question_answer 50)

  In the electrolysis of aqueous sodium chloride solution which of the half-cell reaction will occur at anode? (a) (b)   (c) (d)

Answer:

                  (d) In case of electrolysis of aqueous NaCI oxidation reaction occurs at anode as follows But due to lower  value water should get oxidised in preference of Cl- (aq). However, the actual reaction taking place in the concentrated solution of NaCI is (d) and not (b) i.e., Cl2 is produced and not O2. This unexpected result is explained on the basis of the concept of 'overvoltage', 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. Thus, the correct option is (d) not (b).