Question

Select the correct answer from the list given in brackets. What is discharged at the Cathode during electrolysis of copper sulphate using copper electrodes as anode and cathode [${\mathrm{Cu}}^{2+},{\mathrm{OH}}^{-},{\mathrm{SO}}_4^{2-},{\mathrm{H}}^{+}$].

Answer 1

Electrolysis is a process of dissociation of a compound into ions on the passing of electric current into an electrolytic solution.

Electrolysis of copper sulphate (${\mathrm{CuSO}}_4$):

$$\begin{gathered} {\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)+{\mathrm{SO}}_4^{2-}\left(\mathrm{aq}\right) \\ \mathrm{copper}\mathrm{copper}\mathrm{sulphate} \\ \mathrm{sulphate}\mathrm{ion}\mathrm{ion} \end{gathered}$$

At anode: Oxidation of hydroxide ions (${\mathrm{OH}}^{-}$) occur by lose of electrons.

${\mathrm{OH}}^{-}\to \mathrm{OH}+{\mathrm{e}}^{-}$

$$\begin{gathered} 2{\mathrm{OH}}^{-}\to {\mathrm{H}}_2\mathrm{O}+\frac{1}{2}{\mathrm{O}}_2+2{\mathrm{e}}^{-} \\ \mathrm{hydroxide}\mathrm{water}\mathrm{oxygen} \\ \mathrm{ion} \end{gathered}$$

At cathode: Reduction of ${\mathrm{Cu}}^{2+}$ ions occur by gain of two electrons.

$$\begin{gathered} {\mathrm{Cu}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Cu} \\ \mathrm{copper}\mathrm{copper} \\ \mathrm{ion}\mathrm{atom} \end{gathered}$$

So, ${\mathrm{OH}}^{-}$ion is discharged at anode and ${\mathrm{Cu}}^{2+}$ is discharged at cathode.