These DAV Class 7 Science Notes and DAV Class 7 Science Chapter 4 Notes – Acids, Bases and Salts act as excellent revision resources, particularly in preparation for board exams.
Acids, Bases and Salts Class 7 DAV Notes
→ Acid: An acid is a substance which is sour in taste.
→ Base: A base is a substance which is bitter in taste.
→ Mineral Acids: Acids which are prepared from minerals are called mineral acids. Examples: Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3), Sulphurous acid (H2SO4), Phosphoric acid (H3PO4). Mineral acids are strong acids.
→ Alkalis: Some bases are soluble in water. They are called alkalis. For example: sodium hydroxide and aluminium hydroxide are bases, but sodium hydroxide is an alkali. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are strong bases. Ammonium hydroxide (NH4OH) and aluminium hydroxide [AI(OH)3] are weak bases.
→ Indicators
An indicator is a substance which shows different colours; in an acidic and a basic medium. Indicators help in identifying acids and bases.
→ Litmus: Litmus solution is prepared from lichen. Litmus paper is made from litmus solution. A blue litmus paper turns red in acidic solution. A red litmus paper turns blue in alkaline solution.
→ Turmeric: Turmeric is also used as an indicator. Turmeric turns red in basic solution and remains yellow in acidic solution.
→ Phenolphthalein: Phenolphthalein is a synthetic indicator. It remains colourless in acidic solution and turns pink in basic solution.
→ Neutralisation and Formation of Salts
The reaction between an acid and a base is called neutralisation reaction. Salt and water are formed after neutralisation reaction. Some examples of neutralisation reaction are given below.
Naming of Saits:
→ Salts of sulphuric acid (H2SO4) are named as sulphate.
→ Salts of hydrochloric acid (HCl) are named as chlorides.
→ Salts of nitric acid (HNO3) are named as nitrates.
→ Salts of sulphurous acid (H2SO3) are named as sulphites.
→ Salts of carbonic acid (H2CO3) are named as carbonates.
→ Salts of acetic acid (CH3COOH) are named as acetates.
Properties of Salts:
→ Salts are formed after neutralisation reaction.
→ Most of the salts are readily soluble in water.
→ Salts are bad conductors of electricity in their solid state. Molten salts and solution of salt in water are good conductors of electricity.
Classification of Salts:
→ Neutral Salts: When a salt is formed after the reaction between a strong acid and a strong base, it is called a neutral salt. The aqueous solution of a neutral salt is neutral, i.e. it shows neither acidic nor basic property. Sodium chloride (NaCl), Potassium chloride (KCl), Potassium nitrate (KNO3), Sodium sulphate (Na2SO4), etc. are examples of neutral salt.
→ Acidic Salt: When a salt is formed after the reaction between a strong acid and a weak base, it is called an acidic salt. The aqueous solution of an acidic salt is acidic. Aluminium chloride (AlCl3), Ammonium nitrate (NH4NO3), Zinc sulphate (ZnSO4) and Copper chloride (CuCI2) are examples of acidic salt.
→ Basic Salt: When a salt is formed after the reaction between a weak acid and a strong base, it is called a basic salt. The aqueous solution of a basic salt is basic. Sodium acetate (CH3COONa), Sodium formate (HCOONa) and Sodium carbonate (Na2CO3) are examples of basic salt.
→ Acid: A chemical which tastes sour.
→ Dilute acid: When concentration of acid is low, it is called dilute acid.
→ Base: A chemical which tastes bitter and turns red litmus blue.
→Alkali: A bases which is soluble in water.
→ Mineral acid: Acid made from minerals present in earth.
→ Organic acid: Acid obtained from plants and animals.
→Indicator: A substance which shows change in colour in acidic or basic medium.
→ Neutralisation reaction: A reaction between an acid and a base which results in formation of a salt and water.
→ Organic Acids: Acids which are naturally occurring and are found in plants and animals are called organic acids. Examples: Formic acid (HCOOH), Acetic acid (CH3COOH). Organic acids are weak acids.
| Food | Acid present |
| Guava | Oxalic acid |
| Lemon, orange | Citric acid |
| Tamarind, gooseberry | Tartaric acid |
| Vinegar | Acetic acid |