In the electrolysis of aqueous sodium chloride solution which of the half-cell reaction will occur at anode?

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Na+(aq)+e−⟶Na(s);Ecell∘=−2.71V

2H2O(l)⟶O2(g)+4H+(aq)+4e−;Ecell∘−1.23V

H+(aq)+e−⟶12H2(g);Ecell∘=0.00V

Cl−(aq)⟶12Cl2(g)+e−;Ecell ∘=1.36V

answer is D.

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Detailed Solution

In case of electrolysis of aq .NaCl oxidation reaction occurs at anode as follows: Cl−(aq)⟶12Cl2(g)+e−;E∘=1⋅36V2H2O(l)⟶O2(g)+4H+(aq)+4e−⋯; Ecell∘=1.23VBut due to lower Ecello value, water should get oxidised in preference of Cl- (aq)However, the actual reaction taking place is the first one i.e. Cl2 is produced.This unexpected result is explained on the basis of the concept of 'over voltage', i.e. water needs greater voltage for oxidation to O2 (as it is kinetically slow process) than that needed for oxidation of Cl- ions to Cl2.

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