Chapter 2 — Acids, Bases and Salts

Chapter 2 of the Class 10 Science NCERT textbook, "Acids, Bases and Salts", covers their chemical properties, the pH scale (0–14), neutralisation reactions, and important salts like baking soda, washing soda, bleaching powder, and Plaster of Paris derived from common salt.

• What makes acids and bases behave differently — Acids release H⁺ ions in water and turn blue litmus red, while bases release OH⁻ ions and turn red litmus blue. This ionic difference underlies their reactions with metals, carbonates, and each other in neutralisation.
• The pH scale and why it matters — The pH scale from 0 to 14 measures how acidic or basic a solution is, with 7 as neutral. This single idea explains everyday phenomena such as digestion, tooth decay below pH 5.5, and the damage caused by acid rain.
• Useful salts made from common salt — Sodium chloride is the raw material for many industrially important salts. From it we obtain sodium hydroxide, bleaching powder, baking soda, washing soda, and Plaster of Paris — each with distinct household and industrial uses.

1. 01Acids turn blue litmus red and produce H⁺(aq) ions in water; bases turn red litmus blue and produce OH⁻(aq) ions in water.
2. 02Acid + Metal → Salt + Hydrogen gas; Metal carbonate + Acid → Salt + Carbon dioxide + Water.
3. 03Neutralisation reaction: Acid + Base → Salt + Water; e.g., NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l).
4. 04The pH scale (0–14) measures hydrogen ion concentration: pH 7 is neutral, below 7 is acidic, above 7 is basic. Human body functions within pH 7.0–7.8.
5. 05Tooth decay begins when mouth pH drops below 5.5; toothpastes are basic to neutralise excess acid. Acid rain has pH less than 5.6.
6. 06Common salt (NaCl) is the raw material for NaOH (chlor-alkali process), bleaching powder Ca(ClO)₂, baking soda NaHCO₃, and washing soda Na₂CO₃·10H₂O.