NCERT Class X Science Class: Chapter – 2. Acids, Bases and Salts – Part-8 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Question 41:

What are strong and weak acids? In the following list of acids, separate strong acids from weak acids. Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.


In aqueous solutions strong acids ionize completely and provide hydronium ions. On the other hand weak acids are partially ionized and an aqueous solution of same molar concentration provides a much smaller concentration of ions.

Strong acids Hydrochloric acid, sulphuric acid, nitric acid

Weak acid Citric acid, acetic acid, formic acid

Question 42:

When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilized in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.


When zinc reacts with dilute solution of strong acid, it forms salt and hydrogen gas is evolved.

When a burning splinter is brought near the mouth of the test tube, the gas burns with a pop sound.

Long Answer Questions

Question 43:

In the following schematic diagram for the preparation of hydrogen gas as shown in Figure, what would happen if following changes are made?

Image the Experment of Hydrogen Gas
  1. In place of zinc granules, same amount of zinc dust is taken in the test tube
  2. Instead of dilute sulphuric acid, dilute hydrochloric acid is taken
  3. In place of zinc, copper turnings are taken
  4. Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.



  1. Hydrogen gas will evolve with greater speed
  2. Almost same amount of gas is evolved
  3. Hydrogen gas is not evolved
  4. If sodium hydroxide is taken, hydrogen gas will be evolved