When a solution of sodium sulfate, Na2SO4, adjusted to a pH of 7 is electrolyzed

Question

When a solution of sodium sulfate, Na2SO4, adjusted to a pH of 7 is electrolyzed, red litmus and a gas is evolved in the anodic chamber. In the cathodic chamber, red litmus turns blue and a gas is also evolved. Write the balanced equations for the half-reaction occurring at the anode and the cathode.

Explanation / Answer

Two reactions can take place at the cathode. 2 H2O (l) + 2 e - ---> H2 (g) + 2 OH- (aq) E° = -0.8277 V Na + (aq) + e - ---> Na (s) E° = -2.7109 V Two reactions can also occur at the anode. 2 SO4 2- (aq) ---> S2O8 (aq) + 2 e - E° = -2.05 V 2 H2O (l) ---> O2(g) + 4 H+ (aq) + 4 e - E° = -1.229 V s2o8 is acidic so red turns blue

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