Acids Bases and Salts

NCERT Exemplar Problems

MCQs Part 3

Question 21: Which of the following is used for dissolution of gold?

1. Hydrochloric acid
2. Sulphuric acid
3. Nitric acid
4. Aqua regia
   Answer: (d) Aqua regia

Explanation: Gold is an inert metal and does not react with any acid. Aqua regia is a mixture of nitric acid and hydrochloric acid in 1 : 3 ratio. It is used by goldsmiths to clean ornaments.

Question 22: Which of the following is not a mineral acid?

1. Hydrochloric acid
2. Citric acid
3. Sulphuric acid
4. Nitric acid
   Answer: (b) Citric acid

Explanation: It is an organic acid.

Question 23: Which among the following is not a base?

1. NaOH
2. KOH
3. NH₄OH
4. C₂H₅OH
   Answer: (d) C₂H₅OH

Explanation: It is ethanol, an organic compound.

Question 24: Which of the following statements is not correct?

1. All metal carbonates react with acid to give a salt, water and carbon dioxide
2. All metal oxides react with water to give salt and acid
3. Some metals react with acids to give salt and hydrogen
4. Some non metal oxides react with water to form an acid
   Answer: (b) All metal oxides react with water to give salt and acid.

Explanation: Oxides of metals are basic in nature, so they cannot give acid or salt on dissolution in water.

Question 25: Match the chemical substances given in Column (A) with their appropriate application given in

1. A—(ii), B—(i), C—(iv), D—(iii)
2. A—(iii), B—(ii), C—(iv), D—(i)
3. A—(iii), B—(iv), C—(i), D—(ii)
4. A—(ii), B—(iv), C—(i), D—(iii)
   Answer: (c) A – (iii), B – (iv), C – (i), D – (ii)

Explanation: Bleaching powder is used as bleaching agent. So, we can easily rule out option d. Baking soda is used as an antacid. So, we can zero in on option c.

Question 26: Equal volumes of hydrochloric acid and sodium hydroxide solutions of same concentration are mixed and the pH of the resulting solution is checked with a pH paper. What would be the colour obtained?

1. Red
2. Yellow
3. Yellowish green
4. Blue
   Answer: (c) Yellowish green

Explanation: This is the colour of pH paper in neutral solution. Reaction between hydrochloric acid and sodium hydroxide will result in neutralization.

Question 27: Which of the following is(are) true when HCl (g) is passed through water?

1. It does not ionise in the solution as it is a covalent compound.
2. It ionises in the solution
3. It gives both hydrogen and hydroxyl ion in the solution
4. It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule

1. (i) only
2. (iii) only
3. (ii) and (iv)
4. (iii) and (iv)
   Answer: (c) (ii) and (iv)

Explanation: Acid breaks into ions in aqueous solution and gives hydronium ion (H₃O⁺)

Question 28: Which of the following statements is true for acids?

1. Bitter and change red litmus to blue
2. Sour and change red litmus to blue
3. Sour and change blue litmus to red
4. Bitter and change blue litmus to red
   Answer: (c) Sour and change blue litmus to red

Question 29: Which of the following are present in a dilute aqueous solution of hydrochloric acid?

1. H₃O⁺ + Cl⁻
2. H₃O⁺ + OH⁻
3. Cl⁻ + OH⁻
4. un-ionised HCl
   Answer: (a) H₃O⁺ + Cl⁻

Explanation: Same as in previous question.

Question 30: Identify the correct representation of reaction occurring during chloralkali process

1. 2NaCl(l) + 2H₂O(l) ⇨ 2NaOH(l) + Cl₂(g) + H₂(g)
2. 2NaCl(aq) + 2H₂O(aq) ⇨ 2NaOH(aq) + Cl₂(g) + H₂(g)
3. 2NaCl(aq) + 2H₂O(l) ⇨ 2NaOH(aq) + Cl₂(aq) + H₂(aq)
4. 2NaCl (aq) + 2H₂O (l) ⇨ 2NaOH (aq) + Cl₂(g) + H₂(g)
   Answer: (d) 2NaCl (aq) + 2H₂O (l) ⇨ 2NaOH (aq) + Cl₂(g) + H₂(g)

Explanation: Brine (aqueous solution of common salt) is used in chloralkali process. Chlorine and hydrogen gases are evolved and sodium hydroxide is formed in aqueous solution.