Question

On the basis of \( E^\circ \) values, O\(_2\) gas should be liberated at the anode, but it is Cl\(_2\) gas that is liberated in the electrolysis of aqueous NaCl.

Hint:

Even though oxygen has a more positive reduction potential, chlorine is preferentially produced at the anode due to the high concentration of chloride ions.

Answer 1

The standard electrode potential for the reduction of oxygen to water is \( E^\circ_{\text{O}_2/\text{H}_2\text{O}} = +1.23 \, \text{V} \), while for chloride to chlorine gas, \( E^\circ_{\text{Cl}^-/\text{Cl}_2} = +1.36 \, \text{V} \). In the electrolysis of aqueous NaCl, chloride ions are more readily oxidized to chlorine gas because the chloride ions are present in much higher concentration compared to oxygen in the solution. Therefore, despite the more positive potential for oxygen reduction, chlorine is liberated at the anode due to the high concentration of chloride ions.