Question

Select the correct answer from the list given in the brackets:

The ion which is discharged at the anode during the electrolysis of copper sulfate solution using copper electrodes as anode and cathode.

$\left[{\mathrm{Cu}}^{2+},{\mathrm{OH}}^{-},{{\mathrm{SO}}_4}^{2-},{\mathrm{H}}^{+}\right]$

Answer 1

Electrolysis of aqueous Copper sulfate using copper electrodes

• Electrolysis is a process in which an electrolyte, in this example copper sulfate solution $\left({\mathrm{CuSO}}_4\right)$ (concentrated sulfuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$ is also added to increase the conductivity), performs redox reactions at the electrodes under the influence of an electric current.
• When the current passes through the electrolyte, ${\mathrm{Cu}}^{2+}$and ${\mathrm{H}}^{+}$ ions migrate towards the cathode, and ${{\mathrm{SO}}_4}^{2-}$and ${\mathrm{OH}}^{-}$ ions migrate towards the anode.

Electrolytic reactions

The reactions that occur are as follows

$$\begin{gathered} {\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)+{{\mathrm{SO}}_4}^{2-}\left(\mathrm{aq}\right) \\ {\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to 2{\mathrm{H}}^{+}+{{\mathrm{SO}}_4}^{2-}\left(\mathrm{aq}\right) \\ {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right) \end{gathered}$$

Reaction at the anode:

• Both Sulfate $\left({{\mathrm{SO}}_4}^{2-}\right)$ and Hydroxyl $\left({\mathrm{OH}}^{-}\right)$ ions migrate towards the anode, but neither of them is discharged due to the active nature of the anode.
• Since the anode is of copper, it loses 2 electrons and forms copper ions.
• The number of Copper ions furnished by the anode is equal to the number of copper ions discharged at the cathode.
• The chemical reaction is as follows

$\mathrm{Cu}\left(\mathrm{s}\right)-2{\mathrm{e}}^{-}\to {\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)$

Hence, the ion which is discharged at the anode during the electrolysis of aqueous copper sulfate is the Copper ion $\left({\mathrm{Cu}}^{2+}\right)$.