Predict half reactions of electrolysis of MgCl2

Question

List the anode and cathode half-reactions that might occur when an aqueous solution of MgCl2 is electrolyzed in a cell having inert electrodes. Predict which half-reactions will occur, and justify the answer.

Answer 1

Since the question states that you are using an aqueous solution of MgCl2, you will have present, H₂O, H⁺, Mg²⁺ and Cl^-

Anode: 2Cl^- ==> Cl₂ + 2e- + H2O ==> ClO^- + 2H⁺ + Cl^- (will occur)

Cathode: 2H⁺ + 2e- ==> H₂ (will occur)

Cathode: Mg²⁺ + 2e- ==> Mg (will not occur)

The deposition of solid Mg will not occur because in aqueous solution, H⁺ will be reduced before Mg²⁺ (see reduction potentials for H⁺ vs. Mg²⁺)