Students can go through AP Board 7th Class Science Notes 2nd Lesson Nature of Substances to understand and remember the concept easily.
AP Board 7th Class Science Notes 2nd Lesson Nature of Substances
→ Substances can be classified into acids, bases and neutral.
→ Acids are sour in taste. Ex: Hydrochloric acid, sulphuric acid and nitric acid.
→ Bases are bitter in taste and slippery to touch. Ex: Sodium hydroxide, magnesium hydroxide, potassium hydroxide and calcium hydroxide.
→ Substances which are neither acidic nor basic are called neutral.
→ Indicators are used to test the nature of substances.
→ Turmeric, hibiscus, litmus, red cabbage, are some Natural indicators. 4* In neutralization reaction water and salt will be formed.
→ Acid + base → water + salt
→ Acids are used to make in batteries, fertilizers.
→ Acids are used in preservation of food eg: vinegar.
→ Bases are used in making soaps and cleaning substances.
→ Soap will be prepared by adding fatty acids to alkalies.
→ pH scale is used to test for the strength of acids and bases.
→ Acid : Acids are sour in taste. The word acid came from the Latin word ‘acere’ means sour.
Ex: lemon juice
→ Base : Bases are bitter in taste and slippery to touch.
Ex: Soap, tooth paste.
→ Neutral substance : The substance which is neither an acid nor a base is known as neutral substance.
Ex: Pure water, salt solution, sugar solution etc.
→ Indicators : Substances which are used to test acids or bases are called acid base indicators.
→ Natural indicators : Indicators obtained from natural sources are called as Natural indicators.
Ex: turmeric, hibiscus
→ Synthetic indicators : An indicator prepared from artificial sources is known as Synthetic indicator.
Ex: methyl orange, phenolphthalein.
→ Olfactory indicator : Substances which change their smell when mixed with acid or base are known as olfactory indicators.
Ex: onion, vanilla and clove oil
→ Universal indicator : It is a mixture of different indicators. It shows different colours in different solutions.
→ Litmus : It is the commonly used indicator in the laboratory. It is available in red and blue colours. Blue litmus turns red in acids. Red litmus turns blue in bases.
→ pH scale : Strength of acid or base solution is measured in pH scale. This scale was introduced by Sorensen. The range of pH scale is from 0 to 14.
→ Neutralization reaction : Reaction of an acid and a base is called neutralization re-action. The substances formed in neutralization reaction are water and salt.
→ Salt : Salts are formed by neutralization reaction. They are chemically neutral.
Ex: Common salt.
→ Soap : Soap is a salt with basic nature. It is prepared by adding fatty acids like coconut oils to alkalis like Sodium hydrox-ide or Potassium hydroxide.
→ Antacids : Antacids contain bases, eg: aluminum hydroxide, milk of magnesia. The bases in the antacids neutralize gastric juice and give us relief.
→ Acid rain : Rain water with slight acidic nature is called Acid rain. Air pollution is a major cause of acid rains. Acid rain can cause damage to buildings, historical monuments like Taj mahal, plants and animals
