Question

Value of standard electrode potential for the oxidation of $C{l}^{-}$ ions is more positive than that of water, even then the electrolysis of aqueous sodium chloride, why is $C{l}^{-}$ oxidised at anode instead of water?

Answer 1

In the electrolysis
At anode, oxidation reaction takes place and ions get oxidized.
At cathode, reduction reaction takes place and ions get reduced.
Thus, reaction at anode will be:

$C{l}^{-}\to \frac{1}{2}C{l}_2+e^{-}{E}^0=1.36V$
$2H_{2}O\to O_2+4H^{-}+4e^{-}{E}^0=1.23V$

At anode, the reaction with lower value of $E^0$ is preferred for oxidation. Thus, at anode $O_2$(g) must have been produced instead of $C{l}_2$(g) but the formation of $O_2$ at anode is kinetically so slow and needs some overvoltage to be additionally provided.

Thus, In electrolysis of aqueous sodium chloride solution $C{l}^{-}$ is oxidised at anode.