Value of standard electrode potential for the oxidation of `Cl^(-)` ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why is `Cl^(-)` oxidsied at anode instead of water?

Explanation

The oxidation reactions taking place at anode are :
`2Cl^(-)(aq)toCl_(2)(g)+2e^(-) ,E_(("oxid"))^(@)=-1.23" V"`
`2Cl^(-)(aq)toCl_(2)(g)+2e^(-) ,E_(("oxid"))^(@)=-1.23" V"`
Due to the overvoltage of oxygen `(O_(2))`, its liberation is kinetically slower than that of `Cl^(-)` ions. Therefore, `Cl^(-)` ions are oxidised to `Cl_(2)` gas. For more details, consult section 3.15 (Text part).