Acids Bases and Salts NCERT Exemplar Problems

Short Answer Questions

Part 1

Question 31: Match the acids given in Column (A) with their correct source given

Column A	Column B
(a) Lactic acid	(1) Tomato
(b) Acetic acid	(2) Lemon
(c) Citric acid	(3) Vinegar
(d) Oxalic acid	(4) Curd

Answer: (a) 4, (b) 3, (c) 2, (d) 1

Question 32: Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)

Column A	Column B
(a) Plaster of Paris	(1) Ca(OH)₂
(b) Gypsum	(2) CaOCl₂
(c) Bleaching powder	(3) CaSO₄.2H₂O
(d) Slaked lime	(4) CaSO₄.0.5H₂O

Answer: (a) 4, (b) 3, (c) 2, (d) 1

Question 33: What will be the action of the following substances on litmus paper? (Dry HCl gas, Moistened NH₃ gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.)

Answer:

Dry HCl – No action
Moistened NH₃ gas – Turns red litmus to blue
Lemon Juice – Turns blue litmus to red
Carbonated soft drink – Turns blue litmus to red.
Curd – Turns blue litmus to red
Soap solution – Turns red litmus to blue.

Explanation:

Dry HCl does not liberate hydrogen ion, hence no action takes place with litmus paper.
NH₃ gas forms ammonium hydroxide in with water which turns red litmus paper blue.
Lemon juice is citric acid, so it turns blue litmus paper red.
Carbonate soft drink contains carbon dioxide dissolved in water. Carbon dioxide forms carbonic acid; with water; which turns blue litmus paper red.
Curd contains lactic acid and hence turns blue litmus paper to red.
Soap solution is basic in nature hence it turns red litmus paper to blue.

Question 34: Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.

Answer: Name of acid present in ant sting: Methanoic acid

Chemical Formula of methanoic acid: HCOOH

Method to get relief from the discomfort caused by the ant sting: Rubbing baking soda over the location of ant sting.

Explanation: Since baking soda is a base thus by rubbing over the ant sting it neutralizes the methanoic acid present in ant sting and gives relief from pain.

Question 35: What happens when nitric acid is added to egg shell?

Answer: Egg shell is made of calcium carbonate. We know that when calcium carbonate reacts with nitric acid, it gives carbon dioxide, calcium nitrate and water. Same reaction happens when nitric acid is poured over egg shell.

CaCO₃ + 2HNO₃ ⇨ Ca(NO₃ )₂ + CO₂ + H₂O

Question 36: A student prepared solutions of (i) an acid and (ii) a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?

Answer: While answering this question, we need to make certain assumptions. Let us assume that laboratory has all the necessary items but litmus paper. We can use phenolphthalein to check which of the beakers contains acid and which one contains a base. Apart from that, we can also use other natural indicators; like China rose or turmeric.