Question

Explain the mechanism of electrolysis by taking a suitable example.

Answer 1

The process of electrolysis can be explained on the basis of the theory of ionisation. 

When an electric current is passed through molten sodium chloride, sodium is deposited at the cathode and chlorine is liberated at the anode. This can be explained as follows.

In the molten state, sodium chloride ionises as

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

On passing an electric current, Na⁺ ions move towards the cathode while Cl⁻ ions move towards the anode. Each Na⁺ ion takes an electron from the cathode and gets reduced into an Na atom, whereas each Cl⁻ ion gives an electron to the anode and gets oxidised into a Cl atom. Since Cl atoms cannot exist independently, they combine to form Cl₂ molecules. The reactions can be expressed as given below.

At cathode:

\[\ce{Na+ + e- -> Na}\] (Reduction)

At anode:

\[\ce{Cl- - e- -> Cl}\] (Oxidation primary change)

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

Hence, on account of the electrolysis of fused sodium chloride, sodium is obtained at the cathode while chlorine gas is at the anode.