Question

Discuss the electrolysis of an aqueous solution of sodium chloride and explain the products formed at the two electrodes.

Answer 1

During the electrolysis of an aqueous solution of sodium chloride, the reactions occurring are as follows:

At the cathode, hydrogen ions (from water) are preferred over sodium ions because they possess a lower discharge potential.

Reaction at cathode:

\[\ce{2H2O_{(l)} + 2e- -> H2_{(g)} + 2OH^-_{ (aq)}}\]

At the anode, chloride ions are preferred over hydroxide ions due to their higher concentration and overvoltage for oxygen.

Reaction at the anode:

\[\ce{2Cl^-_{ (aq)} -> Cl2_{(g)} + 2e-}\]

Net cell reaction:

\[\ce{2Cl^-_{ (aq)} + 2H2O_{(l)} -> Cl2_{(g)} + H2_{(g)} + 2OH^-_{ (aq)}}\]

Chloride ions are discharged at the positive electrode (anode) as chlorine gas, and hydrogen gas is liberated at the negative electrode (cathode). Sodium ions and hydroxide ions remain in the solution, forming sodium hydroxide (NaOH).