? [A.P. IPE 2015]
Answer:
Schottky defect:

1. “It is a point defect in which an atom or ion is missing from its normal site in the lattice”.
2. In order to maintain electrical neutrality, the number of missing cations and anions are equal.
3. This sort of defect occurs mainly in highly ionic compounds, where cationic and anionic sizes are similar.
   In such compounds the co-ordination number is high.
   Ex.: NaCl, CsCl etc.
4. Illustration :
   
5. This defect decreases the density of the substance.

Question 6.
What is Frenkel defect ? [A.P. IPE 2015]
Answer:
Frenkel defect:

1. “It is a point defect in which an atom or ion is shifted from its normal lattice position”. The ion or the atom now occupies an interstitial position in the lattice.
2. This type of a defect is favoured by a large difference in sizes between the cation and anion. In these compounds co-ordination number is low.
   E.g.: Ag – halides, ZnS etc.
3. Illustration :
   
4. Frenkel defect do not change the density of the solids significantly.

Question 7.
What are f – centers ?
Answer:

• f – centers are the anionic sites occupied by unpaired electrons.
• These import colour to crystals. This colour is due to the excitation of electrons when they absorb energy from the visible light.
• f – centres are formed by heating alkyl halide with excess of alkali metal.
  E.g. : NaCl crystals heated in presence of Na – vapour, yellow colour is produced due to f – centres.

Question 8.
Why X – rays are needed to probe the crystal structure ?
Answer:
According to the principles of optics, the wavelength of light used to observe an object must be no greater than the twice the length of the object itself. It is impossible to see atom s using even the finest optical microscope. To see the atoms we must use light with a wavelength of approximately 10^-10 m. X – rays are present with in this region of electromagnetic spectrum. So X – rays are used to probe crystal structure.

Question 9.
Explain Ferromagnetism with suitable example.
Answer:
Ferromagnetic Substances : Some substances containing more number of unpaired electrons are very strongly attracted by the external magnetic field. In Ferromagnetic substances the magnetic moments in individual atoms are all alligned in the same direction. Such substances are called Ferromagnetic Substances. In ferromagnetic substances the field strength B > > > H.
E.g.: Fe, Co and Ni.

Question 10.
Explain Ferrimagnetisms with suitable example.
Answer:
Ferrimagnetism is observed when the magnetic moments of the domains in the substance are aligned in parallel and anti parallel directions in unequal numbers.

• These are weakly attracted by magnetic field as compared to ferromagnetic substances.
• These lose ferrimagnetism on heating and becomes paramagnetic.

Question 11.
Explain Antiferromagnetism with suitable example.
Answer:
Substances like Mno showing anti-ferromagnetism having domain structure similar to ferromagnetic substance, but their domains are oppositely oriented and cancel out each others magnetic moment.

Question 12.
What are Tetrahedral voids ?
Answer:
The second layer spheres over the first layer arrangement, the spheres of second layer are placed in the depressions of the first layer. All the triangle voids of the first layer are covered by the spheres of second layer. These are called ‘Tetrahedral voids’.

Question 13.
What are Octahedral voids ?
Answer:
The triangular voids in the second layer are above the triangular voids in the first layer. Such voids are surrounded by six spheres and are called ‘Octahedral voids’.

Question 14.
What are n-type semiconductors ?
Answer:
Silicon and Germanium belong to IVA group and have four valence electrons. When these elements are doped with VA group like P or As which have 5 valence electrons some of lattice sites of Si are replaced by VA group element. Each VA group element forms four bonds with four Si atoms and fifth electron is extra and becomes delocalised. These delocalised electrons increase the conductivity. The increase in conductivity is due to negatively charged electrons. Hence it is called n – type semi conductor.

Question 15.
What are p-type semi conductors ?
Answer:
Silicon and Germaium when doped with IIIA group elements like B or Al which have only 3 valence electrons. These electrons are bonded to three silicon atoms and fourth valence electron place is vacant. It is called hole. Under the influence of electric field, electrons move towards positive electrode through holes. Hence this type of semi-conductors are called p – type semi conductors.

Question 16.
How many lattice points are there in one unit cell of face – centered tetragonal lattice ?
Answer:
In face centered’tetragonal unit cell
Number of face centered atoms per unit cell
= 6 face centered atoms × \(\frac{1}{2}\) atom per unit cell
6 × \(\frac{1}{2}\) = 3 atoms
∴ Total no. of lattice points = 1 + 3 = 4.

Question 17.
How many lattice points are there in one unit cell of body centered cubic lattice ?
Answer:
In body – centered cubic unit cell
The number of comer atoms per unit cell
= 8 comers × \(\frac{1}{8}\) per corner atom
= 8 × \(\frac{1}{8}\) = 1 atom
Number of atoms at body center = 1 × 1 = 1 atom
∴ Total no. of lattice points = 1 + 1 = 2.

Short Answer Questions

Question 1.
Calculate the efficiency of packing in case of a metal of simple cubic crystal.
Answer:
Packing efficiency in case of metal of simple cubic crystal:

The edge length of the cube
a = 2r. (r = radius of particle)
Volume of the cubic unit cell = a³ = (2r)³
= 8r³
∵ A simple cubic unit cell contains only one atom
The volume of space occupied = \(\frac{4}{3}\) πr³
∴ Packing efficiency
= \(\frac{\text { Volume of one atom }}{\text { Volume of cubic unit cell }}\) × 100
= \(\frac{4 / 3 \pi r^{3}}{8 r^{3}}\) × 100 = \(\frac{\pi}{6}\) × 100 = 52.36%.

Question 2.
Calculate the efficiency of packing in case of a metal of body centered cubic crystal.
Answer:
Packing efficiency in case of a metal of body centred cubic crystal:

in B.C.C. Crystal
\(\sqrt{3}\)a = 4r
a = \(\frac{4 \mathrm{r}}{\sqrt{3}}\)
In this structure total no. of atoms is ‘2’ and their volume = 2 × (\(\frac{4}{3}\)) πr³
Volume of the cube = a³ = (\(\frac{4}{\sqrt{3}}\)r)³

Question 3.
Describe the two main types of semiconductors and contrast their conduction mechanism.
Answer:
The solids which are having moderate conductivity between insulators and conductors are called semi conductors.

• These have the conductivity range from 10^-6 to 10⁴ Ohm^-1m^-1.
• By doping process the conductivity of semi conductors increases.
  E.g.: Si, Ge, crystal.

Semi conductors are of two types. They are :
1. Intrinsic semi-conductors : In case of semi-conductors, the gap between the valence band and conduction band is small. Therefore, some electrons may jump to conduction band and show some conductivity. Electrical conductivity of semi-conductors increases with rise in “temperature”, since more electrons can jump to the conduction band. Substances like silicon and germanium show this type of behaviour and are called intrinsic semi-conductors.

2. Extrinsic semi – conductors : Their conductivity is due to the presence of impurities. They are formed by “doping”.
Doping: Conductivity of semi-conductors is too low to be of pratical use. Their conductivity is increased by adding an appropriate amount of suitable impurity. This process is called “doping”.
Doping can be done with an impurity which is electron rich or electron deficient.

Extrinsic semi-conductors are of two types.
a) n-type semi-conductors : It is obtained by adding trace amount of V group element (P, As, Sb) to pure Si or Ge by doping.
When P, As, Sb (or) Bi is added to Si or Ge, some of the Si or Ge in the crystal are replaced by P or As atoms and four out of five electrons of P or As atom will be used for bonding with Si or Ge atoms while the fifth electron serve to conduct electricity.

b) p-type semi-conductors : It is obtained by doping with impurity atoms containing less electrons i.e., Ill group elements (B, Ai, Ga or In).
When B or AZ is added to pure Si or Ge, some of the Si or Ge in the crystal are replaced by B or AZ atoms and four out of three electrons of. B or AZ atom will be used for bonding with “Si” or Ge atoms while the fourth valence electron is missing is called electron hole (or) electron vacancy. This vacancy on an atom in the structure migrates from one atom to another. Hence it facilitates the electrical conductivity.

Question 4.
Derive Bragg’s equation. [A.P. & T.S. Mar. 17, 16; IPE Mar & May 15]
Answer:
Derivation of Bragg’s equation: When X-rays are incident on the crystal or plane, they are diffracted from the lattice points (lattice points may be atoms or ions or molecules). In the crystal the lattice points are arranged in regular pattern. When the waves are diffracted from these points, the waves may be constructive or destructive interference.

The 1^st and 2^nd waves reach the crystal surface. They undergo constructive interference. Then from the figure 1^st and 2^nd rays are parallel waves. So, they travel the same distance till the wave form AD. The second ray travels more than the first by an extra distance (DB + BC) after crossing the grating for it to interfere with the first ray in a constructive manner. Then only they can be in the same phase with one another. If the two waves are to be in phase, the path difference between the two ways must be equal to the wavelength (X) or integral multiple of it (nλ, where n = 1, 2, 3, ………..)
(i.e.,) nλ = (DB + BC) [where n = order of diffraction]
DB = BC = d sin θ [θ = angle of incident beam,]
(DB + BC) = 2d sin θ [d = distance between the planes]
nλ = 2d sin θ
This relation is known as Bragg’s equation.

Andhra Pradesh BIEAP AP Inter 2nd Year Chemistry Study Material 13th Lesson Organic Compounds Containing Nitrogen Textbook Questions and Answers.

AP Inter 2nd Year Chemistry Study Material 13th Lesson Organic Compounds Containing Nitrogen

Very Short Answer Questions

Question 1.
Write the IUPAC names of the following compounds and classify them into primary, secondary, and tertiary amines.
i) (CH₃)₃CHNH₂
ii) CH₃ (CH₂)₂ NH₂
iii) (CH₃CH₂)₂ NCH₃
Answer:
i) (CH₃)₃CHNH₂ :

IUPAC name : 2 – methyl 2 – propananine ^ – NH
It is a 1° – amine

ii) CH₃ (CH₂)₂ NH₂:

IUPAC name : 1 – Propananine
It is a 1° – amine

iii) (CH₃CH₂)₂ NCH₃

IUPAC name : N – Elthyl N – Methyl Ethanamine
It is a 3° – amine

Question 2.
Explain why ethylamine is more soluble in water, whereas aniline is not soluble.
Answer:
Elthyl amine is more soluble in water due to the presence of hydrogen bonding. Where are in case of aniline due to presence of bulky hydrocarbon part, the extent of hydrogen bonding is less and it is not soluble in water.

Question 3.
Why aniline does not undergo Friedel – Crafts reaction ?
Answer:
Aniline is a lewis base and AlCl₃ is a Lewis acid. In Friedal Craft’s reaction both of these combined to form a complex

Lewis box Lewisacid Due to formation of complex the electrophilic substitution tendency decreases in aniline and it does not undergo these reaction.

Question 4.
Gabriel Phthalimide synthesis exclusively forms primary amines only. Explain.
Answer:
Gabriel Phthalinide synthesis exclusively forms primary amines only.
Reason : In this reaction primary amines are formed without the traces of 2° (or) 3° amines.

Question 5.
Arrange the following bases in decreasing order of pK_b values. C₂H₅NH₂, C₆H₅NHCH₃, (C₂H₅)₂ NH and C₆H₅NH₂.
Answer:
The decreasing order of pK_b values.of gives amines is
C₆H₅NH₂ > C₆H₅NHCH₃ > C₂H₅NH₂ > (C₂H₅)₂NH

Question 6.
Arrange the following bases in increasing order their basic strength. Aniline. P – nitroaniline and P – toluidine.
Answer:
The increasing order of basic strength of given compounds is

Question 7.
Write equations for carbylamine reaction of any one aliphatic amine. [A.P.& T.S. Mar. 16]
Answer:
When Ethyl amine (1° – amine) reacts with chloro form in presence of alkali to form ethyl isocyanide.
CH₃ – CH₂ – NH₂ + CHCl₃ + 3KOH CH₃ – CH₂ – NC + 3KCl + 3H₂O

Question 8.
Give structures of A, B and C in the following reactions.

Answer:

A – Phenyl Cyanide B – Benzoic acid C – Benzamide

Question 9.
Accomplish the following conversions. [Mar. 14]
i) Benzoic acid to benzamide
ii) Aniline to P – bromoaniline.
Answer:
Conversion of benzoic acid to benzamide

ii) Conversion of Aniline to P – bromo aniline

Question 10.
Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?
Answer:
Aromatic 1° – amines cannot be prepared by Gabriel phthalinide synthesis beczause aryl halides do not undergo nucleophilic substitution with the an ion formed by phthalinide.

Short Answer Questions

Question 1.
Write the IUPAC names of the following compounds.
i) CH₃CH₂NHCH₂CH₂CH₃
ii) PhCH₂CN

Answer:
i) CH₃CH₂NHCH₂CH₂CH₃
N – Ethyl 1 – Propanamine

ii) PhCH₂CN
Phenyl Ethane nitrile (Benzyl cyanide)

Question 2.
Give one chemical test to distinguish between the following pairs of compounds.
i) Methylamine and dimethylamine
ii) Aniline and N.Methylaniline .
iii) Ethylamine and aniline
Answer:
i) Methyl amine (1° – amine) and dimethyl amine (2° – amine) are distinguished by iso cyanide test (or) Carbylamine (est. Methyl amine responds to carbylamine reaction to produce methyl isocyanide where as dimethyl amine does not respond to the iso cyanide test

ii) Aniline (1° – amine) and N.methyl (2° – amine) aniline are distinguished, by carbylamine test (or) isocyanide test. Aniline responds to carbyl amine test to give foul smelling phenyl iso cyanide where as N – methyl aniline does not responds to carbyl amine Test.

iii) Ethyl amine (1° – aliphafic amine) and aniline (1° – aromatic amine) are distinguished by Diazotisation reaction. Aniline under go diazotisation reaction to form benzene diazonium salt where as ethyl amine form highly unstable alkyl diazonium salt

Question 3.
Account for the following :

1. pK_b of aniline is more then of methylamine.
2. Reduction of alkylcyanide forms primary amine whereas alkyl isocyanide forms secondary amine.

Answer:

1. In aniline there exist conjugation between the electron pair on nitrogen and benzene ring and is less available for protonation than in nethyl amine.
   ∴ pK_b value of aniline is more than that of methylamine and aniline is less basic.
2. The reduction of alkyl cyanides forms 1°- amines. In alkyl cyanides alkyl group is attached to carbon atom of cyanide, Where as in alkyl iso cyanides alkyl group is attached to nitrogen atom of isocyanide. So reduction of alkyl isocyanide forms 2°- amines.
   

Question 4.
How do you prepare the following ?
i) N, N-Dimethyl proponamine from ammonia
ii) Propanamine from chloroethane
Answer:
i) Preparation of N, N – Di nethyl propanamine from ammonia : Chloro propane reacts with ammonia followed by the reaction of methylchloride to form N, N – Di methyl propananine.

ii) Preparation of propanamine from chloroethane : Chloro ethane reacts with KCN followed by the reduction forms propanamine

Question 5.
Compare the basicity of the following in gaseous and in a queous state and arrange them in increasing order of basicity.
Answer:
Givein compounds CH₃NH₂, (CH₃)₂NH, (CH₃)₃N and NH₃.
In the above compounds methly substituted ammonium ion gets stabilised due to dispersal of the positive charge by the +1 effect of the methyl group. Hence methyl amines are stronger bases than ammonia. Basic nature of amines increase with increase of methyl groups. This trend is followed in gaseous phase.
(CH₃)₃ N > (CH₃)₂ NH > CH₃ NH₂ > NH₃
In the aqueous phase the substituted ammonium cations get stabilised not only by electron releasing effect of the alkyl group but also by solvation with water molecules. Due to steric hinderance the basic strength of methyl amines in the aqueous state changed as follows
(CH₃)₂ NH > CH₃ NH₂ > (CH₃)₃ N > NH₃

Question 6.
How do you carryout the following conversions?
i) N – Ethylamine to N, N – Diethyl propanamine
ii) Aniline to Benzene suiphonamide
Answer:
Conversion of
i) N – Ethyl amine to N, N – Diethyl propanamine Ethyl amine reacts with ethyl chloride and propyl chloride to from N N – Di ethyl propanamine.

ii) Conversion of Aniline to Benzene sulphonamide : Aniline reacts with benzene sulphonyl chloride to form N – Phenyl benzene suiphonamide.
C₆H₅NH₂ + C₆H₅SO₂Cl → C₆H₅NHSO₂ C₆H₅ + HCl Phenyl benzene sulphonamide

Question 7.
Explain with a suitable example how benzene sulphonylchioride can distinguish primary secondary and tertiary amines.
Answer:
Benzene suiphonyl chloride is called Hinsbergs reagent. This is used to distinguish the 1°, 2°,. 3° – amines.
— with le – amine: Benzene suiphonyl chloride reacts with 1° amine and produce N – Alkyl benzene sulphonamide which is soluble in alkali.

—, with 2° – amine: Benzene suiphonyl chloride reacts with 2° – amine and produce N, N – DiaLkyl benzene sulphonamide which is insoluble in alkali

—, with 3° – amine : Benzene sulphonyl chloride does not react with benzene sulphonyl chloride.

Question 8.
Write the reactions of
i) aromatic and
ii) aliphatic primaiy amines with nitrous acid.
Answer:
i) Reaction of aromatic 1° – amine with nitrous acid : Aromatic 1° – amine react with , nitrous acid at low temperature (0 – 5°C) to form diazonium salts.

ii) Reaction of Aliphatic 1° – amine with nitrous acid : Aliphatic 1° – amine react with nitrous acid to form highly unstable diazonium salts which gives nitrogen gas and alcohols after decomposition.

Question 9.
Explain why amines are less acidic than alcohols of comaparable molecular masses.
Answer:
Amines are less acidic than alcohols of comparable molecular massey
Explaination : In alcohols the O – H bond is more polar than N – H bond of amines. Hence Amines releates H⁺ ion with more difficulty as compared to alcohol.

