Acid, Bases and Salts - Class - 7th CBSE Notes

Acids and Bases

1. Acids: Acids are substances that have a sour taste and turn blue litmus paper red. Examples include lemon juice and vinegar.
2. Bases: Bases have a bitter taste and slippery texture. They turn red litmus paper blue. Examples include soap and baking soda.

Natural Indicators

Natural indicators like litmus paper, turmeric, and China rose are used to detect whether a substance is acidic or basic.

Types of Acids

Acids can be classified into two types:

1. Organic Acids: Acids derived from plants and animals (e.g., citric acid, lactic acid).
2. Mineral Acids: Strong acids obtained from minerals (e.g., hydrochloric acid, sulfuric acid).

Properties of Acids

1. Sour in taste
2. Turn blue litmus paper red
3. React with metals to produce hydrogen gas

Uses of Acids

1. Nitric Acid (HNO₃): Used in fertilizers and explosives.
2. Sulfuric Acid (H₂SO₄): Used in batteries and manufacturing chemicals.
3. Hydrochloric Acid (HCl): Used in cleaning and digestion in the stomach.
4. Acetic Acid (CH₃COOH): Found in vinegar, used in food preservation.

Types of Bases

Bases can also be classified into strong and weak bases:

1. Strong Bases: Bases that completely dissociate in water (e.g., sodium hydroxide).
2. Weak Bases: Bases that partially dissociate in water (e.g., ammonium hydroxide).

Properties of Bases

1. Bitter in taste
2. Turn red litmus paper blue
3. Slippery to touch

Uses of Bases

1. Calcium Hydroxide: Used in whitewashing buildings.
2. Magnesium Hydroxide: Used as an antacid to neutralize stomach acid.
3. Sodium Hydroxide (NaOH): Used in soap-making.
4. Ammonium Hydroxide: Used in household cleaners.

Neutralisation

Neutralisation is the reaction between an acid and a base to form salt and water. This reaction helps balance pH levels in various situations.

Neutralisation in Our Daily Life

1. Use of Antacids: Antacids neutralize excess stomach acid and provide relief from indigestion.
2. Soil Treatment: Acidity in soil can be reduced using slaked lime (calcium hydroxide).
3. Waste Treatment: Industrial waste containing acids is treated with bases before disposal to neutralize harmful effects.
4. Stings of Ants: Ant stings inject formic acid, which can be neutralized using a mild base like baking soda.

Salt

Salt is formed by the neutralization reaction between an acid and a base. Common salt (NaCl) is used in food, while other salts are used in various industries.

Properties of Salts

1. Salts have a neutral pH (neither acidic nor basic).
2. They dissolve in water to form ions.
3. Many salts are crystalline in nature.

Uses of Salts

1. Common salt (NaCl) is used in cooking.
2. Salts are used in fertilizers (e.g., ammonium nitrate).
3. Salts are used in manufacturing chemicals (e.g., sodium carbonate).

Neutralization Reaction Diagram