Chemistry - Electrochemistry Question with Solution | TestHub

Sodium chloride in water dissociates as: $\begin{array}{rl}\mathrm{NaCl}& \rightleftharpoons {\mathrm{Na}}^{+}+{\mathrm{Cl}}^{-}\\ {\mathrm{H}}_2\mathrm{O}& \rightleftharpoons {\mathrm{H}}^{+}{\mathrm{OH}}^{-}\end{array}$ When electric current is passed through this solution using platinum electrodes. ${\mathrm{Na}}^{+}$and ${\mathrm{H}}^{+}$move towards cathode whereas ${\mathrm{Cl}}^{-}$and ${\mathrm{OH}}^{-}$ions move towards anode. At cathode $\begin{array}{rl}{\mathrm{H}}^{+}+e^{-}& \to \mathrm{H}\\ \mathrm{H}+\mathrm{H}& \to {\mathrm{H}}_2\end{array}$ An anode $\begin{array}{rl}{\mathrm{Cl}}^{-}& \to \mathrm{Cl}+e^{-}\\ \mathrm{Cl}+\mathrm{Cl}& \to {\mathrm{Cl}}_2\end{array}$ If mercury is used as cathode ${\mathrm{H}}^{+}$ ions are not discharged at mercury cathode because mercury has a high hydrogen over voltage. ${\mathrm{Na}}^{+}$ ions are dischaged at cathode in preference of ${\mathrm{H}}^{+}$ions yielding sodium, which dissolves in mercury to form amalgam