Electrolytic Refining Process of Blister Copper

To determine the correct statements regarding the electrolytic refining of blister copper, let us analyze the electrochemical setup and reactions involved in this process:

1. Electrodes Setup:

   • Anode (Positive Electrode): Blocks or strips of crude, impure copper (blister copper) are made the anode. During electrolysis, copper from the impure anode dissolves into the electrolyte: $\text{Anode (Oxidation): } \text{Cu (impure, s)} \rightarrow \text{Cu}^{2+}(\text{aq}) + 2e^{-}$ Therefore, Statement (A) is incorrect because the impure copper strip acts as the anode, not the cathode.

2. Electrolyte:

   • An aqueous solution of copper sulphate ($\text{CuSO}_4$) acidified with dilute sulfuric acid ($\text{H}_2\text{SO}_4$) is used as the electrolyte to enhance ionic conductivity and prevent hydrolysis of $\text{Cu}^{2+}$ ions. Therefore, Statement (B) is correct.

3. Cathode Reactions and Metal Deposition:

   • Cathode (Negative Electrode): Thin sheets of pure copper are used as the cathode. The $\text{Cu}^{2+}$ ions from the electrolyte migrate to the cathode and undergo reduction to form pure copper metal: $\text{Cathode (Reduction): } \text{Cu}^{2+}(\text{aq}) + 2e^{-} \rightarrow \text{Cu (pure, s)}$ Therefore, Statement (C) is correct.

4. Anode Mud Formation:

   • Impurities present in blister copper fall into two categories:
     • More electropositive metals than copper (e.g., $\text{Fe}$, $\text{Zn}$, $\text{Ni}$) dissolve into the solution as soluble ions.
     • Less electropositive metals (noble impurities) such as silver ($\text{Ag}$), gold ($\text{Au}$), platinum ($\text{Pt}$), antimony ($\text{Sb}$), selenium ($\text{Se}$), and tellurium ($\text{Te}$) do not dissolve and settle down at the bottom of the cell directly below the anode as anode mud. Therefore, Statement (D) is correct.

Thus, the correct statements are (B), (C), and (D).