Chapter 2: Acids, Bases and Salts

This chapter covers properties of acids and bases, the pH scale, neutralisation reactions, and common salts.

Q1. A solution turns red litmus blue. Its pH is likely to be:
(a) 1 (b) 4 (c) 7 (d) 10

Solution

Answer: (d) 10

A solution that turns red litmus blue is basic (alkaline) in nature. Basic solutions have pH greater than 7.

• pH = 1 → Strongly acidic

• pH = 4 → Weakly acidic

• pH = 7 → Neutral

• pH = 10 → Basic ✓

Q2. What happens when dilute HCl is added to zinc granules?

Solution

When dilute hydrochloric acid (HCl) is added to zinc granules:

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) ↑

• Zinc reacts with dilute HCl to form zinc chloride and hydrogen gas.

• This is a displacement reaction where zinc displaces hydrogen from the acid.

• Bubbles of hydrogen gas are observed on the surface of zinc granules.

• The reaction is exothermic (releases heat).

pH Scale showing acidic, neutral and basic ranges with common examples

Key Concepts:
• Acids taste sour, turn blue litmus red, pH < 7
• Bases taste bitter, turn red litmus blue, pH > 7
• Neutralisation: Acid + Base → Salt + Water
• Strong acid: HCl, HNO₃, H₂SO₄ | Weak acid: CH₃COOH, H₂CO₃
• Indicators: Litmus, Phenolphthalein, Methyl orange

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