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 widely used method for purifying metals. In this process, the impure metal is made the anode and a thin strip of pure metal is made the cathode. The metal ions from the impure metal move toward the cathode, where they get deposited as pure metal.

Part (i): What is the cathode and anode made of in the refining of copper by this process?
In the electrolytic refining of copper:
- The anode is made of impure copper (containing other metals and impurities).
- The cathode is made of pure copper (a thin strip of copper that gets gradually coated with pure copper during the process).

Part (ii): Name the solution used in the above process and write its formula.
The solution used in the electrolytic refining of copper is copper(II) sulfate solution. Its formula is:
- CuSO₄ (Copper sulfate solution).

Part (iii) (A): How copper gets refined when electric current is passed in the electrolytic cell?
When electric current is passed through the copper sulfate solution in the electrolytic cell:
- At the anode, copper metal from the impure copper dissolves into the solution as copper ions (Cu²⁺). The impurities (like iron, silver, and gold) do not dissolve and remain behind as anode mud.
- At the cathode, the copper ions (Cu²⁺) in the solution gain electrons (are reduced) and deposit as pure copper metal.
Thus, pure copper is deposited on the cathode, and the impurities remain at the anode or are removed as sludge.

Part (iii) (B): You have two beakers ‘A’ and ‘B’ containing copper sulfate 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.
- Beaker A (Zinc strip in copper sulfate solution):
After about 2 hours, you will observe that the zinc strip has become coated with copper metal. This happens because zinc is more reactive than copper. Zinc displaces copper from the copper sulfate solution, and copper metal gets deposited on the zinc strip.
The reaction that occurs is:

  Zn(s) + CuSO4 → ZnSO4(aq) + Cu(s)
  

So, the zinc strip becomes coated with copper.

- Beaker B (Silver strip in copper sulfate solution):
After about 2 hours, there will be no noticeable change. This is because silver is less reactive than copper, and it cannot displace copper from the copper sulfate solution. No copper will be deposited on the silver strip.

Conclusion:
- In beaker A, zinc displaces copper and becomes coated with copper.
- In beaker B, no reaction takes place as silver cannot displace copper.