JEE Main · 2022 · 24 Jun 2022 · Shift 2 · s-Block Elements

Sodium hydroxide (NaOH) is industrially produced by the electrolysis of aqueous sodium chloride (brine) in the Castner-Kellner cell. During this process:

At cathode: ${\mathrm{Na}}^{+}+{\mathrm{e}}^{-}\stackrel{\mathrm{Hg}}{\to }\mathrm{Na}$-amalgam

At anode: ${\mathrm{Cl}}^{-}\to \frac{1}{2}{\mathrm{Cl}}_2+{\mathrm{e}}^{-}$

The Na-amalgam is then treated with water:
$2\mathrm{Na}(\text{amalgam})+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{NaOH}+{\mathrm{H}}_2+2\mathrm{Hg}$

Thus, hydrogen gas is obtained as a byproduct.