Question

Acidified water is electrolysed using platinum electrodes. What is the volume ratio of hydrogen to oxygen?

Answer 1

Electrolysis is the decomposition of compound by passing electric current in its aqueous or molten state.

1. Pure water do not electrolysed because it contains water molecules which do not dissociate into ions.

2. By adding acid such as sulphuric acid ${\mathrm{H}}_2{\mathrm{SO}}_4$ in water. It helps in ionization of water.

Chemical Equation : This acidified water dissociates into ions. ${\mathrm{H}}^{+},{\mathrm{OH}}^{-},{\mathrm{SO}}_4^{2-}$ ions are present in the solution.

$$\begin{gathered} {\mathrm{H}}_2{\mathrm{SO}}_4\rightleftharpoons 2{\mathrm{H}}^{+}+{\mathrm{SO}}_4^{2-} \\ \mathrm{sulphuric}\mathrm{hydrogen}\mathrm{sulphate} \\ \mathrm{acid}\mathrm{ion}\mathrm{ion} \end{gathered}$$

$$\begin{gathered} {\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}^{+}+{\mathrm{OH}}^{-} \\ \mathrm{water}\mathrm{hydroxide}\mathrm{ion} \end{gathered}$$

The electrolysis of acidified water gives two hydrogen molecules and one oxygen molecule.

Electrolysis of acidified water :

$2{\mathrm{H}}_2\mathrm{O}\rightleftharpoons 2{\mathrm{H}}_2+{\mathrm{O}}_2$

Hence, volume ratio of hydrogen to oxygen is $2:1$.