Question 10.
How do you prepare Ethyl cyanide and Ethyl isocyanide from a common alkylhalide ?
Answer:
Preparation of ethyl cyanide : Ethyl chloride reacts with aq. Ethanolic KCN to form Ethyl cyanide as a major product

Preparation of Ethyl isocyanide : Ethyl chloride reacts with aq. Ethanolic AgCN to form Ethyl iso cyanide as a major product

Long Answer Questions

Question 1.
An aromatic compound A’ on treatment with aqueous ammonia and heating forms compound B which on heating with Br₂ and KQH forms compound ‘C’ of molecular formula C₆H₇N. Write the structures and IUPAC names of compounds A, B and C.
Answer:
Given that an aromatic compound A on treatment with aq. NH₃ and heating forms compound ‘B’. Which on heating with Br₂ and KOH forms compound ‘C’ of molecular formula C₆H₇N.
1. From the above information ‘B is amide and ‘C’ is amine
2. Molecular formula of ‘C’ is C₆H₇N, So ‘C’ is Amiine (C₆H₅NH₂)
3. Compound A on treatment with aq. NH₃ forms B.
So ‘A’ is Benzoic acid (C₆H₅ – COOH)
and B’ is Benzamide (C₆H₅ – CONH₂)

Question 2.
Complete the following conversions.
i) CH₃NC + HgO → ?
ii) ? 2H₂O → CH₃NH₂ + HCOOH

Answer:

Question 3.
i) Write the structures of different isomeric amines corresponding to the molecular formula C₉H₁₃N.
ii) What reducing agents can bring out reduction of nitrobenzene?
iii) Write the product formed when benzyl chloride is reacted with ammonia followed by treatment with methyl and ethyl chlorides. Write the product
Answer:
i) Given compound molecular formula C₉H₁₃N
The structures of different isomeric amines corresponding to the above formula C₉H₁₃N

ii) The reducing agents that bring out the reduction of nitro benzene are :

1. H₂/Pd (or) Pt (or) Ni [Ethanol]
2. Sn + HCl (or) Fe + HCl
3. Li AlH₄
4. Zn + alc.KOH
5. Zn + NH₄Cl

iii) a) Benzyl chloride reacts with ammonia to form benzyl amine followed by the reaction with methyl chloride forms N, N – Dimethyl phenyl methanamine

b) Benzyl chloride reacts with ammonia to form benzyl amine followed by the reaction with Ethyl chloride form

Question 4.
i) Identify the amide and cyanide which on reduction with appropriate reducing agent gives n – butylamlne.
ii) Write the mechanism of Hoffmann bromamide reaction.
Answer:
i) a) Propyl cyanide on reduction gives n – Butylamine

ii) Hoffmann bromamide reaction : It is a simple way of converting an amide to an amine having one carbon atom less than the starting amide. The reaction is a rearrangement which is brought about by bromide in presence of alkali. It is believed to proceed through the steps shown below.

Question 5.
How do you make the following convertions ?
i) Chlorophenylmethane to phenylacetic acid
ii) Chlorophenylmethane to 2 – phenylethanamine.
Answer:

Question 6.
Identify the starting amide which gives p – methyl aniline on reaction with bromine and sodium hydroxide and write all the steps involved in the reaction. .
Answer:
P – methyl Acetanilide reacts with bromine and sodium hydroxide to form P – methyl aniline.

Question 7.
Explain why the order of basicity for methyl amine, N, N – dimethyl amine and N, N, N – tnmethyl amine changes in gasous and a aqueous medium.
Answer:
Given compounds
CH₃NH₂, (CH₃)₂NH, (CH₃)₃N and NH₃
In the above compounds methyl substituted, ammonium ion gets stabilised due to dispersal of the positive charge by the + 1 effect of the methyl group. Hence methyl amines are stronger bases than ammonia. Basic nature of amines increase with in increase of methyl groups. This trend is followed in gaseous phase.
(CH₃)₃ N> (CH₃)₂ NH > CH₃NH₂ > NH₃.
In the aqueous phase the substituted ammonium cations get stabilised not only by electron releasing effect of the alkyl group but; also by solvation with water molecules. Due to sterichindrance the basic strength of methyl amines in the aqueous state changed as follows
(CH₃)₂ NH > CH₃ NH₂> (CH₃)₃ N > NH₃

Question 8.
Write the equations involved in the reaction of Nitrous acid with Ethylamine and aniline.
Answer:
Reaction of Ethylamine with nitrous acid : Ethyl amine reacts with nitrous acid to form highly unstable diazonium salt which gives nitrogeñ gas and Ethyl alcohol after decomposition.

Reaction of Aniline with nitrous acid : Aniline reacts with nitrous acid at low temperatures (0- 5°C) to form diazomum salts. (Benzene diazonium salt)

Question 9.
Explain with equations how methylamine, N, N – dimethylamine and N, N, N – trimethylamine react with benzenesulphonyl chloride and how this reaction Is useful to separate these amines.
Answer:
Benzene suiphonyl chloride is called Hinsbergs reagent. This is used to distinguish the 1°, 2°, 3° – amines.
-. with 1°- amine : Benzene sulphonyl chloride reacts with 1°-. amine and produce N – Alkyl benzene sulphonamide which is soluble in alkali.

.- with 2° – amine: Benzene sulphonyl chloride reacts with 2° – amine and produce N, N – Dialkyl benzene sulphonamide which is insoluble in alkali

—, with 3° – amine: Benzene sulphonyl chloride does not react with benzene sulphonyl chloride.

Question 10.
Explain why aniline In strong acidic medium gives a mixture of Nitro anilines and what steps need to be taken to prepare selectively p – nitro aniline.
Answer:
In strong acidic medium anime under go nitration to form mixture of nitro animes. In strongly acidic medium aniline is protonated to form the anilinium ion which is metadirecting. So besides the ortho and para derivatives meta derivative also formed.

By protecting – NH₂ group by acetylation reaction with acetic an hydride the nitration reaction can be controlled and the – P – nitro derivative can be formed as major product.

Question 11.
i) Account for the stability of aromatic diazoniun ions when compared to aliphatic diazonium ions.
ii) Write the equations showing the conversion of aniline diazoniumchloride to
a) chlorobenzene, b) Iodobenzene and c) Bromobenzene
Answer:
i) —> Aliphatic diazonium salts which are formed from 1° – aliphatic amines are highly unstable and liberate nitrogen gas and alcohols.
—> Aromatic diazonium salts formed from 1° – aromatic amines are stable for a short time in solution at low temperatures (0 – 5°C). The stability of arene diazonium ion is explained on the basis of resonance.

ii) a) Conversion of aniline diazonium chloride to chloro benzene
C₆H₅N₂⁺ C₆H₅Cl + N₂
b) Conversion of aniline diazonium chloride to Iodo benzene
C₆H₅N₂⁺Cl^– + KI → C₆H₅I + N₂ + KCl
c) Conversion of aniline diazonium chloride to Bromo benzene
C₆H₅N₂⁺Cl^– C₆H₅Br + N₂

Question 12.
Complete the following conversions : Aniline to
i) Fluorobenzene
ii) Cyanobenzene
iii) Benzene and
iv) Phenol
Answer:
i) Aniline to Fluorobenzene

ii) Aniline to cyano benzene

iii) Aniline to Benzene

iv) Aniline to phenol

Question 13.
Explain the following name reactions: [A.P. Mar. 18]
i) Sandmeyer reaction
ii) Gatterman reaction
Answer:
i) Sandmeyer reaction: Formation of chioro benzene, Brono benzene (or) cyano benzene from benzene diazonium salts with reagents Cu₂Cl₂/HCl, Cu₂Br₂/HBr, CuCN/KCN is called sandmayers reaction.

ii) Gatterman reaction : Formation of chloro benzene, Bromobenzene from benzene diazonium salts with reagents Cu/HCl, Cu/HBr is referred as gatterman reaction.

Question 14.
Write the steps involved in the coupling of Benzene diazoniumchloride with aniline and phenol.
Answer:
Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the diazonium salt to form P-hydroxyazobenzene. This type of reactionsis known as coupling reactions. Similarly the reaction of diazonium salt with aniline yields P – amino azobenzene.

Question 15.
Write the equations involved in the conversion of acetamide and propanaldehydeoxime to methyl cyanide and ethyl cyanide respectively.
Answer:

Textual Examples

Question 1.
Write chemical equations for the following reactions:
i) Reaction of ethanolic NH₃ with C₂H₅Cl.
ii) Ammonolysis of benzyl chloride and reaction of amine so formed with two moles of CH₂Cl.
Solution:

Question 2.
Write chemical equations for the following Conversions:
i) CH₃ – CH₂ – Cl into CH₃ – CH₂ – CH₂ – NH₂
ii) C₆H₅ – CH₂ – Cl into C₆H₅ – CH₂ – CH₂ – NH₂
Solution:

Question 3.
Write structures and IUPAC names of
i) the amide which gives propanamine by Hoffmann bromarnide reaction.
ii) the amine produced by the Hoffmann degradation of benzamide.
Solution:
i) Propanamine contains three carbons. Hence, the amide molecule must contain four carbon atoms. Structure and IUPAC name of the starting amide with four carbon atoms are given below:

ii) Benzamide is an aromatic amide containing seven carbon atoms. Hence, the amine formed from benzamide is aromatic primary amine containing six carbon atoms.

Question 4.
Arrange the following in decreasing order of their basic strength:
C₆H₅NH₂, C₂H₅NH₂, (C₂H₅)₂ NH, NH₃. [T.S. Mar.’19]
Solution:
The decreasing order of basic strength of the above amines and ammonia follows the following order:
(C₂H₅)₂NH > C₂H₅NH₂ > NH₃ C₆H₅NH₂
Amines also react with benzoyl chloride (C₆H₅COCl). This reaction is known as benzoylation.
CH₃NH₂ + C₆H₅COCl → CH₃NHCOC₆H₅ + HCl
Methanamine Benzoyl chloride N – Methylbenzamide
What do you think is the product of the reaction of amines with carboxylic acids ? They form salts with amines at room temperature.

Question 5.
How will you convert 4 nitrotoluene to 2 – bromobenzoic acid?
Solution:

Intext Questions

Question 1.
Classify the following amines as primary, secondary or tertiary.

iii) (C₂H₅)₂CHNH₂
iv) (C₂H₅)₂NH
Solution:
i) Primary
ii) Tertiary
iii) Primary
iv) Secondary.

Question 2.
i) Write the structures of different isomeric amines corresponding to the molecular – formula, C₄H₁₁N.
ii) Write IUPAC names of all the isomers.
iii) What type of isomerism is exhibited by different pairs of amines ?
Solution:
i) and ii) Eight isomers of C₄H₁₁N are :

iii) Isomerism exhibited by different amines are:
a) Chain isomers : i.e., have different carbon chains (a) and (b), (c) and (d).
b) Position isomers : i.e., functional group occupy different positions, (b) and (c), (b) and (d), (a) and (d).
e) Metamers: i.e., different alkyl groups are attached to the same functional group, (e) and (0, (g) and (e).
d) Functional isomers : i.e., have different functional groups. All the three categories (1°, 2° and 3°) of amines are the functional isomers of each other.

Question 3.
How will you convert
i) benzene into aniline ?
ii) benzene into N, N-dimethylaniline ?
iii) Cl-(CH₂)₄-Cl into hexan-1, 6-diamine ?
Solution:
i) Benzene into aniline:

ii) benzene into N, N-dimethylaniline

iii) Cl-(CH₂)₄-Cl into hexan-1, 6-diamine

Question 4.
Arrange the following in increasing order of their basic strength.
i) C₂H₅NH₂, C₆H₅NH₂, NH₃, C₆H₅CH₂NH₂ and (C₂H₅)₂NH
ii) C₂H₅NH₂, (C₂H₅)₂NH, (C₂H₅)₃N, C₆H₅NH₂
iii) CH₃NH₂, (CH₃)₂NH, (CH₃)₃N, C₆H₅NH₂, C₆H₅CH₂NH₂
Solution:
i) C₂H₅NH₂ < NH₃ < C₆H₅CH₂NH₂ < C₆H₅NH₂ < (C₂H₅)₂NH
ii) C₆H₅NH₂ < C₂H₅NH₂ < (C₂H₅)₃N < (C₂H₅)₂NH
iii) C₆H₅NH₂ < C₆H₅CH₂NH₂ < (CH₃)₃N< CH₃NH₂ < (CH₃)₂NH

Question 5.
Complete the following acid-base reactions and name the products.
i) CH₃CH₂CH₂NH₂ + HCl →
ii) (C₂H₅)₃N + HCl →
Solution:

Question 6.
Write reactions of the final alkylation product of aniline with excess of methyl iodide in the presence of sodium carbonate solution.
Solution:
Hofmann’s ammonolysis reaction: In the presence of excess methyl iodide, aniline (primary amine) forms quartemary ammonium salt.

Question 7.
Write the chemical reaction of aniline with benzoyl chloride and write the name of the product obtained.
Solution:

Question 8.
Write the structures of different isomers corresponding to the molecular formula C₃H₉N. ‘ Write IUPAC names of the isomers which will liberate nitrogen gas on treatment with nitrous acid.
Solution:
C₃H₉N has four isomers :

Question 9.
Convert :
(i) 3-methyl aniline into 3-nitrotoluene.
(ii) anline into 1, 3, 5-tribromobenzene.
Solution:
i) 3-methyl aniline into 3-nitrotoluene.

(ii) Anline into 1, 3, 5-tribromobenzene.

Andhra Pradesh BIEAP AP Inter 2nd Year Chemistry Study Material Lesson 12(b) Aldehydes, Ketones, and Carboxylic Acids Textbook Questions and Answers.

AP Inter 2nd Year Chemistry Study Material Lesson 12(b) Aldehydes, Ketones, and Carboxylic Acids

Very Short Answer Questions

Question 1.
Arrange the following compounds in increasing order of their property indicated.

1. Acetaldehyde, Acetone, Methyl t. butyl ketone reactivity towards HCN.
2. Floroacetic acid, monochloroacetic acid, Acetic acid and Dichloroacetic acid (acid strength)

Answer:

1. Due to the presence of groups around the carbonyl group the reactivity of a compound depends on the steric hindrance.
   Greater the steric hindrance, less will be the reactivity of the compound. Reactivity towards HCN is in the following order.
   Methyl tertiary butyl ketone < Acetone < Acetaldehyde
2. Acid strength of given compounds is Dichloro acetic acid > fluoro acetic acid > chloro acetic acid > acetic acid.

Question 2.
Write the reaction showing a-halogenation of carboxylic acid and give its name.
Answer:
Carboxylic acids having a-hydrogens are halogenated at the a-position on treatment with chlorine or bromine in presence of small amount of red phosphorous to give a-halo carboxylic acids.
This reaction is named as Hell-volhard – Zelinsky (HvZ) reactions

Question 3.
Although phenoxide ion has more number of resonating structures thancarboxylate ion carboxylic acid is a stronger acid than phenol. Why ?
Answer:

• Phenoxide ion has non-equivalent resonance structures in which the negative charge is at the less electronegative carbon atom.
• The negative charge is delocalised over two electronegative oxygen atoms in carboxylate ion whereas in phenoxide ion the negative charge less effectively delocalised over one oxygen atom and less electronegative carbon atoms.
  

Question 4.
How do you distinguish acetophenone and benzophenone?
Answer:
On idoform test Acetophenone gives positive, where as benzophenone (C₆H₅COC₆H₅) does not

Question 5.
Explain the position of electrophilic substitution In benzolc acid.
Answer:
Benzoic acid undergo electrophilic substitution reactions in which carboxyl group acts as a deactivating and meta dirécting group.

Question 6.
Write equations showing the conversion of
i) Acetic acid to Acetyl chloride
ii) Benzoic acid to Benzamide
Answer:
i) acetic acid reacts with PCl₃ (or) PCl₅ (or) SOCl₆ to form acetyl chloride

ii) Benzoic acid reacts with ammonia to form benzamide

Question 7.
An organic acid with molecular formula C₈H₈O₂ on decarboxylation forms Toluene. Identify the organic acid.
Answer:
The organic acid is phenyl acetic acid

Question 8.
List the reagents needed to reduce carboxylic acid to alcohol.
Answer:
The Reagents required to reduce carboxylic acid to alcohol are

1. LiAlH₄/Ether (or) B₂H₆
2. H₄O⁺

Question 9.
Write the mechanism of esterification.
Answer:
Mechanism of esterification of carboxylic acids : The esterification of carboxylic acids with alcohols is a kind of nucleophilic acyl substitution. Protonation of the carbonyl oxygen activates the carbonyl group towards nucleophilic addition of the alcohol. Proton transfer in the tetrahedral intermediate converts the hydroxyl group into – ⁺OH₂ group, which, being a better leaving group, is eliminated as neutral water molecule. The protonated ester so formed finally loses a proton to give the ester.

Question 10.
Compare the acidic strength of acetic acid, Chloroacetic acid, benzoic acid and Phenol. [Mar. 14]
Answer:
Benzoic acid (C₆H₅COOH) > Chloro acetic acid (ClCH₂COOH) > Acetic acid (CH₃COOH) > Phenol (C₆H₅OH)

Short Answer Questions

Question 1.
Write the equations of any aldehyde with Fehlings reagent.
Answer:
Fehling’s reagent is mixture of two solutions Fehling’s A and Fehlings B.
Fehling’s A – aq. CuSO₄ solution
Fehling’s B – Sodium potassium tartarate (Rochelle salt)
Acetaldehyde reacts with Fehlings .eagent and gives a redbrown ppt.
Reaction:
CH₃ – CHO + 2CU⁺² + 5OH^– → RCOO^– + CU₂O + 3H₃O (Red – brown ppt)

Question 2.
What is Tollens reagent? Explain Its reaction with Aldehydes.
Answer:
Tollens Reagent : Freshly prepared ammonicai silver nitrate solution is called Tollens reagent.

On warming an aldehyde with Tollens reagent a bright silver mirror is produced due to formation of silver metal.
R – CHO + 2 [Ag(NH₃)₂]⁺ + 3OH^– → RCOO^– + 2Ag + 2H₂O + 4NH₃

Question 3.
Write the oxidation products of : Acetaldehyc, Acetone and Acetophenone.
Answer:
a) Acetaldehyde under goes oxidation to foim acetic acid.

b) Acetone undergoes oxidation to form acetic acid

c) Acetophenone undergoes oxidation to form benzoicacid and chloroform

Question 4.
Explain why Aldehydes and ketones undergoes nucleophilic addition while alkenes undergoes electrophilic addition though both are unsaturated compounds.
Answer:
The carbon – oxygen double bond in carbonyl compounds is polarised due to higher electronegativity of oxygen relative to carbon. Hence the carbonyl carbon is an electrophilic and carboxyl oxygen is a nucleophilic centre. So aldehydes, ketones undergoes nucleophilic addition reaction.

Alkenes contain which is a source of electron density so electrophiles add no to C = C to give addition products. Hence alkenes undergo electrophilic addition reaction.

Question 5.
Write the IUPAC names of the following:
i) CH₃CH₂CH(Br) CH₃COOH
ii) Ph. CH₃COCH₃COOH
iii) CH₃.CH (CH₃) CH₂COOC₂H₅
Answer:

Question 6.
Arrange the following In the increasing order of their acidic strength:
Benzolc acid, 4 – Methoxybenzoic acid, 4 – Nitrobenzoic acid and 4 – Methylbenzoic acid.
Answer:
Electron donating group (-OCH₃) decreases the acidic strength where as electron withdrawing group (NO₂) increases the same.
Increases order of acidic strength is:
4-Methoxy benzoic acid < benzoic acid < 4-nitrobenzoic acid < 3, 4-dinitro benzoic acid.

