Question

The metals produced by various reduction processes are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining.
(i) What is the cathode and anode made of in the refining of copper by this process?
(ii) Name the solution used in the above process and write its formula.
(iii) (A) How copper gets refined when electric current is passed in the electrolytic cell?
OR
(iii) (B) You have two beakers ‘A’ and ‘B’ containing copper sulphate solution. What would you observe after about 2 hours if you dip a strip of zinc in beaker ‘A’ and a strip of silver in beaker ‘B’? Give reason for your observations in each case.

Answer 1

Step 1: Understanding Electrolytic Refining of Copper:
Electrolytic refining is a standard method for purifying metals. It involves using the impure metal as the anode and a thin strip of pure metal as the cathode. Metal ions migrate from the impure anode to the cathode, where they deposit as pure metal.

Part (i): Composition of Cathode and Anode in Copper Refining:
For the electrolytic refining of copper:
- The anode consists of impure copper, which includes other metals and impurities.
- The cathode is a thin strip of pure copper that accumulates pure copper deposits throughout the process.

Part (ii): Electrolyte Solution and Formula:
The solution employed in the electrolytic refining of copper is copper(II) sulfate solution. Its chemical formula is:
- CuSO₄ (Copper sulfate solution).

Part (iii) (A): Copper Refinement Mechanism:
When electric current is applied to the electrolytic cell containing copper sulfate solution:
- At the anode, copper from the impure anode dissolves into the solution, forming copper ions (Cu²⁺). Impurities like iron, silver, and gold do not dissolve and form anode mud.
- At the cathode, copper ions (Cu²⁺) in the solution accept electrons (reduction) and are deposited as pure copper metal.
Consequently, pure copper plates the cathode, while impurities remain at the anode or are collected as sludge.

Part (iii) (B): Observations with Zinc and Silver in Copper Sulfate Solution:
- Beaker A (Zinc strip in copper sulfate solution):
After approximately 2 hours, the zinc strip will be coated with copper metal. This is due to zinc's higher reactivity compared to copper, causing it to displace copper from the copper sulfate solution. The displaced copper deposits onto the zinc strip.
The relevant reaction is:

  Zn(s) + CuSO4 → ZnSO4(aq) + Cu(s)  

This results in the zinc strip being coated with copper.

- Beaker B (Silver strip in copper sulfate solution):
No significant observable change will occur after approximately 2 hours. This is because silver is less reactive than copper, and therefore, it cannot displace copper from the copper sulfate solution. No copper deposition will be observed on the silver strip.

Summary of Findings:
- In Beaker A, zinc displaces copper and becomes coated with it.
- In Beaker B, no reaction occurs as silver lacks the reactivity to displace copper.