Following two reactions can occur at cathode in the electrolysis of aqueous sodium chloride:
Na+ + e– → Na(s) 2H2O(l) + 2r → H2(g) + 2OH–(aq)
E°red = – 0.83 V
Which reaction takes place preferentially and why?
We know from electrochemical series and the standard reduction electrode potential that higher the reduction potential of a species, there is increasing tendency for its reduction to occur. Here, the standard reduction potential of water is greater than that of sodium ion, so reduction of water takes place in preference to that of sodium ion and H2 is liberated at cathode.