Question 7.
DescrIbe the following: .
i) Cross aldol condensation
ii) Decarboxylation
Answer:
i) Cross Aldol Condensation : When aldol condensation ¡s earned out between two different aldehydes and (or) ketones, it is called cross aldol condensation.

If both the reactants contain α-hydrogen atoms, it gives a mixture of four products.

Ketones can also be used as one component in the cross aldol reactions

ii) Decarboxylatlon : Carboxylic acids lose carbon dioxide molecule to produce hydrocarbons on heating their sodium salts with sodalizne (a mixutre of NaOH & CaO in ratio 3 : 1)
.-, This reaction is called decarboxylation

Question 8.
ExplaIn the role of electron withdrawing and electron releasing groups on the acidity of carboxylic acids.
Answer:

• Electron with drawing groups increase the acidity of carboxylic acids by stabilising the conjugate base through decocalisation of the negative charge by inductive effect.
• Electron donating groups decreases the äcidity of carboxylic acids by destabilising the conjugate base.
  
  Eg : Cl^– is a electron with drawing group acidic strength order in case of chloro acetic acids
  CCl₃COOH > CHCl₂COOH > CH₂ClCOOH > CH₃COOH

Question 9.
Draw the structures of the following derivatives:
i) Acetaldehyde dimethyl acetal
ii) The ethylene ketal of hexan-3-one
iii) The methyl hemiacetal of formaldehyde.
Answer:
The structures of following are
i) Acetaldehyde dimethyl acetal

ii) Ethylene Ketal of hexan-3-one

iii) Methyl hemiacetal of formaldehyde

Question 10.
An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It doesnot reduce Tollens’ reagent but forms sodium hydrogensulphite adduct and gives +ve iodoform test. On vigorous oxidation forms ethanoic and propanoic acids. Write the possible structure of the compound.
Answer:
Step : 1 To determine the molecular formula of the compound.

Emperical formula of the given compound = C₅H₁₀O
Molecular formula = n × (emperical formula)
Where n = \(\frac{\text { Molecular mass of the compound }}{\text { Emperical formula mass of compound }}\)
Given, molecular mass = 86
Emperical formula mass of C₅H₁₀O = (12 × 5) + (10 × 1) + 16 = 60 + 10 + 16 = 86
n = \(\frac{86}{86}\) = 1
Molecular formula = 1 × (C₅H₁₀O)
∴ Molecular formula = C₅H₁₀O

Long Answer Questions

Question 1.
Explain the following terms. Give an example of the reaction in each case. [A.P. Mar. 18]
i) Cyanohydrin
ii) Acetal
iii) Semicarbazone
iv) Aldol
v) Hemiacetal
vi) Oxime
Answer:
i) Cyanohydrin
Aldehydes and ketones react withk hydrogen cyanide (HCN) forms addition products called (or) known as cyanohydrins.

ii) Acetal
In the presence of dry HCl gas, an aldehyde reacts with two equivalents of a monohydric alchol forms gem-dialkoxy compounds are known as acetals.
—> In acetal two alkoxy groups are present on the terminal C-atom.

iii) Semicarbazone
Aldehydes/ketones react with semicarbazide forms certain compounds called as senilcarbazones.
For example:

iv) Aldol
When an aldehyde ((or) ketone) having at least one a-hydrogen atom undergo a reaction in the presence of dilute alkali as catalyst to form aldol (or) β- hydroxy aldehydes ((or) ketals in case of ketones), the reaction is called aldol condensation.
For example:

v) Hemiacetat : In the presence of dry HCl gas an aldehyde reacts with one molecule of a monohydric alcohol forms gem-alkoxy alcohols. These are known as hemiacetals.
For example:

vi) Oxime: In weak acidic medium, an aldehyde ketone reacts with hydroxylamine forms products which are known as oxims.

Question 2.
Name the following compounds according to IUPAC system of nomenclature:
i) CH₃CH(CH₃)CH₂CH₂CHO
ii) CH₃CH₂COCH (C₂H₅)CH₂CH₂Cl
iii) CH₃CH = CHCHO
iv) CH₃COCH₂COCH₃
Answer:
IUPAC names of following

Question 3.
Draw the structures of the following compounds.
i) 3-Methylbutanal
ii) p-Nitropropiophenone
iii) p-Metylbenzaldehyde
iv) 3-Bromo-4-phenylpentanoic acid
Answer:
i) 3 – Methyl butanal

ii) p-Nitropropiophenone

Question 4.
Write the IUPAC names of the following ketones and Aldehydes. Wherever possible, give also common names.
i) CH₃CO(CH₂)₄ CH₃
ii) CH₃CH₂CHBrCH₂CH (CH₃)CHO
iii) CH₃(CH₂)₅CHO
iv) PhCH = CHCHO
v)
vi) PhCOPh
Answer:
i) CH₃CO(CH₂)₄ CH₃

IUPAC Name: Heptan-2-one
Common Name: Methnyl n-pentyl ketone

ii) CH₃CH₂CHBrCH₂CH (CH₃)CHO

IUPAC Name : 4 – bromo – 2 – methyl hexanal
Common Name : γ – bromo – α – methyl caproaldehyde

iii) CH₃(CH₂)₅CHO

IUPAC Name: Heptanal
Common Name i n – heptyi aldehyde

iv) Ph – CH =CH – CHO

IUPAC Name : 3 – Phenyl Prop-2-en-1-al
Common Name: β – phenyl acrolein

v)
IUPAC Name: Cyclopentane Carbaldehyde

vi) PhCOPh

IUPAC Name : Diphenyl methanone
Common Name : Benzophenone

Question 5.
Draw the structures of the following derivatives.
i) The 2, 4 – dinitrophenylhydrazone of benzaldehyde
ii) Cyclopropanone oxime
iii) Acetaldehyde hemiacetal
iv) The Semicarbazone of cyclobutanone
Answer:
i) The 2, 4 – dinitro phenyl hydrazone of benzaldehyde :

ii) Cyclopropanone oxime

iii) Acetaldehyde hemiacetal

iv) The Semicarbazone of cyclobutanone

Question 6.
Predict the products formed when Cyclohexanecarbaldehyde reacts with following reagents.
i) PhMgBr and then H₃O⁺
ii) Tollens reagent
iii) Semicarbazide and weak acid
iv) Zinc amalgam and dilute HCl
Answer:
The products are formed when cyclohexane carbaldehyde reacts with following.
i) Ph MgBr and the H₃O⁺

ii) Tollens reagent

iii) Semicarbazide and weak acid

iv) Zinc amalgam and dilute HCl

Question 7.
Which of the following compounds would Undergo aldol condensation ? Write the structures of the products expected.
i) 2-Methylpentanal
ii) 1-Phenylpropanone
iii) Phenyl acetaldehyde
iv) 2,2 – Dimethylbutanal
Answer:
Compounds having one (or) more a-H atoms undergo aedol condensation.
So from above only first three compounds having α-H atoms. Therefore they undergo aldol condensation. They are namely

1. 2-methyl Pentanal
2. 1 – Phenyl propanone
3. Phenyl acetaldehyde

i) 2 – Methyl Pentanal


ii) 1 – Phenyl propanone

iii) Phenyl acetaldehyde

Question 8.
An organic compound A(C₉H₁₀O) forms 2, 4-DNP derivative, reduces Tollens’ reagent and undergoes Cannizaro reaction. On vigorous oxidation it gives 1, 2-benzene dicarboxylic acid. Identify the compound.
Answer:

• The compouhd having molecular formula C₉H₁₀O forms a 2, 4 – DNP derivative and reduces Tollen’s reagent. So it is an aldehyde.
• It undergoes cannizaro reaction, so the aldehyde group should be directly attached to the benzene ring.
• On vigorous oxidation it gives 1,2- benzene dicarboxylic acid, so it should be an ortho substituted benzaldehyde. For molecular formula C₉H₁₀O, the possibility is only O-ethyl benzaldehyde.
• The equations for all reactions are given below.
  
  

Question 9.
How do you distinguish the following pairs of compounds ?
i) Propanal and propanone
ii) Acetophenone and benzophenone
iii) Phenol and benzoic acid
iv) Pentan-2-one and Pentan-3-one
Answer:
i) Propanal and Propanone
On idoform test propanone responds, but absence of CH₃CO – group in propanal (CH₃CH₂CHO) it does not respond.

ii) Acetophenone and benzophenone
Acetophenone gives positive idoform test whereas benzophenone (C₆H₅COC₆H₅) does not

iii) Phenol and benzoic acid
Benzoic acid reacts with sodium bicarbonate to produce effervescences of carbon dioxide where as phenol (C₆H₅OH) does not

iv) Pentan-2-one and Pentan – 3 – One
On idoform test Pentan – 2 – One-responds whereas Pentan – 3 – one (C₂H₅ COC₂H₅) does not

Question 10.
How are the following conversions carried in not more than two steps ?
i) Ethanol to 3-hydroxybutanal
ii) Bromobenzene to 1-Phenylethanol
iii) Benzaldehyde to ± Hydroxyphenylacetic acid
iv) Benzaldehyde to benzophenone
Answer:
i) Ethanol to 3-hydroxybutanal

iv) Benzaldehyde to benzophenone

Question 11.
Describe the following. [A.P. & T.S. Mar. 19, 16] [A.P. Mar. 18]
i) Acetylation
ii) Cannizaro reaction
iii) Cross aldol condensation
iv) Decarboxylation
Answer:
i) Acetylation : When active hydrogen atom of alcohol, phenol (or) an amine is replaced by acetyl (CH₃CO^–) group to form corresponding ester (or) amide, the reaction is known as acetylation.

Reagents used are acid chloride (or) acid anhydride in presence of a base like pyridine (or) dimethylaniline.
For example :

ii) Cannizaro reaction: On treating with concentrated alkali, aldehydes which do not have any α – hydrogen atom, undergo self oxidation and reduction (disproportionation) reaction.
This reaction is called cannizaro reaction.

As a result, one molecule of aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.
For example:

iii) Cross aldol condensation: When aldol condensation is carried out between two different aldehydes and (or) ketones, it is called cross aldol condensation.

If both the reactants contain a – hydrogen atoms, it gives a mixture of four products.

Ketones can also be used as one component in the cross aldol reactions

iv) Decarboxylation
Carboxylic acids lose carbon dioxide molecule to produce hydrocarbons on heating their sodium salts with sodalime (a mixutre of NaOH & CaO in ratio 3: 1). This reaction is called decarboxylation.

Question 12.
Complete each synthesis by giving the missing starting material, reagent or product.

Answer:

Question 13.
Explain how methyl ketones are distinguished from other ketones. Write the equations showing it.
Answer:
Oxidation of methyl ketones by haloform reactIon : Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) are oxidisedby sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform. This oxidation does not affect a carbon-carbon double bond, If present in the molecule. lodoform reaction with sodium hypoiodite is also used for detection of CH₃CO group or CH₃CH(OH) group which produces CH₃CO group on oxidation.

Question 14.
Write the equations showing the conversion of the following along with reagents.
i) 1-phenyipropane to Benzoic acid
ii) Benzamide to Benzoic acid
iii) Ethyl butanoate to Butanoic acid.
Answer:
i)

Question 15.
Write the products and reagents needed for the below given conversions
i) 3-Nitrobromobenzene to 3-Nitrobenzoic acid
ii) 4-Methyl’acetophenone to Benzene- 1-4-dicarboxylic acid
Answer:
i) 3-Nitrobromobenzene to 3-Nitrobenzoic acid:

ii) 4-Methyl’acetophenone to Benzene- 1-4-dicarboxylic acid

Textual Examples

Question 1.
Give names of the reagents ot bring about the following transformations:

1. Hexan – 1 – ol to hexanal
2. Cyclohexanol to cyclohexanone
3. p – Fluorotoluene to p – fluorobenzaldehyde
4. Ethanenitrile to ethanal
5. Allyl alcohol to propanal
6. But-2-ene to ethanal

Solution:

1. C₅H₅NH⁺ CrO₃Cl^– (PCC)
2. K₂Cr₂O₇ in acidic medium
3. CrO₃ in the presence of acetic anhydride/1. CrO₂Cl₂₅ 2. HOH
4. (Diisobutyl) aluminiinn hydride (DIBAL-H)
5. PCC
6. O₃/H₂O-Zn dust

Question 2.
Arrange the following compounds in the increasing order of their boiling points:
CH₃CH₂CH₂CHO, CH₃CH₂CH₂CH₂OH, H₅C₂-O-C₂H₅, CH₃CH₂CH₂CH₂CH₃
Solution:
The molecular masses of these compounds are in the range of 72 to 74. Since only butan-1- ol molecules are associated due to extensive intermolecular hydrogen bonding, therefore, the boiling point of butan-l-ol would be the highest. Butanal is more polar than ethoxyethane. Therefore, the intermolecular dipole-dipole attraction is stronger in the former. n-Pentane molecules have only weak vander Waals forces. Hence increasing order of boiling points of the given compounds is as follows :
CH₃CH₂CH₂CH₂CH₃ < H₅C₂-O-C₂H₅ < CH₃CH₂CH₂CHO < CH₃CH₂CH₂CH₂OH

Question 3.
Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal ? Explain your answer.
Solution:
The carbon atom of the carbonyl group of benzaldehyde is less electrophilic them carbon . atom of the carbonyl group present in propanal. The polarity of the carbonyl group is reduced in benzaldehyde due to resonance as shown below and hence it is less reactive than propanal.

Question 4.
An organic compound (A) with molecular formula C₈H₈O forms an orange-red precipitate with 2,4 – DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide. It neither reduces Tollens or Fehlings reagent, nor does it decolourise bromine water or Baeyer’s reagent. On drastic oxidation with chromic acid, it gives a carboxylic acid (B) having molecular formula C₇H₆O₂. Identify the compounds (A) and (B) and explain the reactions involved.
Solution:
(A) forms 2, 4 – DNP derivative. Therefore, it is an aldehyde or a ketone. Since it does not reduce Tollens or Fehling’s reagent, (A) must be a ketone. (A) responds to iodoform test. Therefore, it should be a methyl ketone. The molecular formula of (A) indicates high degree of unsaturation, yet it does not decolourise bromine water or Baeyers reagent. This indicates the presence of unsaturation due to an aromatic, ring.

Compound (B), being an oxidation product of a ketone should be a carboxylic acid. The molecular formula of (B) indicates that it should be benzoic acid and compound (A) should, therefore, be a monosubstituted aromatic methyl ketone. The molecular formula of (A) indicates that it should be phenyl methyl ketone (acetophenone). Reactions are as follows:

Question 5.
Write chemical reactions to affect the following transformations :
i) Butan-1-ol to butanoic acid
ii) Benzyl alcohol to phenylethanoic acid
iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid
iv) 4 – Methylacetophenone to benzene – 1, 4 – dicarboxylic acid
v) Cyclohexene to hexane-1, 6 – dioic acid
vi) Butanal to butanoic acid.
Solution:

Intext Questions

Question 1.
Classify the following as primary, secondary and tertiary alcohols:


Answer:
Primary alcohols (1), (ii), (iii)
Secondary alcohols (iv) and (v)
Tertiary alcohols (vi)

Question 2.
Identify allylic alcohols In the above examples.
Answer:
Allylic alcohols (ii) and (vi)

Question 3.
Name of the following compounds according to IUPAC system.

Solution:
i) 3-Chloromethyl – 2 isopropylpentan – 1 – ol
ii) 2, 5 – Dimethylhexane – 1, 3 – diol
iii) 3 – Bromocyclohexanol
iv) Hex- 1 -en-3-ol
v) 2-Bromo~3-methylbut-2-en-1-ol

Question 4.
Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanal ?

Solution:

Question 5.
Write the structures of the products of the following reactions :

Solution:

Question 6.
Predict the major product of acid catalysed dehydration of
i) 1 – methylcyclohexanol and
ii) butan – 1 – ol
Solution:
i) 1 – Methylcyclohexene
ii) A mixture of but-1-ene and but-2-ene. But-1-ene is the major product formed due to rearrangement to give secondary carbocation.

Question 7.
Write the reactions of Williamson synthesis of 2-ethyoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-ol.
Solution:

Question 8.
Which of the following Is an appropriate set of reactants for the preparation of 1 – methoxy-4-nltrobenzene?

Solution:
ii)

Question 9.
Predict the products of the following reactions:

Solution:

Question 10.
Write the structures of the following compounds.
i) α-Methoxypropionaldehyde
ii) 3- Hydroxybutanal
iii) 2-Hydroxycyclopentane carbaldehyde
iv) 4-Oxopentanal
v) Di-Sec. butyl ketone
vi) 4 – Fluoroacetophenone
Solution:

Question 11.
Write the structures of products of the following reactions;

Solution:

Question 12.
Arrange the following compounds in increasing order of their boiling points.
CH₃CHO, CH₃CH₂OH, CH₂OCH₃, CH₃CH₂CH₃
Solution:
CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CHO < CH₃CH₂OH

Question 13.
Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions.

1. Ethanal, Porpanal, Propanone, Butanone.
2. Benzaldehyde, p – Toualdehyde, p – Nitrobenzaldehyde, Acetophenone.

Solution:

1. Butanone < Propanone < Propanal < Ethanal
2. Acetophenone < p – Touladehyde, Benzaldehyde < p – Nitgrobenzaldehyde.
   Hint: Consider steric effect and electronic effect.

Question 14.
Predict the products of the following reactions :


Solution:

Question 15.
Give the IUPAC names of the following compounds:
i) Ph CH₂CH₂COOH
ii) (CH₃)₂C = CHCOOH

Solution:
i) 3-Phenylpropanoic acid
ii) 3 – Mehtylbut-2-enoic acid
iii) 2-Metylcyclopentanecarboxylicacid
iv) 2, 4, 6 – Trinitrobenzoic acid

Question 16.
Show how each of the following compounds can be converted to benzoic acid.
i) Ethylbenzene
ii) Acetophenone
iii) Bromobenzene
iv) Phenylethene (Styrene)
Solution:

Question 17.
Which acid of each pair shown here would you expect to be stronger?
i) CH₃CO₂H or CH₂FCO₂H
ii) CH₂FCO₂H or CH₂ClCO₂H
iii) CH₂FCH₂CH₂CO₂H or CH₃CHFCH₂CO₂H

Solution:
i) CH₃COOH
ii) CH₂FCOOH
iii) CH₃CHFCH₂COOH
iv)

Andhra Pradesh BIEAP AP Inter 2nd Year Chemistry Study Material 11th Lesson Haloalkanes And Haloarenes Textbook Questions and Answers.

