Question

Discuss the electrolysis mechanism by taking the example of fused sodium chloride.

Answer 1

Molten sodium chloride produces chlorine at the anode and deposits sodium at the cathode when an electric current flows through it. Here’s an explanation for this.

In the molten state, sodium chloride ionises as

\[\ce{NaCl (molten) <=> Na+ + Cl-}\]

Na⁺ ions flow towards the cathode and Cl⁻ ions towards the anode when an electric current flows. Every Cl⁻ ion contributes an electron to the anode and is oxidised into a Cl atom, while every Na⁺ ion removes an electron from the cathode and is reduced into a Na atom. Cl atoms combine to produce Cl₂ molecules because they are unable to exist separately. The following is an expression for the reactions.

At cathode (reduction): \[\ce{Na+ + e- -> Na}\]

At anode (oxidation): \[\ce{Cl- - e- -> Cl}\] (Primary charge)

\[\ce{Cl + Cl -> Cl2_{(g)}}\] (Secondary charge)

Therefore, sodium is produced at the cathode, and chlorine gas is produced at the anode due to the electrolysis of fused sodium chloride.