Question

(a) To carry out the so-called "electrolysis of water", sulphuric acid is added to water.
How does the addition of sulphuric acid produce a conducting solution?
(b) Copy and complete the following sentence:
With platinum electrodes, hydrogen is liberated at the ________ and oxygen at the ________ during the electrolysis of acidified water.

Answer 1

(a) Pure water contains only molecules and lacks ions; it cannot ionise and hence, cannot conduct electricity. But when sulphuric acid is added to it, ions from the acid are introduced into pure water. Then the degree of ionisation in the acidulated water increases and due to this, water conducts electricity.
The dissociation of acidified water will be:
${\mathrm{H}}_2{\mathrm{SO}}_4$⇌ $2{\mathrm{H}}^{+}+{\mathrm{SO}}_4^{2-}$
${\mathrm{H}}_2\mathrm{O}$⇌${\mathrm{H}}^{+}+{\mathrm{OH}}^{-}$
Thus, the presence of ions is vital for electrolysis reaction to occur and therefore, the addition of acid is necessary before proceeding with the electrolysis of 'water'.
(b) With platinum electrodes, hydrogen liberated at cathode and oxygen at the anode during the electrolysis of acidified water.