AP Inter 2nd Year Chemistry Study Material 11th Lesson Haloalkanes And Haloarenes

Very Short Answer Questions

Question 1.
Write the structures of the following compounds.
i) 2-chloro-3-methylpentane,
ii) 1-Bromo-4-sec-butyl-2-methylbenzene.
Answer:
i) 2-chloro-3-methylpentane
Structure :

ii) 1-Bromo-4-sec-butyl-2-methylbenzene.
Structure :

Question 2.
Which one of the following has highest dipole moment ?
i) CH₂Cl₂
ii) CHCl₃
iii) CCl₄
Answer:
CH₂Cl₂ has high dipole moment (μ = 1.62 D) among the three alkyl halides.
Reason: The total of two C – Cl dipole moments is reinforced by the total of two C-H bonds.
CCl₄ has zero dipole pioment. CHCl₃ has 1.03 D dipole moment due to presence of C-H bond.

Question 3.
What are ambident nucleophiles ?
Answer:
Ambident nucleophiles: The nucleophiles which are able to attack at two (or) more different sites are called ambident nucleophiles.
Eg.: Alkyl halides react with AgCN to form alkyl cyanide and isocyanides.

Question 4.
Write the isomers of the compound having molecular formula C₄H₉Br.
Answer:
Compound having molecular formula C₄H₉Br has five isomers.

Question 5.
Which compound in each of the following pairs will react faster in S_N² reaction with -OH?
(i) CH₃Br or CH₃I
(ii) (CH₃)₃CCl or CH₃Cl
Answer:
i) CH₃ – I reacts faster in SN² – reaction with OH than CH₃ – Br.
Reason: The bond dissociation enthalpy of C -1 bond (234 KJ/mole) is less than that of (-Br bond (293 KJ/mole).

ii) CH₃ – Cl reacts faster in S_N2-reaction with -OH than-(CH₃)₃C-Cl.
Reason: The order of reactivity of alkyl halides in S_N2-reactions is l°-alkyl halide > 2°- alkyl halide > 3°-alkyl halide.
Due to high steric hindrance in 3°-alkyl halide i.e., (CH₃C – Cl. It is less reactive towards S_N²-reaction, whereas in case of CH₃-Cl (1°-alkyl halide) less steric hindrance observed. So, it is high reactive towards S_N²-reactions.

Question 6.
Explain why the alkyl halides though polar are immiscible with water.
Answer:
Alkyl halides are polar but these do not dissolve in water i.e., immiscible in water.
Reason : Among water molecules strong inter molecular hydrogen bonding is present. This hydrogen bond is difficult to be broken by alkyl halides.

Question 7.
Out of C₆H₅CH₂Cl and C₆H₅CHClC₆H₅, which is more easily hydrolysed aqueous KOH ?
Answer:
Out of C₆H₅CH₂Cl and C₆H₅CHClC₆H₅ the 2^nd one i.e., C₆H₅CHClC₆H₅ gets hydrolysed more easily than C₆H₅CHCl.

This can be explained by considering S_NI reaction mechanism. In case of S_NI reactions reactivity depends upon the stability of carbo cations.
C₆H₅CHClC₆H₅ forms more stable carbo cation than C₆H₅CH₂Cl.

Question 8.
Treatment of alkyl halides with aq.KOH leads to the formation of alcohols, while in presence of alc.KOH what products are formed ?
Answer:

• Treatment of alkyl halides with aq. KOH leads to the formation of alcohols. Here Nucleo- phillic substitution reaction takes place.
  Eg.: C₂H₅Cl + aq.KOH → C₂H₅OH + KCl
• Treatment of alkyl halides with alc.KOH leads to the formation of alkenes. Here elimination reaction takes place.
  E.g.: C₂H₅Cl + alc. KOH → C₂H₄ + KCl + H₂O

Question 9.
What is the stereochemical result of S_N¹ and S_N² reactions ? [T.S. Mar. 17]
Answer:

• The stereochemical result of S_N¹ reaction is reacemisation product.
• The stereochemical result of _N² reaction is inversion product.

Question 10.
What type of isomerism is exhibited by O, m and p-chlorobenzenes ?
Answer:
o, m and p-chloro benzenes exhibits position isomerism.

These are positional isomers.

Question 11.
What are Enantiomers? [T.S. Mar. 19]
Answer:
Enantiomers : The stereo isomers relatëd to each other as non-superimposable mirror images are called enantiomers.

• These have identical physical properties like melting point, boiling points refractive index etc.
• They differ in rotation of plane polarised right.

Short Answer Questions

Questions 1.
Give the IUPAC names of the following compounds.
i) CH₃CH(Cl)CH(I)CH₃
ii) ClCH₂CH = CHCH₂Br
iii) (CCl₃)₃CCl
iv) CH₃C(p-Cl-C₆H₄)₂CH(Br)CH₃
Answer:

Question 2.
Write the structures of the following organic halides.
i) 1-Bromo-4-sec-butyl-2-methylbenzene,
ii) 2-Chioro- 1 -phenylbutane
iii) p-bromochlorobenzene l
iv) 4-t-butyl-3-iodoheptane.
Answer:
i) 1-Bromo-4-sec-butyl-2-methylbenzene.
Structure:

ii) 2-chloro- 1-phenylbutane.
Structure:

iii) p-bromo chlorobenzene Br
Structure:

iv) 4-t-butyl-3-iodoheptane
Structure:

Question 3.
A hydrocarbon C₅H₁₀ does not react with chlorine in dark but gives a single monochloro- compound C₅H₉Cl in bright sunlight. Identitfy the hydrocarbon.
Answer:

• The given compound molecular formula C₅H₁₀. It represents general formula C_nH_2n. It may be an alkene (or) cyclo alkane.
• Given that the alkene does not react with Cl₂ in dark condition it is not an alkene, so it is a cyclo alkene.
  

Question 4.
Which compound in each of the following pairs will react faster in. S_N² reaction with -OH ? [A.P. Mar. 19]
i) CH₃Br or CH₃I
ii) (CH₃)₃CO or CH₃Cl .
Answer:

1. Among CH₃Br and CH₃I, CH₃ – I reacts faster in S_N² reaction with OH^⊗ because bond dissociation energy of C – I is less than the bond dissociation energy of C – Br.
2. Among CH₃Cl and (CH₃)₃CCl, CH₃ – Cl reacts faster in S_N² reaction with OH^⊗ because (CH₃)₃CCl has high steric hindrance than CH₃Cl.

Question 5.
Predict the alkenes that would be formed in the following reactions and identify the major alkene.

Answer:

Question 6.
How will you carry out the following conversions ?
i) Ethane to bromomethene
ii) Toluene to benzyl alcohol
Answer:
i) Conversion of Ethane to Bromo Ethane.

ii) Conversion of toluene to benzyl alcohol:

Question 7.
Explain why the dipole moment of chlorobenzene Is lower than that of cyclohexyichloride.
Answer:
The dipole moment of chloro benzene is lower than that of cylo hexyl chloride.
Explanation:

• The polarity of C – Cl bond in chiorobenzene is less than the polarity of C — Cl bond in cyclo hexyl chloride.
• The above fact is due to the sp² hybridisation of ‘C’ atom in chiorobenzene where as in cyclo hexyl chloride ‘C’ atoms hybridisation is sp³ – hybridisation.
  

Question 8.
Write the mechanism of the following reaction.

Answer:
Given reaction is

CN^⊖ ion is an ambident nucleophile. It has the tendency to attack through C-atom (or) through N-atom. Attack through C-atom results cyanide product and attack through N- atom results isocyanide. But in presence of polar solvent KCN ionises and forms cyanide as major product.

Long Answer Questions

Question 1.
Name the following halides according to IUPAC system and classify them as primary, secondary, tertiary, vinyl or aryl halides,
i) CH₃CH(CH₃)CH(Br)CH₃
ii) CH₃C(Cl)(C₃H₅)CH₂CH₃
iii) m-ClCH₂C₆H₄CH₂C(CH₃)₃
iv) O-Br-C₆H₄CH(CH₃)CH₂CH₃
Answer:

Question 2.
Write the structures of the following organic halogen compounds.
i) 2-Bromo-3-methylhexane
ii) 2-(2-chlorophenyl)-1-iodooctane
iii) 4-tertiary-butyl-3-iodo benzene
iv) 1-Bromo-4-sec-butyl-2-methylbenzene.
Ans:
i) 2-Bromo-3-methyl hexane
Structure:

ii) 2-(2-chloro phenyl) 1-iodo octane
Structure:

iii) 4-tertiary-butyl-3-iodo benzene
Structure:

iv) 1 -Bromo-4-sec-butyl-2 -methyl benzene
Structure:

Question 3.
Discuss the physical properties of haloalkanes.
Answer:
Physical properties of halo alkanes:

1. Pure alkyl halides are colourless, Bromides and iodides exhibits colour when exposed to light.
2. Most of volatile halogen compounds have sweet smell.
3. Lower members of alkyl halides are gases and higher members are liquids (or) solids.
4. The boiling points of chlorides, bromides and iodides are higher than those of hydrocarbons.
5. The boiling points of alkyl halides decrease as follows RI > RBr > RCl > RF.
6. In case of isomeric halo alkanes boiling points decrease with increase in branching.
7. The density of halo alkane, increase with increase in no. of carbon atoms, halogen atoms and atomic mass of the halogen atoms.
8. Halo alkanes, have theTendency to dissolve in organic solvents and are very slightly soluble in water.

Question 4.
Explain the mechanism of Nucleophilic bimolecular substitution (S_N2) reaction with one example. [T.S. Mar. 16] [Mar. 14]
Answer:
Nucleophilic Bimolecular substitution Reaction S_N2:

1. The nucleophilic substitution reaction in which rate depends upon concentration of both reactants is called S_N2 reaction.
2. It follows 2^nd order kinetics. So it is called bimolecular reaction.
   Eg.: Methyl chloride reacts with hydroxide ion and forms methanol and chloride ion.
3. Here the rate of reaction depends upon the concentration of two reactants.
   
4. In the above mechanism the configuration of carbon atom under attack inverts in much the same way as an umbrella is turned inside out when caught in a strong wind. This process is called inversion of configuration.
5. In transition state the carbon atom is simultaneously bonded to the incoming nucleophile and out going group. It is very unstable.
6. The order of reactivity for S_N2 reactions follows : 1°-alkyl halides > 2°-alkyl halides > 3°-alkyl halides.

Question 5.
Explain why allylic and benzylic halides are more reactive towards S_N1 substitution while 1-halo and 2-halobutanes preferentially undergoes S_N2 substitution.
Answer:
1) Allylic and benzylic halides show high reactivity towards the S_N1 reaction.
Reason: The carbocation thus formed gets stabilised through resonance phenomenon as shown below.

2) 1-halo and 2-halo butanes preferentially under goes S_N2 substitute.
Reason : S_N2 reactions involve transition state formation. Higher the steric hindrance lesser the stability of transition state. The given 1-halo and 2-halo butanes have less steric hindrance so these are preferentially undergo S_N2 reaction.

Question 6.
Describe the stereo chemical effect on the hydrolysis of 2-bromobutane.
Answer:
When S-2-Bromobutane is allowed to undergo hydrolysis R-2-butanol is formed with the – OH group occupying the position opposite to what bromide had occupied. This is an example of S_N2 – reaction. S_N2 reactions of optically active halides are accompanied by inversion of configuration.

Question 7.
What is the criteria for optical activity. Give two examples of chiral molecules.
Answer:
Optical activity: The property of rotating the plane polarized light by a chemical substance is called optical activity.

• If the plane polarised light rotates in clock wise direction then it is dextro rotatory [(+) (or) d-forms].
• If the plane polarised light rotates in anti-clock wise direction then it is laevo rotatory [(-) or /-form].

Crieteria for optical activity:

1. Chirality (or) dissymmetry is the necessary and sufficient condition for a molecule to show optical activity.
   Chirality : The objects which are non-superimposable on their mirror images are said to be chiral and this property is known as chirality.
2. Asymmetry (absence of symmetry) of the molecule is responsible for the optical activity of organic compounds.
   Examples of chiral molecules :
   1. 2-Butanol
   2. 2-Chlorobutane
   3. 2-Bromopropanoic acid.

Question 8.
Define the following:    [A.P. Mar. 16]
i) Racemic mixture
ii) Retention of configuration
iii) Enantiomers.
Answer:
i) Racemic mixture: Equal portions of Enantiomers combined to form an optically inactive mixture. This mixture is called racemic mixture.

1. Here rotation due to one isomer will be exactly cancelled by the rotation of due to other isomer.
2. The process of conversion of enantiomer into a racemic mixture is called as racemisation.
   

ii) Retention of configuration: The preservation of the integrity of the spatial arrangement of bonds to an asymmetric centre during a chemical reaction (or) transformation is called Retention of configuration.
General Eg : Conversion of XC_abc chemical species into YC_abc.

Eg : (-) 2 – Methyl 1 – butanol conversion into (+) 1 – chloro 2. Methyl butane

iii) Enantiomers : The stereo isomers related to each other as non-superimposable mirror images are called enantiomers.

• These have identical physical properties like melting point, boiling points refractive index etc.
• They differ in rotation of plane polarised light.

Question 9.
Write the mechanism of dehydrohalogenation of 2-bromobutane.
Answer:
Dehydrohalogenation of 2 – Bromobutane: 2 – Bromobutane reacts with alc.KOH to form 2 – Butene as major product.

Mechanism:

• 2 – Bromobutane heated with alc.KOH elemination of hydrogen atom from β – carbon and bromine atom from α – carbon takes place. This is called β – Elimination.
  
• 2 – Butene is major product formed according to saytzev’s rule. “In dehydrohalogenation reactions the preferred product is that alkene which has the greater no. of alkyl groups attached to double bonded carbon atoms”.

Question 10.
Explain the Grignard reagents preparation and application with suitable example.
Answer:
Alkyl magnesium halides are generally called as Grignard reagenty.
Preparation: These are prepared by the treatment of alkyl halides with magnesium metal in presence of dry ether.

Applications:
Grignard reagents have wide applications in the synthesis of large no. of organic compounds.

1. Preparation of alkanes :
   Grignard reagents reacts with alcohols and forces alkanes.
   
2. Preparation of alcohols : Ethylalcohol is obtained by the action of Methyl magnesium bromide on formal dehyde followed by the hydrolysis.
   
3. Preparation of carboxylicacids:
   Grignard reagent on carboxylation followed by the hydrolysis to form carboxylic acids.
   

Question 11.
A primary alkyl halide C₄H₉Br(A) reacted with alcoholic KOH to give compound B. B on reaction with HBr yields C which is an isomer of A. When A is reacted with sodium metal forms D, C₈H₈ which is different from the compound formed when n-butylbromide is reacted with sodium. Give the structural formulae of A-D and write equations for all the reactions.
Answer:
Given 1° – alkyl halide molecular formula C₄H₉Br
Two isomers possible with molecular formula C₄H₉Br (i- alkyl halides)

Given that compound ‘A’ when reacted with Na does not forms the same product produced by n — Butyl bromide.
∴ isomer I cannot be ‘A’.

Question 12.
Account for the following statements:
i) Aryihalides are extremely less reactive towards Nucleophilic substitution reactions.
ii) p-Nitrochlorobenzene and o, p-dinitrochlorobenzene undergo Nucleophilic substitution readily compared to chlorobenzene.
Answer:
i) Aryl halides are extremely less reactive towards nucleophilic substitution reactions due to following reasons.

• In aryl halides ‘C’ undergoes SP² hybridised and it has greater S – character ånd electro negativity So the C – X bond length is shorter.
• In aryl halides resonance effect plays an important role.
  The electron pairs on halogen atom are in conjugation with it π – electrons of the ring.
  
  In the above C – Br bond acquires apartial double bond nature due to resonance. This bond cleavage is difficult.
• The phenyl cation formed in aryl halides is not stabilised by resonance.

ii) p – nitrochlorobenzene and o, p – dinitro chlorobenzene undergo nucleophillic substitution reachily compared to chlorobenzene due to the following reasons.

• Due to presence of – NO₂ group which is an electron with drawing group at ’O’ and ‘P’ – positions in the ring makes the bond breaking easy.
• As the number of NO₂ groups increases reactivity of aryl halide also increases. This can be evidended by the following reactions.
  
  

Question 13.
Explain how the following conversions are carried out:
i) Propene to Propanol
ii) Ethanol to but-1-yne
iii) 1-Bromopropane to 2-Bromopropane
iv) Aniline to Chlorobenzene.
Answer:
i) Propene to propanol

iv) Aniline to chlorobenzene

Question 14.
What happens when
i) n-butylchloride is treated with alc.KOH.
ii) Bromobenzene is treated with Mg in presence of dry ether.
iii)Methylbromide is treated with sodium in presence of dry ether.
Answer:
i) n-Butylchloride + treated with alc.KOH undergo dehydro halogenation and forms 1-Butene.
CH₃ – CH₂ – CH₂ – CH₂ – Cl + alc. KOH → CH₃ – CH₂ – CH = CH₂ + kCl + H₂O

ii) Bromobenzene is treated with Mg in presence of dry ether forms phenyl magnesium bromide a Grignard reagent.

iii) Methyibromide is treated with sodium in presence of dry ether forms ethane (wurtz reaction)

Question 15.
Write the reactions showing the major and minor products when chlorobenzene is reacted with CH₃Cl and CH₃COCl in presence of AlCl₃.
Answer:
i) Friedel crafts alkylation : When chiorobenzene is treated with CH₃Cl to form 1 – Chloro – 4 – Methyl benzene (major) and 1 – Chloro 2 – Methylbenzene (minor).

ii) Friedel Craft’s acylation: Chlorobenzene reacts with CH₃COCl in presence of Anhydrous AlCl₃ to form 2 – Chloro actophenone, (Minor) and 4 – Chloro acetophenone (major).

Textual Examples

Question 1.
Draw the structures of all the eight structural isomers that have the molecular formula C₅H₁₁Br. Name each isomer according to IUPAC system and classify them as primary, secondary or tertiary bromide.
Solution:
CH₃CH₂CH₂CH₂CH₂Br      1-Bromopentane (1°)
CH₃CH₂CH₂CH(Br)CH₃      2-Bromopentane (2°)
CH₃CH₂CH(Br)CH₂CH₃       3-Bromopentane (2°)
(CH₃)₂CHCH₂CH₂Br            1-Bromo-3-methylbutane (1°)
(CH₃)₂CHCHBrCH₃              2-Bromo-3-methylbutane (2°)
(CH₃)₂CBrCH₂CH₃               2-Bromo-2-methylbutane (3°)
CH₃CH₂CH (CH₃) CH₂Br     1-Bromo-2-methylbutane (1°)
(CH₃)₃CCH₂Br                      1-Bromo-2, 2-dimethyipropane (1°)

Question 2.
Write IUPAC names of the following:

Solution:

1. 4-Bromopent-2-ene
2. 3-Bromo-2-methylbut-l-ene
3. 4-Bromo-3-methylpent-2-ene
4. 1-Bromo-2-methylbut-2-ene
5. 1-Bromobut-2-ene
6. 3-Bromo-2-methylpropene

Question 3.
Identify all the possible monochloro structural isomers expected to be formed on free radical monochlorination of (CH₃)₂CHCH₂CH₃.
Solution:
In the given molecule, there are four different types of hydrogen atoms. Replacement of these hydrogen atoms will give the following.
(CH₃)₂CHCH₂CH₂Cl
(CH₃)₂CHCH(Cl)CH₃
(CH₃)₂C(Cl)CH₂CH₃
CH₃CH(CH₂Cl)CH₂CH₃

Question 4.
Write the products of the following reactions

Solution:

Question 5.
Haloakanes react with KCN to form alkyl cyanides as main product while AgCN forms isocyanides as the chief product. Explain.
Solution:
KCN is predominantly ionic and provides cyanide ions in solution. Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack takes place mainly through carbon atom and not through nitrogen atom since C-C bond is more stable than C-N bond. However, AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanide as the main product.

