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.

1. What is the cathode and anode made of in the refining of copper by this process? (1)
2. Name the solution used in the above process and write its formula. (1)
3.    
   1. How copper gets refined when electric current is passed in the electrolytic cell? (2)
      OR
   2. 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 'X and a strip of silver in beaker 'B'? Give reason for your observations in each case. (2)

Answer 1

Electrolytic Refining of Copper

1. Cathode and Anode:

   • Cathode: A thin strip of pure copper.
   • Anode: A block of impure copper.

2. Solution Used:

   • The solution used is acidified copper sulfate solution.
   • Formula: CuSO4​ (Copper sulfate).

1. Process of Refining: When electric current is passed through the electrolytic cell:
   • At the anode (impure copper): Impure copper gets oxidized. Copper ions (Cu²⁺) dissolve into the solution, leaving impurities behind as anode mud. 
     \[\ce{Cu(s) -> Cu^2+ (aq) + 2e^-}\]
   • At the cathode (pure copper strip): Copper ions (Cu²⁺) from the solution get reduced and deposit on the pure copper strip. 
     \[\ce{Cu^2 + (aq)+ 2e^- -> Cu(s)}\]

This process leads to the gradual purification of copper.

OR: Reaction of Zinc and Silver with Copper Sulfate

Beaker A (Zinc Strip in Copper Sulfate Solution):

Observation:

• The zinc strip gets coated with a reddish-brown layer of copper.
• The blue color of the copper sulfate solution fades gradually.

Reason:

• Zinc is more reactive than copper, so it displaces copper from copper sulfate: 
  \[\ce{Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s)}\]

Beaker B (Silver Strip in Copper Sulfate Solution):

Observation: No visible change is observed.

Reason: Silver is less reactive than copper, so it cannot displace copper from copper sulfate. There is no reaction:

No Reaction