Under the condition of electrolysis of aqueous sodium chloride, oxidation of water at anode requires over potential. $\mathrm{So}, \mathrm{Cl}^{-}$is oxidized at anode instead of water.

Possible oxidation half cell reactions occurring at anode are

$$\begin{array}{ll} \mathrm{Cl}^{-}(\mathrm{aq}) \longrightarrow \frac{1}{2} \mathrm{Cl}_2(g)+\mathrm{e}^{-} ; & E_{\mathrm{cell}}^{\mathrm{s}}=1.36 \mathrm{~V} \\ 2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow \mathrm{O}_2(g)+4 \mathrm{H}^{+}(\mathrm{aq})+4 \mathrm{e}^{-} ; & E_{\mathrm{cell}}^{\circ}=1.23 \mathrm{~V} \end{array}$$

Species having lower $E_{\text {cell }}^{\circ}$ cell undergo oxidation first than the higher value but oxidation of $\mathrm{H}_2 \mathrm{O}$ to $\mathrm{O}_2$ is kinetically so slow that it needs some overvoltage.

The potential difference between the electrode and the electrolyte in an electrochemical cell is called electrode potential.

The cell drawn above represents electrochemical cell in which two different electrodes are fitted in their respective electrolytic solution and cell drawn at bottom represents electrolytic cell.

Cell representation can be represented as $\mathrm{Zn}\left|\mathrm{Zn}^{2+} \| \mathrm{Cu}^{2+}\right| \mathrm{Cu}$.

Zn is loosing electrons which are going towards electrode (A) and copper is accepting electron from electrode B. Hence,

Charge on electrode $A=+$

Charge on electrode $B=-$

Alternating current is used in electrolysis so that concentration of ions in the solution remains constant and exact value of resistance is measured.

When an opposing potential of 1.1 V is applied to a galvanic cell having electrical potential of 1.1 V then cell reaction stops completely and no current will flow through the cell.