Question 6.
In the following of halogen compounds, which would undergo S_N2 reaction faster ?

Solution:
It is primary halide and therefore undergoes S_N2 reaction faster.
As iodine is a better leaving group because of its large size, it will be released at a faster rate in the presence of incoming nucleophile.

Question 7.
Predict the order of reactivity of the following compounds in S_N1 and S_N2 reactions.
i) The four isomeric bromobutanes
ii) C₆H₅CH₂Br, C₆H₅CH(C₆H₅)Br, C₆H₅CH(CH₃)Br, C₆H₅C(CH₃)(C₆H₅)Br
Solution:
i) CH₃CH₂CH₂CH₂Br < (CH₃)₂CHCH₂Br < CH₃CH₂CH(Br)CH₃ < (CH₃)₃CBr (S_N1)
CH₃CH₂CH₂CH₂Br > (CH₃)₂CHCH₂Br > CH₃CH₂CH(Br)CH₃ > (CH₃)₃CBr (S_N2)
Of the two primary bromides, the carbocation intermediate derived from (CH₃)₂CHCH₂Br is more stable than that derived from CH₃CH₂CH₂CH₂Br because of greater electron donating inductive effect of (CH₃)₂CH-group. Therefore, (CH₃)₂CHCH₂Br is more reactive than CH₃CH₂CH₂Br in S_N1 reactions. CH₃CH₂CH(Br)CH₃ is a secondary bromide and (CH₃)₃ CBr is a tertiary bromide. Hence the above order is followed in S_N1. The reactivity in S_N2 reactions follows the reverse order as the steric hinderance around the electrophilic carbon increases in that order.

ii) C₆H₅C(CH₃)(C₆H₅) Br > C₆H₅CH(C₆H₅)Br > C₆H₅CH(CH₃)Br > C₆H₅CH₂Br (S_N1)
C₆H₅C(CH₃) (C₆H₅) Br < C₆H₅CH(C₆H₅)Br < C₆H₅CH(CH₃)Br < C₆H₅CH₂Br (S_N2)
Of the two secondary bromides, the carbocation intermediate obtained from C₆H₅CH(C₆H₅)Br is more stable than obtained from C₆H₅CH(CH₃)Br because it is stabilised by two phenyl groups due to resonance. Therefore, the former bromide is more reactive than the latter in S_N1 reactions. A phenyl group is bulkier than a methyl group. Therefore, C₆H₅CH(C₆H₅)Br is less reactive than C₆H₅CH(CH₃)Br in S_N2 reactions.

Question 8.
Identify chiral molecules in each of the following pair of compounds. (Wedge and Dash representations according to Inter 1 yr., fig. 13.1).

Solution:

Question 9.
Although chlorine is an electron withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions. Why ?
Solution:
Chlorine withdraws electrons through inductive effect and releases electrons through resonance. Through inductive effect, chlorine destabilises the intermediate carbocation formed during the electrophilic substitution.

Through resonance, halogen tends to stabilise the carbocation and the effect is more pronounced at ortho-and para-positions. The inductive effect is stronger than resonance and causes net electron withdrawl and thus causes net deactivation. The resonance effect tends to oppose the inductive effect for the attack at ortho-and para-positions and hence makes the deactivation less for ortho-and para-attack. Reactivity is thus controlled by the stronger inductive effect and orientation is controlled by resonance effect.

Intext Questions

Question 1.
Write structures of the following compounds:
i) 2-Chloro-3-methylpentane
ii) 1-Chloro-4-ethylcyclohexane
iii) 4-tert. Butyl-3-iodoheptane
iv) 1, 4-Dibromobut-2-ene
v) 1-Bromo-4-sec. butyl-2-methylbenzene.
Answer:

Question 2.
Why is sulphuric acid not used during the reaction of alcohols with KI ?
Answer:
H₂SO₄ cannot be used along with KI in the conversion of an alcohol to an alkyl iodide as it converts KI to corresponding acid, HI which is then oxidised by it to I₂.

Question 3.
Write structures of different dihalogen derivatives of propane.
Answer:

1. ClCH₂CH₂CH₂Cl
2. ClCH₂ CHClCH₃
3. Cl₂CHCH₂ CH₃
4. CH₃CCl₂ CH₃

Question 4.
Among the isomeric alkanes of molecular formula C₅H₁₂, identify the one that on photo¬chemical chlorination yields.
i) A single monochloride,
ii) Three isomeric monochlorides,
iii) Four isomeric monochlorides.
Answer:
i)

All the hydrogen atoms are equivalent and replacement of any hydrogen will give the same product.

ii) C^aH₃C^bH₂C^cH₂C^bH₂C^aH₃
The equivalent hydrogens are grouped as a, b and c. The replacement of equivalent hydrogens will give the same product.

iii)

Similarly the equivalent hydrogens are grouped as a, b, c and d. Thus, four isomeric products are possible.

Question 5.
Draw the structures of major monohalo products in each of the following reactions.

Answer:

Question 6.
Arrange each set of compounds in order of increasing boiling points.

1. Bromomethane, Bromoform, Chloromethane, Dibromomethane.
2. 1 – Chloropropane, Isopropyl chloride, 1 – Chlorobutane.

Answer:

1. Chloromethane, Bromomethane, Dibromomethane, Bromoform. Boiling point increases with increase in molecular mass.
2. Isoporpylchloride, 1 – Chloropropane, 1 – Chlorobutane. Isopropylchloride being branched has lower b.p. than 1 – Chloropropane.

Question 7.
Which alkyl halide from the following pairs would you expect to react more rapidly by an S_N2 mechanism ? Explain your answer.

Answer:
i) CH₃CH₂CH₂CH₂Br Being primary halide, there won’t be any steric hindrance.

ii)

Secondary halide reacts faster than tertiary halide.

iii)

The presence of methyl group closer to the halide group will increase the steric hindrance and decrease the rate.

Question 8.
In the following pairs of halogen compounds, which compound undergoes faster S_N1 reaction?

Answer:
i) Tertiary halide reacts faster than secondary halide because of the greater stability of tert-carbocation.

ii) Because of greater stability of secondary carbocation than primary.

Question 9.
Identify A, B, C, D, E, R and R¹ in the following:

Answer:

Andhra Pradesh BIEAP AP Inter 2nd Year Chemistry Study Material 9th Lesson Biomolecules Textbook Questions and Answers.

AP Inter 2nd Year Chemistry Study Material 9th Lesson Biomolecules

Very Short Answer Questions

Question 1.
Define Carbohydrates.
Answer:
The compounds which are primarily produced by plants and form a very large group of naturally occuring organic compounds are called Carbohydrates.
Eg: Glucose, Fructose, Starch.
-H> Carbohydrates are the polyhydroxy aldehydes (or) ketones.

Question 2.
Name the different types of carbohydrates on the basis of their hydrolysis. Give one example for each.
Answer:
On the basis of the hydrolysis, carbohydrates are classified as

1. Monosaccharides, Eg : Glucose, fructose No saccharides
2. Oligosaccharides, Eg : Sucrose, maltose two monosaccharides
3. Polysaccharides, Eg : Starch, cellulose large number of monosaccharides.

Question 3.
Why are sugars classified as reducing and non-reducing sugars ?
Answer:
Carbohydrates that reduce Fehling’s reagent, Tollen’s reagent are called reducing sugars.
Eg: Glucose.
Carbohydrates that doesnot reduce Fehling’s reagent, Tollen’s reagent are called non reducing sugars.
Eg : Sucrose.

Question 4.
What do you understand from the names
(a) aldo pentose and
(b) ketoheptose ?
Answer:
a) Aldo pentose : If a monosaccharide contains 5 carbon atoms with aldehyde group then it is known as aldo pentose.
b) Ketoheptose : If a monosaccharide contain seven carbons with a ketone group then it is called ketoheptose.

Question 5.
Write two methods of preparation of glucose.
Answer:
Methods of preparations of glucose :
1) From Sucrose.: Sucrose when boiled with di/.HC/ in alcoholic solution then glucose, fructose are obtained in equal portions.

2) From Starch : Starch undergo hydrolysis, with dil. H2S04 at 393K under pressure to form glucose.

Question 6.
Glucose reacts with bromine water to give gluconic acid. What information do you get from this reaction about the structure of glucose ?
Answer:
Glucose reacts with bromine water to give gluconic acid. This reaction indicates that the carbonyl group present ip,glucose is an aldehyde group.

Question 7.
Glucose and gluconic acid on oxidation with nitric acid give saccharic acid. What Information do you get from this reaction about the structure of glucose ?
Answer:
Glucose and gluconic acid on oxidation with nitric acid give saccharic acid. This indicates the presence of primary alcoholic (-OH) group in glucose.

Question 8.
Glucose reacts with acetic anhydride to form penta acetate. What do you understand about the structure of glucose from this reaction ?
Answer:
Glucose reacts with acetic anhydride to form peta acetate. It confirms the presence of five- OH groups in glucose which are attached to different carbon atoms.

Question 9.
Give any two reasons to understand that glucose molecule has no open chain structure.
Answer:
Open chain structure of glucose could not explain

• why glucose doesnot respond to Schiffs test,
• why it does not react with NaHSO₃ and NH₃,
• why there is mutarotation.

Question 10.
D – glucose means dextro rotatory glucose. Is it true ? Why ?
Answer:
In glucose the carbon atom attached to the lowest CH₂-OH group is found to contain H atom on left side. So it is correlated to glyceraldehyde molecule and gives D-symbol. D-Glucose means not dextro rotatory glucose. D-symbol has nothing to do with optical activity of compound.

Question 11.
What are anomers ?
Answer:
Anomers : The two isomeric structures of a compound which differ in configuration at C-l only are called Anomers.

Question 12.
Write the ring structure of D-glucose. What are their names?
Answer:

Question 13.
Write the ring structure and open chain structure of fructose.
Answer:

Question 14.
What do you understand by invert sugars?
Answer:
During the hydrolysis of sucrose there is a change in the sign of rotation, from dextro (+) to laevo (-) and the product is named as invert sugar.

Question 15.
What are amino acids? Give two examples.
Answer:
The organic compounds which contain amino (-NH₂) functional group and carboxyl (-COOH) functional group are called amino acids.
Eg: Glycine, Alanine etc.

Question 16.
Write the structure of alanine and aspartic acid.
Answer:

Question 17.
What do you mean by essential amino acids ? Give two examples for non essential amino acids? [T.S. Mar. 16]
Answer:
Essential amino acids : The amino acids which cannot be synthesized in the body and must be obtained through diet are known as essential aminoacids.
Eg : valine,. leucine etc.
Examples of non essential amino acids are Alanine, glycine, Aspartic acid.

Question 18.
What is zwitter ion ? Give an example.
Answer:
Zwitter ion : In aqueous solution of amino acids, the carboxyl group can lose a proton and amino acid can accept that proton to form a dipolar ion. This ion is called as zwitter ion.

Question 19.
What are proteins ? Give an example.
Answer:
Proteins : A poly peptide with more than hundred amino acid residues, having molecular mass higher than 10,000 units is called a protein.
Eg : keratin, myosin, insulin.

Question 20.
What are fibrous proteins ? Give examples.
Answer:
When the poly peptide chains run parallel and are held together by hydrogen and disulphide bonds then fibre – like structure is formed. These are called fibrous proteins. These are insoluble in water.
Eg : keratin, myosin.

Question 21.
What are globular proteins ? Give examples.
Answer:
When the chains of polypeptides coil around to give a spherical shape then globular proteins are formed. These are usually soluble in water.
Eg : insulin and albumins.

Question 22.
How are proteins classified with respect to peptide bond ?
Answer:
With respect to peptide bond proteins classified into two types.

1. Fibrous proteins
2. Globular proteins.

Question 23.
What are the components of a nucleic acid ?
Answer:

• Nucleic acids are long chain polymers of nucleotides i.e poly nucleotides,
• Nucleic acids are constituted by pentose sugar, phosphoric acid, and nitrogenous hetero cyclic base (purine (or) pyrimidine).

Question 24.
Write the names of three types of RNA.
Answer:
Three types of RNA are :

1. Messenger RNA (m – RNA)
2. Ribosomal RNA (r – RNA)
3. Transfer RNA (t – RNA).

Question 25.
Write the biological functions of nucleic acids.
Answer:
Biological functions of Nucleic acids :

• DNA is the chemical basis of heredity.
• DNA is the reserve of genetic information.
• DNA is capable of self duplication during cell division and identical DNA strands are transfered to daughter cells.
• RNA molecules are used in the protein synthesis in the cell
• The message for the synthesis of a protien is present in DNA.

Question 26.
Name the vitamin responsible for the coagulation of blood.
Answer:
The vitamin responsible for the coagulation of blood is vitamin K.

Question 27.
What are monosaccharides ?
Answer:
A carbohydrate which donot form any saccharide unit on hydrolysis (or) which cannot be hydrolysed is called monosaccharide.
Eg : glucose, fructose.

Question 28.
What are reducing sugars ?
Answer:
Carbohydrates that reduce Fehling’s reagent, Tollen’s reagent are called reducing sugars.
Eg : glucose.

Question 29.
Write two main functions of carbohydrates in plants.
Answer:
Carbohydrates are essential for life of plants.

• Carbohydrates are used as storage molecules as starch in plants.
• Cell wall of plants is made up of cellulose.

Question 30.
Classify the following into monosaccharides and disaccharides,

1. ribose
2. 2-deoxy ribose
3. maltose
4. fructose.

Answer:

1. Ribose – Monosaccharide
2. 2 – deoxy ribose – Monosaccharide
3. Maltose – Disacch&ride .
4. Fructose – Monosaccharide.

Question 31.
What do you understand by the term glycosidic linkage ?
Answer:
The linkage between two monosacharides of disacharides is called glycosidic linkage.

Question 32.
What is glycogen ? How is it different from starch ?
Answer:
The carbohydrate which is stored in animal body is called glycogen. It is also known as animal starch. Starch is a polysaccharide which is stored in plants where as glycogen is stored in animals (liver, muscles and brain).

• Glycogen mainly resembles amylopectin of starch in structure but glycogen is more branched than amylopectin.

Question 33.
What are the hydrolysis products of
i) sucrose and
ii) lactose ?
Answer:
i) The hydrolysis products of sucrose are glucose and fructose.

ii) The hydrolysis products of lactose are galactose and glucose.

Question 34.
What is the basic structural difference between starch and cellulose ?
Answer:
In cellulose a straight chain polysaccharide composed only of β – D – glucose units which are joined by glycosidic linkage between C – 1 of one glucose unit and C – 4 of the next glucose unit.

Starch consists of two components – Amylose and Amylopectin. Amylose is a long un branched chain with 200 – 1000 α – D – glucose units held by C – 1 to C – 4 glycosidic linkage. Amylopectin is a branched chain polymer of α – D – glucose units in which Chain is formed by C – 1 to C – 4 glycosidic linkage where as branching occurs by C – 1 to C – 6 glycosidic linkage.

Question 35.
What happens when D – glucose is treated with the following reagents :
i) HI
ii) Bromine water
iii) HNOs.
Answer:
i) D – glucose on prolonged heating with HI, glucose forms n – hexane.

Question 36.
Enumerate the reactions of D – glucose which cannot be explained by its open chain structure.
Answer:
The following reactions cannot be explained by the open chain structure of D – glucose.

• Glucose has aldehyde group, but it does not respond to the reagents like Schiff s reagent, NaHSO₃, NH₃ etc., .
• The penta acetyl derivative of glucose doesnot react with hydroxyl amine.
• α and β – methyl glucosides cannot be explained by its open chain structure.

Question 37.
What are essential and non – essential amino acids ? Give one example for each.
Answer:
Essential amino acids : The amino acids that cannot be synthesised by the body and must be supplied in the diet are called essential amino acids.
Eg : valine, leucine, phenyl alanine etc.,

Non-essential amino acids : Other amino acids synthesised by the tissues of the body are called non-essential amino acids.
Eg : Glycine, alanine etc.,

Question 38.
Define the following as related to proteins :
i) Peptide linkage
ii) Primary structure
iii) Denaturation
Answer:
i) Peptide linkage :
Amide linkages between amino acids are known as peptide linkages. The product obtained from two amino acid molecules through peptide bond is called a dipeptide. Peptide chain may be extended to many amino acids.

Proteins are naturally occuring polypeptides that contain more than 50 amino acid units.

ii) Primary structure : The primary structure of protein is defined as the linear sequence of amino acid residues making up its polypeptide chain. Proteins may be formed of one or more polypeptide chains. The amino acid residues are linked by peptide bonds. The peptide bond is formed between carboxyl group of one amino acid and amino group of adjacent amino acid.
Eg : fibroin of silk.

iii) Protein Denaturation : The phenomenon of disorganization of native protein structure is known as denaturation. Denaturation results in the loss of secondary, tertiary nad quaternary structure of proteins. This involves a change in physical, chemical and biological properties of protein molecules.
Agents of denaturation:
Physical agents – Heat, violent shaking, X – rays, UV – radiation
Chemical agents – Acids, alkalies, organic solvents, urea, salts of heavy metals.

Question 39.
What are the common types of secondary structure of proteins ?
Answer:
Secondary structure: The secondary structure explains the shape of the polypeptide chain. It is derived from the primary structure by the formation of hydrogen bond interactions between amino acid residues.

Disulfide bonds also occur either in same chain or between polypeptide chains. The secondary structure is classified into two types namely helical structure and pleated sheets, e.g.: Keratin of hair.

Question 40.
What type of bonding helps in stabilizing the α – helix structure of proteins ?
Answer:
The α – helix structure of proteins is stabilized by intramolecular hydrogen bonding between = O and – H groups of dlifferent peptide bonds.

