Question

State your observations for the following electrolytic reactions:
(a) Solid copper sulphate is electrolysed between platinum electrodes.
(b) Aqueous copper sulphate is electrolysed between platinum electrodes.
(c) Aqueous copper sulphate is electrolysed between copper electrodes.

Answer 1

The observations for the following electrolytic reactions are explained as follows:

(a) Solid copper sulphate is electrolysed between platinum electrodes - No reaction takes place in the electrolytic cell. As the ions present in solid copper sulphate are held very tightly and are unable to move, electricity cannot pass through them. Only when this solid copper sulphate is fused or is in its aqueous state, ions become mobile and electric current is able to pass through them, leading to the electrolytic reactions.

(b) Aqueous copper sulphate is electrolysed between platinum electrodes - During this electrolysis reaction, copper metal is deposited at cathode and oxygen gas is liberated at anode. In the electrolyte, the blue colour of copper sulphate becomes paler and sulphuric acid is formed.

(c) Aqueous copper sulphate is electrolysed between copper electrodes - During this electrolysis reaction, copper ions are generated at anode, that go into the electrolyte (i.e., copper sulphate solution). Then, these copper ions from the electrolyte are deposited at cathode. As the copper ions in the copper sulphate solution remain the same, there will be no change in the intensity of the blue colour of the copper sulphate solution. Further in the process, the anode becomes thin and the cathode becomes thicker with the deposition of reddish brown copper metal over it.