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Class 10 Science: Acids, Bases and Salts, 8 practice questions with answers

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These are 8 practice questions on NCERT Class 10 Science Chapter 2, Acids, Bases and Salts, each with a short answer and the textbook page it comes from. They cover the pH scale, what acids do to metals and carbonates, neutralisation, safe dilution, the salts plaster of Paris and washing soda, and a short calculation. Try each one before you read the answer.

These questions are our own, drafted with AI help. Every number was re-computed by a test script and every statement was checked against the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

The pH scale and neutralisation

Question 1. Four solutions show pH values of 2, 7, 8 and 13 on universal indicator paper. Which pH belongs to the most strongly alkaline solution?

Answer: pH 13. The pH of a neutral solution is 7; values below 7 are acidic, and as the pH rises from 7 to 14 the strength of the alkali increases. So pH 2 is strongly acidic, pH 7 neutral, pH 8 weakly basic and pH 13 the most strongly alkaline. (Section 2.3, page 25.)

Question 2. What is the reaction between an acid and a base called, and what does it produce?

Answer: a neutralisation reaction, which gives a salt and water. In general: base + acid → salt + water. For example NaOH + HCl → NaCl + H₂O. (Section 2.1.4, page 21.)

Reactions of acids

Question 3. Zinc granules are added to dilute hydrochloric acid. Which gas is evolved?

Answer: hydrogen. When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed (here, zinc chloride). (Chapter summary, page 33; the reaction of acids with metals is in section 2.1.2.)

Question 4. Dilute hydrochloric acid is added to sodium carbonate. Which products are formed? (Sodium chloride and hydrogen gas; sodium hydroxide and chlorine gas; or sodium chloride, carbon dioxide and water.)

Answer: sodium chloride, carbon dioxide and water. Metal carbonate + acid → salt + carbon dioxide + water: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂. The carbon dioxide turns lime water milky, a white precipitate of calcium carbonate. (Section 2.1.3, Activity 2.5, page 20.)

Question 5. What is the safe way to dilute concentrated sulphuric acid? (Pour water slowly into the acid without stirring; add the acid slowly to water with constant stirring; or pour water quickly into the acid.)

Answer: add the acid slowly to water with constant stirring. Dissolving an acid or a base in water is a highly exothermic process. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. (Page 24.)

Salts

Question 6. A salt is formed from a strong acid and a weak base. What is the pH of its solution in water? (Exactly 7, more than 7, or less than 7.)

Answer: less than 7. Salts of a strong acid and a strong base are neutral (pH 7); salts of a strong acid and a weak base are acidic (pH less than 7); salts of a strong base and a weak acid are basic (pH more than 7). (Section 2.4, page 29.)

Question 7. Gypsum, CaSO₄·2H₂O, is heated at 373 K to form plaster of Paris, CaSO₄·½H₂O. How many molecules of water of crystallisation are lost per formula unit of gypsum?

Answer: 1½ molecules. Gypsum has two water molecules per formula unit and plaster of Paris has ½, so 2 − ½ = 1½ are lost. (Section 2.4.4, page 32: heating gypsum at 373 K gives calcium sulphate hemihydrate, called plaster of Paris.)

Question 8. Washing soda is Na₂CO₃·10H₂O (Na = 23, C = 12, O = 16, H = 1). (a) What is its formula mass? (b) What percentage of it is water of crystallisation, to one decimal place? (c) 572 g of washing soda is heated until all its water of crystallisation is driven off. How many grams of water are lost?

Answer: (a) Sodium carbonate Na₂CO₃ is 46 + 12 + 48 = 106 u, and ten water molecules add 10 × 18 = 180 u, so the formula mass is 286 u. (b) 180 ÷ 286 × 100 ≈ 62.9%. (c) 572 g is 2 × 286 g, so the water lost is 2 × 180 = 360 g. (The formula Na₂CO₃·10H₂O for washing soda is on page 31; the calculation is ours.)

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Sources

All opened and read on 21 October 2026. Page numbers are the printed page numbers of the textbook.

The definitions and facts are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.