Question 41.
Differentiate between globular and fibrous proteins.
Answer:
Globular proteins

• In this proteins the chains of poly peptides coil around to give a spherical shape
• These are soluble in water
• Eg: Insulin

Fibrous proteins

• In this proteins the poly peptides run parallel and are held together by hydrogens and disulphite – bondy
• These are insoluble in water
• Eg: keratin

Question 42.
How do you explain the amphoteric behaviour of amino acids ?
Answer:
Amino acids are the compounds having amino group (-NH₂) i.e., a basic group and carboxyl group (-COOH) i.e., an acidic group

Zwitter ion,: In aqueous solution of amino acids, the carboxyl group can lose a proton and amino acid can accept that proton to form a dipolar ion. This is called as zwitter ion.

In zwitter ion form amino acids behave both acidic as well as basic nature. Therefore amino acids are amphoteric in nature.

Question 43.
Why are vitamin A and vitamin C essential to us ? Give their important sources.
Answer:
vitamin A and vitamin C are essential to us.
Explanation :

• Deficiency of vitamin A causes night blindness, red ness in eyes, xerophthalhia
• Deficiency of vitamin C causes pernicious anaemia (RBC deficient in haemoglobin)

Sources :

• Vitamin – A : Fish liver oil, carrots, butter and milk.
• Vitamin – C : Citrous fruits, amla, green leafy vegetables.

Question 44.
What are nucleic acids ? Mention their two important functions.
Answer:

• Nucleic acids are long chain polymers of nucleotides i.e poly nucleotides.
• Nucleic acids are constituted by pentose sugar, phosphoric acid, and nitrogenous hetero cyclic base (purine (or) pyrimidine).

Biological functions of Nucleic acids :

• DNA is the chemical basis of heredity.
• DNA is the reserve of genetic information.
• DNA is capable of self duplication during cell division and identical DNA strands are transfered to daughter cells.
• RNA molecules are used in the protein synthesis in the,cell.
• The message for the synthesis of a protien is present in DNA.

Question 45.
What is the difference between a nucleoside and a nucleotide ?
Answer:
Nucleosides: Nucleic acid bases combine with pentose sugars to form N – glycosides known as nucleosides.
Eg: Cytidine
Structure of Cytidine

Nucleotides : Nucleotide is a phosphate ester of nucleoside and consists of a purine or pyrimidine base. Nucleotide contains a base moiety, a sugar moiety (i.e.,) a nucleoside moiety and phosphate group.
Nucleotide = base (purine / pyrimidine) + sugar (ribose/deoxyribose) + phosphate
Ex: Adenosine Triphosphate (ATP)

Short Answer Questions

Question 1.
How are the carbohydrates classified on the basis of their
a) Taste
b) Hydrolysis
c) Functional groups
Answer:
a) Taste : On the basis of their taste carbohydrates are classified into
i) Sugars, ii) Non sugars.

1. Sugars : Carbohydrates which are sweet in taste.
   Eg : Sucrose.
2. Non sugars : Carbohydrates which are not sweet in taste.
   Eg : Cellulose.

b) Hydrolysis : On the basis of the hydrolysis, carbohydrates are classified as

1. Monosaccharides, Eg: Glucose, fructose No saccharides
2. Oligosaccharides. Eg: Sucrose, maltose two monosaccharides
3. Polysaccharides, Eg: Starch, cellulose large number of monosacchandes.

c) Functional groups: Carbohydrates classified into two types on the basis of functional group present.

1. Aldoses: Carbohydrates having aldehyde group.
   Eg: glucose.
2. Ketoses: Carbohydrates having ketone group.
   Eg: fructose.

Question 2.
Write a brief note on the structure of glucose.
Answer:
1. The molecular formula of glucose is found to be C₆H₁₂O₆. It can be written as CHO – (CHOH)₄ – CH₆OH’.

2. Acylation of glucose with acetic anhydride gives glucose pentacetate. Hence glucose molecule has five -OH groups.

3. Glucose reacts with hydroxylamine and hydrogen cyanide forming corresponding oxime and cyano hydrin respectively. Hence glucose molecule has carbonyl group.

4. Glucose on oxidation with Tollens reagent and Fehling’s solution gives gluconic acid. Hence carbonyl group present in glucose is aldehydic group.

5. Glucose on oxidation with nitric acid gives glucaric (saccharic) acid. This suggests that glucose molecule has primary alcoholic group (-CH₂OH).

6. On reduction with HI, glucose gives n – hexane.

7. Open chain structure of glucose:
Based on above observations, glucose is given the open chain structure.

8. Objections against open chain structure of glucose :
Open chain structure of glucose could not explain

1. Why glucose does not respond to schiffs test.
2. Why it does not react with NaH SO₃, and NH₃.
3. Why there is mutarotation.

Mutarotation :
Change in specific rotation of a compound from certain value to fixed value is known as “Mutarotation”.
The specific rotation of α – glucose is + 110° and that of β – form is + 19.7°. If each of them is separately dissolved in water and allowed to stand, their specific rotation gradually change and reach to a specific constant value + 52.5°.

9. Cyclic structure of glucose :

These two structures have difference in configuration at ‘C₁‘ only and are called ANOMERS.
Cyclic structure of glucose explains all the properties of glucose.

10. Pyranose structure of glucose :

Question 3.
Write short notes on sucrose.
Answer:
Sucrose is a disaccharide. It under go hydrolysis and forms equimolar mixture of D(+) glucose and D(-) fructose.
C₁₂ H₂₂ O₁₁ + H₁₂O → C₆ H₁₂ O₆ (glucose) + C₆ H₁₂ O₆ (fructose).

• In sucrose two monosaccharide units are held together by a glycosidic linkage between C – 1 of α – glucose and C – 2 of β – glucose.
• Sucrose is a non reducing sugar.
  
  During the hydrolysis of sucrose there is a change in the sign of rotation, from dextro (+) to laevo (-) and the product is named as invert sugar.

Question 4.
Write the structure of maltose and lactose. What are the products of hydrolysis of maltose and lactose?
Answer:
Structure of maltose:

• Maltose is formed from two α – glucose units (Disaccharide)
• C – 1 of one glucose linked to C -4 of another glucose
• It is a reducing sugar because C – 1 of 2^nd glucose is solution have free aldehyde group.
  
• maltose on hydrolysis to form two glucose units
  C₁₂ H₂₂ O₁₁ (Maltose) + H₂O → C₆H₁₂O₆ (glucose) + C₆H₁₂O₆ (glucose)

Structure of lactose:

• Lactose is milk sugar.
• Lactose is formed by the combination of β – glucose and β – galactose (Disaccharide)
• The linkage between C – 1 of galactose and c – 4 of glucose.
• It is a reducing sugar.
  
• Lactose on hydrolysis to form glucose and galactose
  C₁₂ H₂₂ O₁₁ (Lactose) + H₂O → C₆H₁₂O₆ (glucose) + C₆H₁₂O₆ (galactose)

Question 5.
Write about polysaccharides with starch and cellulose as examples.
Answer:
Polysaccharides : The saccharides which on hydrolysis to form large number of monosaccharides are called polysaccharides.
Eg : Starch and cellulose Starch :

• Starch is the most important dietary source for human beings.
• Vegetables, roots, cereals are important sources of starch.
• It is a polymer of α – glucose.
• It is constituted by two components Amylose and amylopectin.

Amylose :

• It constitutes 15 – 20% of starch.
• Amylose is water soluble component.
• Amylose is a branched chain with 200 – 1000 α – D – glucose units held by C – 1 to C -4 glycosidic linkage.

Amylopectin:

• Amylopectin constitutes 80 – 85% of starch.
• It is a branched chain polymer of a – glucose units in which chain is formed by C – 1 to C – 4 glycosidic linkage whereas branching occurs by C – 1 to C – 6 glycosidic linkage.

Cellulose :

• ellulose occurs in plants and it is the most abundant organic substance.
• It is a major constituent of cell wall of plant cells.
• Cellulose is a straight chain polysaccharide composed only of β – D – glucose units which are joined by glycosidic linkage between C – 1 of one glucose and C – 4 of the next glucose.

Question 6.
Write the importance of carbohydrates.
Answer:
Importance of carbohydrates :

• Carbohydrates are essential for life of plants.
• Carbohydrates are used as storage molecules as starch in plants.
• Cell wall of plants is made up of cellulose.
• Carbohydrates are also essential for life of animals. Carbohydrates are used as storage molecules as glycogen in animals.
• Carbohydrate source hohey is used for a long time as an instant source of energy.

Question 7.
Explain the classification of proteins as primary, secondary, tertiary and quartemary proteins with respect ot their structure.
Answer:
Protein structure’s and shapes are studied at four different levels as
i) Primary ii) Secondary iii) Tertiary iv) Quaternary structures

i) Primary structure : The primary structure of protein is defined as the linear sequence of amino acid residues making up its polypeptide chain. Proteins ‘may be formed of one or more polypeptide chains. The amino acid residues are linked by peptide bonds. The peptide bond is formed between carboxyl group of one amino acid and amino group of adjacent amino acid.
Eg : fibroin of silk.

R₁ – amino acid 1
R₂ – amino acid 2

ii) Secondary structure : The secondary structure explains the shape of the polypeptide chain. It is derived from the primary structure by the formation of hydrogen bond interactions between amino acid residues.

Disulfide bonds also occur either in same chain or between polypeptide chains. The secondary structure is classified into two types namely helical structure and pleated sheets.
Eg. : Keratin of hair

iii) Tertiary structure : Tertiary structure is exhibited by proteins having only one polypeptide chain. The three dimensional structure of a protein is referred to as tertiary structures. Fibrous and globular proteins are formed by tertiary structures. Various bonds are responsible for tertiary structure.

• Hydrophobic interactions
• Hydrogen bonds
• Disulphide bonds (- CH2 – S – S – CH2 -)
• Ionic or electrostatic interactions
• Vander Waal forces
  e.g : Myoglobin, Ribonuclease

iv) Quaternary structure : Two or more poly- peptide chains associate together to protect quaternary structure. A protein with a quaternary structure is referred to as an oligomes.
Eg. : Hemoglobin a chain

Question 8.
Explain the denaturation of proteins. [T.S. Mar. 16]
Answer:
The phenomenon of disorganization of native protein structure is known as denaturation. Denaturation results in the loss of secondary, tertiary and quaternary structure of proteins. This involves a change in physical, chemical and biological properties of protein molecules.
Agents of denaturation :
Physical Agents – Heat, violent shaking, X – rays, UV – radiation.
Chemical Agents – Acids, alkalies, organic solvents, urea, salts of heavy metals.

Question 9.
What are enzymes ? Give examples ?
Answer:
The group of complex proteinoid organic compounds, elaborated by living organism ‘which catalyse specific organic reactions are called enzymes.
Eg.: Lipases, Rennin, Maltase, Invertase etc. Practic ally all biological processes such as digestion, respiration etc., are carried on through the agency of enzymes.
Enzymes may be defined as biocatalysts synthesised by living cells.
The functional unit of enzyme is known as holo enzyme made up at apo enzyme (protein part) a co enzyme (non-protein part)

Question 10.
Explain the role of sucrose in its hydrolysis.
Answer:

• Sucrose is dextrorotatory but after hydrolysis gives dextrorotatory glucose and laevorotatory fructose.
• The laevorotation of fructose (-92.4°) is more than dextrorotation of glucose (+52.5°). This mixture is leavo rotators.
• During the hydrolysis of sucrose there is a change in the sign of rotation, from dextro (+) to laevo (-) and the product is named as invert sugar.

Question 11.
Write notes on vitamins.
Answer:
Vitamin is defined as an “accessory food factor which is essential for growth and healthy maintenance of the body.”
Classification : Vitamins are broadly classified into two major groups.
a) the fat soluble Eg : vitamin A, D, E and K.
b) water soluble Eg : vitamin B – complex and C.

Question 12.
What do you understand by “The two strands of DNA are complementary to each other” ? Explain.
Answer:
Structure of DNA : To understand the structure of DNA, we should know the charagaff s rule, which states that:

• Base composition on DNA for a particular organism is constant throughout all the somatic cells.
• Base composition always varies from one organism to another and is expressed by the dissymmetry ratio \(\frac{(A+T)}{(G+C)}\).
• Organisms closely related to each other often have similar base composition and hence – have closed values for their dissymmetry ratios.
• In a given organism the amount of adenine is always equal to the amount of thymine (A = T) and amount of guanine is equal to amount of cytosine (G = C).
• In a given organism the total amount of purine, bases
  are always equal to total number of pyrimidine bases (i.e.,) (A + G = T + C).
  M. Wilkins found that within the crystal there is a repeat distance of 3.4 nm and there are ten subunits per him.
  

Watson – Crick model for DNA : From the above observations Watson and Crick constructed a model for DNA. This model consists of two right handed polynucleotide chains that are complimentary and coiled about the same axis to form double-helix. Some specific base pairs can be spatially accommodated and these are A – T and G – C pairs. The bases are closely associated with each other by hydrogen bonding.

The helix has diameter of about 2.0 nm and contains 10 nucleotide pairs in each turn of helix as shown above :

Question 13.
What are harmones ? Give one example for each. [A.P. & T.S. Mar. 19, 18] [Mar. 14]
i) steroid hormones
ii) Poly peptide hormones and
iii) amino acid derivatives.
Answer:
Hormones : Hormone is defined as an “organic compound synthesised by the ductless glands of the body and carried by the blood stream to another part of the body for its function”.
Eg : testosterone, estrogen.

1. Example for steroid hormones : Testosterone, Estrogen
2. Example for poly peptide hormones : Insulin
3. Example for Amino acid derivative : Thyroidal hormones thyroxine.

Question 14.
Give the sources of the following vitamins and name the diseases caused by their deficiency (a) A (b) D (c) E and (d) K [A.P. Mar. 16, 15; T.S. Mar. 15]
Answer:

Long Answer Questions

Question 1.
Explain the classification of carbohydrates.
Answer:

Saccharides that reduce Fehling’s reagent, Tollen’s reagent are called reducing sugars.
Eg : glucose.
Saccharides that does not reduce these reagents are called non-reducing sugars.
Eg : sucrose.

Question 2.
Discuss the structure of glucose on the basis of its chemical propeties.
Answer:
1. The molecular formula of glucose is found to be C₆H₁₂O₆. It can be written as ‘CHO – (CHOH)₄ – CH₂OH’.

2. Acylation of glucose with acetic anhydride gives glucose pentacetate. Hence glucose molecule has five ‘-OH’ groups.

3. Glucose reacts with hydroxylamine and hydrogen cyanide forming corresponding oxime and cyano hydrin respectively. Hence glucose molecule has carbonyl group.

4. Glucose on oxidation with Tollen’s reagent and Fehling’s solution gives gluconic acid. Hence carbonyl group present in glucose is aldehydic group.

5. Glucose on oxidation with nitric acid gives glucaric’(saccharic) acid. This suggests that glucose molecule has primary alcoholic group (-CH₂OH)

6. On reduction with HI, glucose gives n – hexane.

This reaction suggests that all six carbons in glucose are linearly linked.

7. Open chain structure of glucose:
Based on above observations, glucose is given the open chain structure.

8. Objections against open chain structure of glucose :
Open chain structure of glucose could not explain

1. Why glucose does not respond to schiff s test.
2. Why it does not react with NaHSO₃ and NH₃.
3. Why there is mutarotation.

Mutarotation :
Change in specific rotation of a compound from certain value to fixed value is known as “Mutarotation”.
The specific rotation of α – glucose is + 110° and that of β – form is + 19.7°. If each of them is separately dissolved in water and allowed to stand, their specific rotation gradually change and reach to a specific constant value + 52.5°.

9. Cyclic structure of glucose :

These two structures have difference in configuration at ‘C₁‘ only and are called
ANOMERS.
Cyclic structure of glucose explains all the properties of glucose.

10. Pyranose structure of glucose :

Question 2.
Write notes on
a) fructose
b) sucrose
c) maltose
d) lactose
Answer:
a) Fructose :

• Fructose is an important ketohexose.
• It is formed by the hydrolysis of sucrose.
  
• It has the ketonic group at C – 2 and six carbons in straight chain as in the glucose.
• It has furanose ring structure.
• Open chain structures:
  
  α – D (-) – Fructo furanose structure
  β – D (-) – Fructo furanose structure
  Haworth structures :
  

b) Sucrose :
Sucrose is a disaccharide. It under go hydrolysis and forms equimolar mixture of D(+) – glucose arid D(-) fructose.
C₁₂ H₂₂ O₁₁ + H₂O → C₆ H₁₂ O₆ (glucose ) + C₆ H₁₂ O₆ (fructose)

In sucrose two monosaccharide units are held together by a glycosidic linkage between C- 1 of α – glucose and C – 2 of β – glucose.

Sucrose is a non reducing sugar.

During the hydrolysis of sucrose there is a change in the sign of rotation, from dextro (+) to laevo (-) and the product is named as invert sugar.

c) Structure of maltose :
Maltose is formed from two α – glucose units (Disaccharide)
C – 1 of one glucose linked to C – 4 of another glucose
It is a reducing sugar because C – 1 of 2^nd glucose is solution have free aldehyde group.

maltose on hydrolysis to form two glucose units
C₁₂ H₂₂ O₁₁ (Maltose) + H₂O → C₆ H₁₂ O₆ (Glucose ) + C₆ H₁₂ O₆ (Glucose)

d) Structure of lactose :

• Lactose is milk sugar
• Lactose is formed by the combination of β – glucose and β – galactose (Disaccharide).
• The linkage between C – 1 of galactose and c – 4 of glucose >
• It is a reducing sugar
  
• Lactose on hydrolysis to form glucose and galactose
  C₁₂ H₂₂ O₁₁ (Lactose) + H₂O → C₆ H₁₂ O₆ (glucose ) + C₆ H₁₂ O₆ (galactose)

Question 3.
Write notes on
a) starch
b) cellulose
c) importance of carbohydrates.
Answer:
a) Starch:
Polysaccharides : The saccharides which on hydrolysis to form large number of monosaccharides are called polysaccharides.
Eg : Starch and cellulose Starch :

• Starch is the most important dietary source for human beings.
• Vegetables, roots, cereals are important sources of starch.
• It is a polymer of a – glucose.
• It is constituted by two components Amylose and amylopectin

Amylose :

• It constitutes 15 – 20% of starch -4 Anylose is water soluble component.
• Amylose is a branched chain with 200 – 1000 α – D – glucose units held by C – 1 to C – 4 glycosidic linkage.

