Question

Give reasons:

On the basis of E° values, O₂ gas should be liberated at anode but it is Cl₂ gas which is liberated in the electrolysis of aqueous NaCl.

Account for the following:

On the basis of E° values, O₂ gas should be liberated at anode but it is Cl₂ gas which is liberated in the electrolysis of aqueous NaCl.

Answer 1

While Cl₂ gas is released during the electrolysis of aqueous NaCl, O₂ gas should be released at the anode based on Eº values. It results from the over-voltage phenomenon. It has been found through experimentation that the voltage needed for electrolysis is higher than what is determined using standard potentials. We refer to this necessary additional voltage as over-voltage. It is necessary because both half reactions have a slow rate of electron transport at the electrode-solution contact. The amount of overvoltage needed to produce oxygen is far more than that needed to form chlorine.