Question

Assertion (A): In the electrolysis of acidified water, the volume of hydrogen liberated is twice the volume of oxygen formed.
Reason (R): Water has hydrogen and oxygen in the ratio of 1:2 by volume.

• A. (A) is true but (R) is false.
• B. (A) is false but (R) is true.
• C. Both (A) and (R) are true and (R) is the correct explanation of (A).
• D. Both (A) and (R) are true, but (R) is not the correct explanation of (A).

Hint:

In a Hoffmann voltameter, the level of water in the cathode limb (where H_2 collects) will be twice as low as the level in the anode limb (where O_2 collects)!

Answer 1

The Correct Option is A

To determine the correctness of the assertion and the reason, we need to evaluate both statements:

• Assertion (A): In the electrolysis of acidified water, the volume of hydrogen liberated is twice the volume of oxygen formed.

During the electrolysis of water, the following reaction takes place:

\(2H_2O(l) \rightarrow 2H_2(g) + O_2(g)\)

This indicates that 2 moles of water decompose to produce 2 moles of hydrogen gas and 1 mole of oxygen gas. By Avogadro's law, under constant conditions of temperature and pressure, equal moles of gases occupy equal volumes. Therefore, the volume of hydrogen produced is indeed twice that of oxygen. Thus, the assertion is true.

• Reason (R): Water has hydrogen and oxygen in the ratio of 1:2 by volume.

The chemical formula of water is \(H_2O\), indicating that each molecule of water contains 2 hydrogen atoms and 1 oxygen atom. However, this is a molecular ratio, not a volume ratio. In terms of the volume ratio from water's composition, the volume of hydrogen in water is twice that of oxygen, not the other way around. Therefore, the reason is false.

Based on this analysis:

• (A) is true but (R) is false.