Amylopectin :

• Amylopectin constitutes 80 – 85% of starch.
• It is a branched chain polymer of a – glucose units in which chain is formed by C – 1 to C – 4 glycosidic linkage whereas branching occurs by C – 1 to C – 6 glycosidic linkage.

b) Cellulose :

• Cellulose occurs in plants and it is the most abundant organic substance.
• It is a major constituent of cell wall of plant cells.
• Cellulose is a straight chain polysaccharide composed only of β – D – glucose units – which are joined by glycosidic linkage between C – 1 of one glucose and C – 4 of the next glucose.

c) Importance of carbohydrates :

• Carbohydrates are essential for life of plants.
• Carbohydrates are used as storage molecules as starch in plants.
• Cell wall of plants is made up of cellulose.
• Carbohydrates are also essential for life of animals. Carbohydrates are used as storage molecules as glycogen in animals.
• Carbohydrate source honey is used for a long time as an instant source of energy.

Question 4.
Write notes on amino acids.
Answer:
The organic compounds which contain amino (-NH₂) functional group and carboxyl (-COOH) functional group are called amino acids.
Eg : Glycine, Alanine etc.

Essential amino acids : The amino acids that cannot be synthesised by the body and must be supplied in the diet are called essential amino acids.
Eg : valine, leucine, phenyl alanine etc.,

Non-essential amino acids : Other amino acids synthesised by the tissues of the body are called non-essential amino acids.
Eg : Glycine, alanine etc.,

Zwitter ion : In aqueous solution Of amino acids, the carboxyl group can lose a proton and amino acid can accept that proton to form a dipolar ion. This is called as zwitter ion.

Peptide linkage :
Amide linkages between amino acids are known as peptide linkages. The product obtained from two amino acid molecules through peptide bond is called a dipeptide. Peptide chain may be extended to many amino acids.
Proteins are naturally occufing polypeptides that contain more than 50 amino acid units.

Question 5.
Write notes on proteins.
Answer:
Proteins : A poly peptide with more than hundred amino acid residues, having molecular mass higher than 10,000 units is called a protein.
g : keratin, myosin, insulin.
With respect to peptide bond proteins classified into two types.

1. Fibrous proteins
2. Globular proteins.

When the chains of polypeptides coil around to give a spherical shape then globular proteins are formed. These are usually soluble in water.
Eg : insulin and albumins.

When the poiy peptide chains run parallel and are held together by hydrogen and disulphide bonds then fibre – like structure is formed. These are called fibrous proteins. These are insoluble in water.
Eg: keratin, myosin.

Protein Denaturation: The phenomenon of disorganization of native protein structure is known as denaturation. Denaturation results in the loss of secondary; tertiary,. nad quaternary structure of proteins. This involves a change in physical, chemical and biological properties of protein molecules.

Agents of denaturation:
Physical agents – Heat, violent shaking, X – rays, Uy – radiation
Chemical agents – Acids, alkalies, organic solvénts, urea, salts of heavy metals.
Protein strúctures and shapes are studied at four different levels as:
i) Primary
ii) Secondary
iii) Tertiary
iv) Quaternary structures

i) Primary structure: The primary structure of protein is defined as the linear sequence of amino acid residues making up its polypeptide chain. Proteins may be formed of one or more polypeptide chains. The amino acid residues are linked by peptide bonds, The peptide bond is formed between carboxyl group of one amino açid and amino group of adjacent amino acid.
Eg: fibroin of silk.

R₁ – amino acid 1
R₂ – amino acid 2

ii) Secondary structure : The secondary structure explains the shape of the polypeptide chain. It is derived from the primary structure by the formation of hydrogen bond interactions between amino acid residues.

Disulfide bonds also occur either in same chain or between polypeptide chains. The secondary structure is classified into two types namely helical structure and pleated sheets.
Eg. : Keratin of hair

iii) Tertiary structure i Tertiary structure is exhibited by proteins having only one polypeptide chain. The three dimensional structure of a protein is referred to as tertiary structures. Fibrous and globular proteins are formed by tertiary structures. Various bonds are responsible for tertiary structure.

1. Hydrophobic interactions
2. Hydrogen bonds
3. Disulphide bonds (- CH2 – S – S – CH2 -)
4. Ionic or electrostatic interactions
5. Vander Waal forces
   e.g : Myoglobin, Ribonuclease

iv) Quaternary structure : Two or more poly- peptide chains associate together to protect quaternary structure. A protein with a quaternary structure is referred to as an oligomes.
Eg. : Hemoglobin a chain

Question 6.
Write notes on
(a) enzymes and
(b) vitamins.
Answer:
Enzymes :
The group of complex proteinoid organic compounds, elaborated by living organism which catalyse specific organic reactions are called enzymes. Eg.: Lipases, Rennin, Maltase, Invertase etc. Practically all biological processes such as digestion, respiration etc., are carried on through the agency of enzymes.
Enzymes may be defined as biocatalysts synthesised by living cells.
The functional unit of enzyme is known as holo enzyme made up at apo enzyme (protein part) and co enzyme (non-protein part)

b) Vitamins :
Vitamin is defined as an “accessory food factor which is essential for growth and healthy maintenance of the body.”
Classification : Vitamins are broadly classified into two major groups.
a) the fat soluble Eg : vitamin A, D, E and K.
b) water soluble Eg : vitamin B – complex and C.

Question 7.
Explain the structures of DNA and RNA.
Answer:
Structure of DNA : To understand the structure of DNA, we should know the charagaff s rule, which states that :

1. Base composition on DNA for a particular organism is constant throughout all the somatic cells.
2. Base composition always varies from one organism to another and is expressed by the dissymmetry ratio \(\frac{(\mathrm{A}+\mathrm{T})}{(\mathrm{G}+\mathrm{C})}\)
3. Organisms closely related to each other often have similar base composition and hence have closed values for their dissymmetry ratios.
4. In a given organism the amount of adenine is always equal to the amount of thymine (A = T) and amount of guanine is equal to amount of cytosine (G = C).
5.  In a given organism the total amount of purine bases are always equal to total number of pyrimidine bases (i.e.,) (A + G = T + C).

M. Wilkins found that within the crystal there is a repeat distance of 3.4 nm and there are ten subunits per turn.

Watson – Crick model for DNA : From the above observations Watson and Crick constructed a model for DNA.
This model consists of two right handed polynucleotide chains that are complimentary and coiled about the same axis to form double-helix. Some specific base pairs can be spatially accommodated and these are A – T and G – C pairs. The bases are closely associated with each other by hydrogen bonding.

The helix has diameter of about 2.0 nm and contains 10 nucleotide pairs in each turn of helix as shown above :

Structure of RNA: The native RNA is single stranded rather than a double stranded helical structure characteristic of DNA. However, given the complementary base sequence with opposite polarity, the single strand of RNA may fold back on itself like a hairpin and thus acquire double stranded pattern. In the region of hairpin loops, “A” pairs with ‘U’ and ‘G’ pairs with ‘C’. The base pairing in RNA hairpins is frequently imperfect. The proportion of helical regions in various types of RNA varies over a wide range.

Question 8.
Write notes on the functions of different hormones in the body.
Answer:
Functions of Hormones :

• Hormones help to maintain the balance of biological activities in the body.
• Insulin maintains the blood glucose level with in the limit.
• Growth hormones and sex hormones play role in growth and development.
• Low level of thyroxine (produced from thyroid gland) causes hypothyroidism. High level of thyroxine causes hyper thyroidism. .
• gluco corticoids control the carbohydrate metabolism, modulates the inflammatory reactions.
• The mineralo corticoids control the level of excretion of water and salt by the kidney.
• Adrenal cortex does not function properly then results in Addison’s disease.
• Hormones released by gonads are responsible for development of secondary sex characters.
• Testosterone is responsible for development of secondary sex hormone produced in male.
• Estradiol is the main female sex hormone responsible for development of secondary female characterstics like control of menustrual cycle.
• Progesterone is responsible for preparing the uterus for implantation of fertilised egg.

Intext Questions

Question 1.
Glucose or sucrose are soluble in water but cyclohexane and benzene (simple six membered ring compounds) are insoluble in water. Explain.
Answer:
In glucose (C₆H₁₂O₆), 5 – OH groups are present and in sucrose (C₁₂H₂₂O₁₁), B – OH groups are present, which are polar in nature. They are involved in intermolecular hydrogen bonding with water molecules, so these compounds are readily soluble in water.

Benzene (C₆H₆) and cyclohexame (C₆H₁₂) are hydrocarbons. They do not have any polar group so they cannot make hydrogen bonds with water. Therefore, they are insoluble in water.

Question 2.
What are the expected products of hydrolysis of lactose ?
Answer:
Lactose forms two molecules of monosaccharides on hydrolysis – One molecule of D-(+) – glucose and one molecule of D – (+) – galactose.

Question 3.
How do you explain the formation of furanose structure for fructose while glucose forms pyranose structure with same molecular formula C₆H₁₂O₆ ?
Answer:
D-glucose, an aldohexose given the characteristic reactions of aldehydic group (e.g., with HCN Tollen’s reagent, Fehling reagent etc.,) but penta acetae of D-glucose does not give these reactions. It means that either – CHO group is absent or it is not available for the chemical reactions in penta acetyl glucose. Infact, the aldehydic group is a part of hemiacetal structure which penta acetyl glucose has. So, it is not available for reaction.

Question 4.
The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.
Higher the polarity of a group, more is its solubility in water.
Answer:
Amino acids are dipolar in nature (N⁺ H₃ – CHR – COO^–) and have strong dipolar interatctions.
Therefore, these have high melting points. When dissolved in water, these form hydrogen bonds with water molecules, therefore, these are soluble in water, (except at isoelectric point, where they have least solubility) In case of halo acids, these are not dipolar. Only their carboxyl group is involved in hydrogen bonding, not the halogen atom. Therefore, halo acids, have lower melting points and lesser solubility than amino acids.

Question 5.
Why cannot vitamin C be stored in our body ?
Answer:
VitaminC (ascorbic acid) is water soluble. Therefore, it is regularly excreted in urine from the body and cannot be stored.

Question 6.
What products would be formed when a nucleotide from DNA containing thymine is hydrolysed ?
Give the composition of DNA molecule as on hydrolysis it gives its all constituents.
Answer:
When a nucleotide from DNA is hydrolysed, it will give deoxyribose sugar molecules, phosphoric acid, pyrimidine bases, i.e., guanine (G) and adenine (A) and purine bases, i.e., thymine (T) and cytosine (C).

Question 7.
When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained. What does this fact suggest about the structure of RNA ?
Single stranded structure of RNA.
Answer:
DNA molecule has a double strand structure and four complementary bases paired with each other. Cytosine (C) pairs with guanine (G) while thymine (T) pairs with adenine (A). Due to such structure, DNA produces the products in definite molar ratio.

The case is not same in RNA, ie., base pairing rule is not followed. Thus, when RNA is hydrolysed, the quantities of different bases are different. This suggests that RNA has single stranded structure.

Andhra Pradesh BIEAP AP Inter 2nd Year Chemistry Study Material 8th Lesson Polymers Textbook Questions and Answers.

AP Inter 2nd Year Chemistry Study Material 8th Lesson Polymers

Very Short Answer Questions

Question 1.
Define the terms monomer and polymer.
Answer:
Monomer : The repeating structural units of polymer which are derived from simple and reactive molecules linked to one another by covalent bonds are called monomers.

Polymer : A large molecular weight complex compound which is formed by the.repeated combination of simple units (monomers) is called polymer.

Question 2.
What are polymers ? Give example.
Answer:
Polymer : A large molecular weight complex compound which is formed by the repeated combination of simple units (monomers) is called polymer.
E.g. : Nylon 6, 6, Buna-S,. rubber etc…..

Question 3.
What is polymerization ? Give an example of polymerization reaction.
Answer:
Polymerization: The process of formation of polymers from respective monomers is called polymerization.
(or)
A large molecular weight complex compound which is formed by the repeated combination of simple units is called polymer. This process is called polymerisation.
E.g. : Formation of polyethene from ethene and reaction of hexamethylene diamihe and adipic acid leading to the formation of Nylon 6, 6 are examples of two different types of polymerisation reactions.

Question 4.
Give one example each for synthetic and semi-synthetic polymers.
Answer:
Examples of synthetic polymers : Neoprene, Buna-S, Buna-N
Examples of Semi synthetic polymers : Cellulose rayon, cellulose nitrate.

Question 5.
How are the polymers classified on the basis of structure ?
Answer:
On the basis of structure, polymers are classified into three types :

1. Linear polymers : These contains long and straight chains.
   E.g.: PVC, polythene (high density) etc.
2. Branched chain polymers : These contains linear chains having some branches.
   E.g.: low density polythene.
3. Cross linked polymers (or) Network polymers : These are usually formed from bi functional and tri functional monomers and contain strong covalent bonds between various linear polymer chains.
   E.g.: Bakelite, melamine etc. .

Question 6.
Give one example each for linear and branched chain polymers.
Answer:

1. Linear polymers : These contains long and straight chains.
   E.g.: PVC, polythene (high density) etc.
2. Branched chain polymers : These contains linear chains having some branches.
   E.g. : low density polythene.

Question 7.
What are cross linked (or network) polymers ? Give example.
Answer:
Cross linked polymers (or) Network polymers: These are usually formed from bi functional and tri functional monomers and contain strong covalent bonds between various linear polymer chains. E.g. : Bakelite, melamine etc.

Question 8.
What is addition polymer ? Give example. [T.S. Mar. 15]
Answer:
Addition Polymer: The polymer which is formed by the addition of molecules of monomers of same type (or) different type containing double bonds is called addition polymer.
E.g.: Polyethene, poly acrylonitrile.

Question 9.
What is condensation polymer ? Give example.
Answer:
Condensation polymer : The polymer which is formed by the condensation reaction between molecules having more than one functional group is called condensation polymer.
E.g.: Nylon 6, 6, Poly ethylene terephthalate.

Question 10.
What are homopolymers ? Give example.
Answer:
Homopolymers : The polymers which are formed by the polymerisation of a single monomeric species are known as homopolymers. E.g.: Polyethene, Poly styrene.

Question 11.
What are copolymers ? Give example.
Answer:
Copolymers : A polymer which is formed by the polymerisation of two (or) more chemically different types of monomer units is called copolymer. E.g.: Butadiene – Styrene polymer (Buna-S)

Question 12.
Is – [-CH₂ – CH (C₆H₅)-]_n – a homopolymer or a copolymer ?
Answer:
-[-CH₂ – CH (C₆H₅-]_n is polystyrene. It is a homopolymer.
It is formed by the polymerisation of single monomer styrene.
(C₆H₅ – CH = CH₂)

Question 13.
Is (NH – CHR- CO)_n a homopolymer or a copolymer ?
Answer:
[NH – CHR – CO]_n is a homopolymer. It is formed by the polymerisation of single monomer a-amino acid (NH₂ – CHR-COOH).

Question 14.
What are the classes of the polymer based on molecular forces ?
Answer:
On the basis of molecular forces polymers are classified into four types.

1. Elastomers: These are rubber like solids with elastic properties.
   E.g.: Buna-S, Buna-N.
2. Fibres : Fibres are the thread forming Solids which possess high tensile strength.
   E.g. : Nylon 6, 6, polyesters
3. Thermoplastic Polymers : These are the linear (or) slightly branched long chain
   molecules capable of softening on heating and hardening on cooling.
   E.g.: Polystyrene, polythene.
4. Thermo setting polymers : These polymers are cross linked (or) heavily branched molecules which on heating undergo extensive cross linking in moulds and again become infusible.
   E.g. : Bakelite, urea-formaldehyde resin etc….

Question 15.
What are elastomers ? Give example. .
Answer:
Elastomers: These are rubber like solids with elastic properties. In elastomers the polymer chains are held together by the weak inter molecular forces.
E.g.: Buna – S, Buna – N etc.

Question 16.
What are fibres ? Give example.
Answer:
Fibres : Fibres are the thread forming solids which possess high tensile strength.
E.g.: Nylon 6, 6, polyesters

Question 17.
What are thermoplastic polymers ? Give example.
Answer:
Thermoplastic Polymers: These are the linear (or) slightly branched long chain molecules capable of softening on heating and hardening on cooling.
E.g.: Polystyrene, polythene.

Question 18.
What are thermosetting polymers ? Give example.
Answer:
Thermo setting polymers: These polymers are cross linked (or) heavily branched molecules which on heating undergo extensive cross linking in moulds and again become infusible.
E.g.: Bakelite, urea-formaldehyde resin etc….

Question 19.
Write the name and structure of one of the common initiators used in free radical polymerization reaction.
Answer:
One of the common initiator used in free radical – polymerisation reaction is benzoyl peroxide.
Structure:

Question 20.
How can you differentiate between addition and condensation polymerization?
Answer:

Addition polymerisation

1. Monomers used are unsaturated com­pounds.
2. Polymer formation takes place without loss of atoms (or) groups.
3. It is chain growth polymerisation.
4. These polymers are called addition (or) ‘ chain (or) vinyl polymers.

Condensation polymerisation

1. Monomers are bifunctional, tri-functional compounds.
2. Polymer formation takes place with loss of atoms (or) groups like NH₃, H₂0 etc.
3. It is step growth polymerisation.
4. These are called condensed polymers.

Question 21.
What is Ziegler – Natta catalyst? [T.S. Mar. 19]
Answer:
A mixture of Tri alkyl aluminium and titanium chloride is called Ziegler – Natta catalyst
E.g.: (C₂H₅)₃ Al + TiCl₄

Question 22.
How is Dacron obtained from ethylene glycol and terepthalic acid?
Answer:
Formation of dacron is an example of condensation polymerisation. It is obtained from ethylene glycol and terephthalic acid as follows.

Question 23.
What are the repeating monomeric units of Nylon 6 and Nylon 6, 6?
Answer:
The repeating monomeric units of Nylon – 6 is Capro lactam

The repeating monomeric units of Nylon 6, 6 are hexamethylene diamine and Adipic acid.
H₂N-(CH₂)₆ – NH₂
Hexamethylene
HOOC – (CH₂)₄ – COOH
Adipic acid

Question 24.
What is the difference between Buna – N and Buna – S ?
Answer:
Buna – N : Buna – N is the copolymer which is formed by the polymerisation of 1, 3 – Butadiene and acrylonitrile.

Question 25.
Arrange the following polymers in increasing order of their molecular forces.

1. Nylon 6, 6 Buna – S, Polythene
2. Nylon 6, Neoprene, Polyvinyl chloride

Answer:

1. Increasing order of inter molecular forces of given polymers is
   Buna – S < polythene < Nylon -6, 6
2. Increasing order of inter molecular forces of given polymers is
   Neoprene < polyvinyl chloride < Nylon – 6.

Question 26.
Identify the monomer in the following polymeric structures

Answer:

1. Monomers present in are decane dioic acid HOOC -CH₂-)₈ COOH and hexamethylene diamine H₂N – (CH₂-)₆ NH₂
2. Monomers present in (-NH – CO – NH – CH₂ -)_n are urea CO (NH₂)₂, formaldehyde HCHO.

Question 27.
Name the different types of molecular masses of polymers.
Answer:
The different types of important molecular masses of polymers are

1. Number average molecular mass (\(\overline{\mathbf{M}}_{\mathrm{n}}\))
2. Weight average molecular mass (\(\overline{\mathbf{M}}_{\mathrm{w}}\))

Question 28.
What is PDI (Poly Dispersity Index) ? [A.P. Mar. 19]
Answer:
Poly Dispersity Index (PDI) : The ratio between weight average molecular mass (\(\overline{\mathbf{M}}_{\mathrm{w}}\)) and the number average molecular mass (\(\overline{\mathbf{M}}_{\mathrm{n}}\)) of a polymer is called Poly Dispersity Index (PDI).

Question 29.
What is vulcanization of rubber ? [T.S. Mar. 19, 16; A.P. Mar. 17]
Answer:
Vulcanization of rubber : The process of heating the raw rubber with sulphur (or) with sulphur compounds to improve it’s physical properties is called vulcanization of rubber.

Question 30.
What is the cross linking agent used in the manufacture of type rubber ?
Answer:
In the manufacture of tyre rubber 5% sulphur is used as cross linking agent. ‘

Question 31.
What is biodegradable polymer ? Give one example of a biodegradable polyester ?
Answer:
Biodegradable poiymers : The polymers degradable by enzymatic hydrolysis and to some extent by oxidation are called biodegradable polymers.
E.g. : Nylon – 2, Nylon – 6, PHBV, Polyglycolic acid, Polylactic acid etc.

Question 32.
What is PHBV ? How is it useful to man ? [A.P. Mar. 19, 18, 16; T.S. Mar. 18, 16, 15]
Answer:
Poly β – hydroxy butyrate – CO – β – hydroxy Valerate (PHBV) : It is a Copolymer of 3 -hydroxy butanoic acid and 3 – hydroxy pentanoic acid.

Properties & Uses : The properties of PHBV vary according to the ratio of both the acids, 3-hydroxy butanoic acid provides stiffness and 3-hydroxy pentanoic acid imparts flexibility to copolymer.
It is used in medicine for making capsules.
PHBV also undergoes degradation by bacteria.

Question 33.
Give the structure of nylon 2 – nylon 6 ?
Answer:
Nylon 2 – Nylon 6 :
an alternating polyamide copolymer of glycine ( – COOH) and amino caproic acid (H₂N – CH₂)₅ – COOH). It is a biodegradable polymer.
Structure of Nylon 2 – Nylon – 6

Short Answer Questions

Question 1.
Classify the following into addition and condensation polymers [A.P. Mar. 16]
i) Terylene
ii) Bakelite
iii) Polyvinyl chloride
iv) Polythene
Answer:
i) Terylene is a condensation polymer.
ii) Bakelite is a condensation polymer
iii) Polyvinyl chloride is an addition polymer
iv) Polythene is an addition polymer.

Question 2.
How do you explain the functionality of a polymer ?
Answer:
The number of bonding sites present in the monomers of the polymer is called functionality.
E.g.:

1. Functionality of ethene, propene is one.
2. Functionality of ethylene glycol is two.

Question 3.
Distinguish between the terms homo polymer and co polymer. Give one example of each.
Answer:
Homopolymers : The polymers which are formed by the polymerisation of a single monomeric species are known as homopolymers.
E.g. : Polyethene; Poly styrene.
Copolymers: A polymer which is formed by the polymerisation of two (or) more chemically different types of monomer units is called copolymer.
E.g.: Butadiene – Styrene polymer (Buna-S)

Question 4.
Define thermoplastics and thermosetting polymers with two examples of each.
Answer:
Thermoplastic Polymers : These are the linear (or) slightly branched long chain molecules capable of softening on heating and hardening on cooling. E.g. : Polystyrene, polythene.
Thermo setting polymers: These polymers are cross linked (or) heavily branched molecules which on heating undergo extensive cross linking in moulds and again become infusible.
Eg.: Bakelite, urea-formaldehyd, resin etc….

Question 5.
Explain copolymerization with an example.
Answer:
Copolymers: A polymer which is formed by the polymerisation of two (or) more chemically different types of monomer units is called copolymer.
E.g.: Butadiene-Styrene polymer(Buna-S)
The process of formation of copolymer is called copolymerisation.
E.g. : Buna – S : Buna – S is the copolymer which is formed by the polymerisation of 1,3- Butadiene and Styrene.

Question 6.
Explain free radical mechanism for the polymerization of ethene.
Answer:
Polymerisation of ethene to polythene proceeds through free radical mechanism. The initiator used in this reaction is benzoyl peroxide. This mechanism involves three steps.
1) Chain initiation : The addition of phenyl free radical formed by the peroxide to the ethene double bond and forms a larger free radical.

C₆H₅ + CH₂ = CH₂ → C₆H₅ – CH₂ – CH₂

2) Chain propagation : The above formed radical reacts with another molecule of ethene another bigger sized radical is formed. The repetetion of this sequence takes places.

3) Chain Termination : The product radical formed reacts with another radical to form polymerised product.

Question 7.
Write the names and structures of the monomers used for getting the following polymers . [Mar. 14]
i) Polyvinyl chloride
ii) Teflon
iii) Bakelite
iv) Polystyrene.
Answer:
i) Polyvinyl chloride
Monomer : Vinyl chloride
Structure : CH₂ = CH – Cl

ii) Teflon
Monomer : Tetrafluoro ethylene
Structure : CF₂ = CF₂

iii) Bakelite
Monomers : Phenol, Formal dehyde
Structure :

iv) Polystyrene
Monomer : Styrene
Structure :

Question 8.
Write the names and structures of the monomers of the following polymers.
i) Buna – S
ii) Buna – N
iii) Dacron
iv) Neoprene
Answer:
i) Buna – S
Monomers : 1,3- Butadiene, Styrene
Structure :

ii) Buna – N
Monomers : 1,3- Butadiene, Acrylonitrile
Structure : CH₂ = CH – CH = CH₂, CH₂ = CH – CN

iii) Dacron
Monomers : Ethylene glycol, Terephthalic acid
Structure : HOCH₂ – CH₂OH, C HOOC COOH

iv) Neoprene
Monomers : 2 – chloro -1,3- Butadiene
Structure :

Question 9.
What is natural rubber ? How does it exhibit elastic properties ?
Answer:

1. Natural rubber is a polymer and possesses elastic properties.
2. It is an elastomer and it is manufactured from rubber latex. Latex is a colloidal dispersion of rubber in water.
3. Natural rubber may be considered as a linear polymer of isoprene. It is also called as cis-1, 4-Poly isoprene.
4. The cis poly isoprene molecule consists of various chains held together by weak vander waals interactions and has a colloid structure. Thus it stretches like a spring and exhibits elastic properties.

Question 10.
Explain the purpose of vulcanization of rubber. [T.S. Mar. 17]
Answer:

1. Natural rubber becomes soft at high temperatures and brittle at low temperatures. It shows high water absorption capacity.
2. Natural rubber is soluble in non-polar solvents and is non-resistant to oxidising agents.
3. To improve these physical properties rubber can be vulcanised.
4. The process of heating the raw rubber with sulphur (or) with sulphur compounds to improve it’s physical properties is called vulcanisation of rubber.
5. The vulcanized rubber has improved properties like elasticity, minimum water absorbing tendency, high resistance to chemical oxidation as well as organic solvents.

Question 11.
Explain the difference between natural rubber and synthetic rubber.
Answer:
Natural rubber : The rubber which is obtained from natural sources such as plants and animals rubber called natural rubber. E.g.: Starch, cellulose, rubber etc.

Synthetic rubber : The rubber which are artificially prepared i.e. man-made are called synthetic rubbers.
These have wide applications in daily life as well as in industry.

Question 12.
How does the presence of double bonds in rubber molecules influence their structure and reactivity ?
Answer:

1. Natural rubber is cis. poly isoprene. It is obtained by polymerisation of isoprene. The polymerisation takes place at 1, 4 positions. .
2. In rubber molecule double bonds are located between C₂ and C₃ of the monomer
   isoprene.
3. These double bonds (cis) do not allow the polymer chain to come closer. Therefore only weak vander waal’s forces are present.
4. The chains are not linear, they can be stretched just like springs and exhibits elastic properties.

Question 13.
What are LDP and HDP ? How are they formed ?
Answer:
Polythenes are two types : .

1. LDP (Low Density Polythene),
2. HDP (High Density Polythene)

1) Low Density Polythene : LDP is formed by the polymerisation of ethene under high pressure of 1000 to 2000 atm. at a pressure of 350 to 570K in the presence of traces of dioxygen (or) a peroxide initiator.
Properties :
a) This is obtained through the free radical addition.
b) LDP is chemically inert and tough.
c) LDP is flexible and a poor conductor of electricity.
Uses:
a) It is used in the insulation of electric cables.
b) It is used in the manufacture of pipes in agriculture irrigation.

2) High Density Polythene : HDP is formed by the polymerisation of ethene in a hydro carbon solvent in presence of Ziegler Natta catalyst at a temperature of’333K to 343 K and under a pressure of 6 – 7 atm
Properties :
a) HDP consists of linear molecules and has high density due to close packing.
b) It is chemically inert and more tough, hard.
Uses:
a) It is used in manufacture of house hold articles like buckets, dustbins etc.
b) It is used in manufacture of pipes.

Question 14.
What are natural and synthetic polymers ? Give two examples of each type.
Answer:
Natural polymers : The polymers which are obtained from natural sources such as plants and animals are called natural polymers.
E.g.: Starch, cellulose, rubber etc.

Synthetic polymers: The polymers which are artificially prepared i.e. man-made are called synthetic polymers.
These have wide applications in daily life as well as in industry.
E.g.: Plastics, Nylon 6, 6, synthetic rubbers.

Question 15.
Write notes on different types molecular masses of polymers.
Answer:
The molecular mass of the polymer doesnot remain constant as in the case of simple chemical substances. So the molecular weight of a polymer is expressed in terms Of “average value”.
The average molecular masses of polymers expressed in different ways. The following are the important among them.

1. Number average molecular mass (\(\overline{\mathrm{M}}_{\mathrm{n}}\)),
2. Weight average molecular mass (\(\overline{\mathrm{M}}_{\mathrm{w}}\))

i) Number average molecular mass (\(\overline{\mathrm{M}}_{\mathrm{n}}\)) : If a polymer sample contains N₁ particles of mass M₁ each and N₂ particles of Mass M₂ each and so on.
The number average molecular weight (\(\overline{\mathrm{M}}_{\mathrm{n}}\)) of the polymer = \(\frac{\sum_{\mathrm{n}_{\mathrm{i}}=1}^{\infty} \mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}}{\sum_{\mathrm{n}_{\mathrm{i}}=1}^{\infty} \mathrm{N}_{\mathrm{i}}}\)
(\(\overline{\mathrm{M}}_{\mathrm{n}}\)) can be determined by end group analysis method (or) physical methods based on the number of particle present.

ii) Weight average molecular weight (\(\overline{\mathrm{M}}_{\mathrm{w}}\)) : Weight average molecular weight (\(\overline{\mathrm{M}}_{\mathrm{w}}\)) is calculated by multiplying the molecular weight of each type of particle with contribution of the species to the total weight of the sample.
Weight average molecular weight (\(\overline{\mathrm{M}}_{\mathrm{w}}\)) of the polymer = \(\frac{\sum_{n_{i}=1}^{\infty} N_{i} M_{i}^{2}}{\sum_{n_{i}=1}^{\infty} N_{i} M_{i}}\)

Long Answer Questions

Question 1.
Write an essay on i) Addition polymerization and ii) Condensation polynerization
Answer:
i) Addition Polymerization : Addition polymerization involves the self addition of unsaturated monomers without loss of any small molecules to form polymer.
The polymer so formed is called addition polymer.
This polymerisation is also called chain growth polymerisation.
In addition polymerisation, monomers should contain double bonds.
This type of polymerisation can be broadly subdivided into 2 groups.
a) ionic polymerisation (cationic & anionic)
b) free radical polymerization
Addition polymerization mechanism involves three steps. They are : i)-Chain initiation step ii) Chain propagation step and iii) Chain termination step.
E.g. : Vinyl Chloride molecules polymerises to PVC.

ii) Condensation polymerization : In this polymerisation monomers combine together with the loss of simple molecules like H₂O, NH₃ etc. The formed polymer is called condensation polymer.
Condensation polymers are generally derived from di (or) polyfunctional monomers. This polymerization is also called step polymerization.
E.g.: i) Nylon – 6,6 is formed from hexamethylene diamine and adipic acid by condensation.

ii) Polyethylene terephthalate (PET) from ethylene glycol and terephtholic acid by condensation reaction.

Question 2.
Explain the classification of polymers based on their source and structure.
Answer:
On the basis of source polymers are classified into three types.

1. Natural polymers
2. Semi synthetic polymers
3. Synthetic polymers

1) Natural polymers : The polymers which are obtained from natural sources such as plants and animals are called natural polymers.
E.g.: Starch, cellulose, rubber etc.

2) Semi synthetic polymers : The polymers which are synthetic derivatives of the natural polymers are called semisynthetic polymers.
E.g. : Cellulose rayon, cellulose nitrate.

3) Synthetic polymers : The polymers which are artificially prepared i.e. man-made are called synthetic polymers. .
These have wide applications in daily life as well as in’ industry.
E.g.: Plastics, Nylon 6, 6, synthetic rubbers.

Classification of polymers on the basis of structure :
i) Linear polymers : It is one in which the repeating units are similar to the links in a very long chain.

E.g.: Polythene, PVC etc.

ii) Branched chain polymers : It is one in which some of the molecules are attached as side chains to the linear chains.

E.g.: Low density polythene (LDPE) etc.

iii) Cross linked (or) network polymers : More branching at random points connecting many chains give rise to network (or) cross linked polymers.

E.g.: Bakelite, melamine etc.

Question 3.
Explain the classification of polymers based on the mode of polymerization and nature of molecular forces.
Answer:
On the basis of mode of polymerisation polymers are classified into two types :
1) Addition polymers
2) Condensation polymers.
1) Addition Polymer : The polymer which is formed by the addition of molecules of monomers of same type (or) different type containing double bonds is called addition polymer.
Eg.: Polyethene, poly acrylonitrile.
2) Condensation polymer : The polymer which is formed by the condensation reaction between molecules having more than one functional group is called condensation polymer.
Eg.: Nylon 6, 6, Poly Ethylene terephthalate.

On the basis of molecular forces polymers are classified into four types.

1. Elastomers : These are rubber like solids with elastic properties.
   Eg.: Buna-S, Buna-N.
2. Fibres : Fibres are the thread forming solids which possess high tensile strength.
   Eg.: Nylon 6, 6, polyesters.
3. Thermoplastic Polymers : These are the linear (or) slightly branched long chain molecules capable of softening on heating and hardening on cooling.
   Eg.: Polystyrene, polythene.
4. Thermo setting polymers : These polymers are cross linked (or) heavily branched molecules which on heating undergo extensive cross linking in moulds and again become infusible.
   Eg.: Bakelite, urea-formaldehyde resin etc….

Question 4.
What are synthetic rubbers ? Explain the preparation and uses of the following
i) Neoprene
ii) Buna-N
iii) Buna-S.
Answer:
The polymer which is capable of getting stretched almost to double the length and which is also vulcanizable as in the case of natural rubber is called a synthetic rubber.
1) These are homo polymers of 1, 3 – butadiene derivatives (or) copolymers in which one of the monomer is 1, 3 – Butadiene (or) its derivatives and the other is any unsaturated monomer.
2) Synthetic rubber return to its original shape and size when the stretched force is removed.
Eg.: Neoprene, Buna – S, Buna – N.

i) Neoprene : Neoprene is formed by the free radical polymerisation of chloroprene (2-Chloro 1, 3 – Butadiene)

Uses:
1) It has superior resistance to vegetable and animal oils.
2) It is used in the manufacture of gaskets, conveyor belts.

ii) Buna – N : Buna – N is the copolymer which is formed by the polymerisation of 1, 3 – Butadiene and acrylonitrile.

Uses:
1) It is resistant to the action of petrol, lubricating oil and organic solvents.
2) It is used in. making oil seals, tank lining.

iii) Buna – S : Buna – S is the copolymer which is formed by the polymerisation of 1, 3 – Butadiene and Styrene.

Uses :
1) It is a good substitute for natural rubber.
2) It is used in manufacture of auto tyres.
3) It is used in manufacture of floor tiles.
4) It is used in manufacture of foot wear components, cable insultation

Textual Examples

Question 1.
Is [-CH₂ – CH (C₆H₅-)] _n a homopolymer or a copolymer ?
Solution:
It is a homopolymer and the monomer from which it is obtained is styrene C₆H₅CH = CH₂.

Question 2.
A polymer contains 10 molecules with molecular mass 10,000 and 10 molecules with molecular mass 1,00,000. Calculate number – average molecular mass.
Solution:
\(\overline{\mathrm{M}}_{\mathrm{n}}=\frac{\sum \mathrm{N}_{\mathrm{i}} \mathrm{M}_{\mathrm{i}}}{\sum \mathrm{N}_{\mathrm{i}}}=\frac{10 \times 10000+10 \times 100000}{10+10}\) = 55,000

Intext Questions

Question 1.
What are polymers ?
Answer:
Polymers are high molecular mass substances consisting of large -number of repeating structural units. They are also called as macromolecules. Some examples of polymers are polythene, bakelite, rubber, nylon 6, 6 etc.

Question 2.
How are polymers classified on the basis of structure ?
Answer:
On the basis of structure, the polymers are classified as below :

1. Linear polymers such as polythene, polyvinyl chloride, etc.
2. Branched chain polymers such as low density polythene.
3. Cross linked polymers such as bakelite, melamine, etc.

Question 3.
Write the names of monomers of the following polymers.

Answer:

1. Hexamethylene diamine and adipic acid
2. Caprolactam
3. Tetrafluoroethene.

Question 4.
Classify the following as addition and condensation polymers : Terylene, Bakelite, Polyvinyl chloride, polythene.
Answer:
Additon polymers : Polyvinyl chloride, polythene. Condensation polymers : Terylene, Bakelite.

Question 5.
Explain the difference between Buna – N and Buna – S. .
Answer:
Buna – N is a copolymer of 1, 3 – butadiene and acrylonitrile and Buna-S a copolymer of 1, 3—butadiene and styrene.

Question 6.
Arrange the following polymers in increasing order of their intermolecular forces.
i) Nylon 6, 6 Buna — S, Polythene. ii) Nylon 6, Neoprene, Polyvinyl chloride.
Answer:
In order of increasing intermolecular forces.

1. Buna—S, Polythene, Nylon 6, 6.
2. Neoprene, Polyvinyl chloride, Nylon 6.