Question 5(iii)
State your observations during the process of electrolysis of given compounds.
(a) Fused lead bromide using graphite electrodes.
(b) Copper sulphate solution using copper electrodes.
(c) Acidified water using platinum electrodes.
(a) The observations at the anode & at the cathode are:
At cathode — silvery grey deposit of lead metal.
Reaction at cathode:
Pb2+ + 2e- ⟶ Pb
At anode — reddish brown fumes of bromine vapours.
Reaction at anode:
Br1- - 1e- ⟶ Br
Br + Br ⟶ Br2
(b) The observations at the anode & at the cathode are:
At cathode — Brownish pink copper metal is deposited at cathode during electrolysis of copper sulphate.
Reaction at cathode:
Cu2+ + 2e- ⟶ Cu
At anode — Copper ions are formed. Copper anode diminishes in mass.
Reaction at anode:
Cu - 2e- ⟶ Cu2+
The blue colour of copper sulphate solution does not fade.
(c) The observations at the anode & at the cathode are:
At cathode — Hydrogen gas is liberated at cathode.
Reaction at cathode:
H+ + e- ⟶ H
H + H ⟶ H2
At anode — Oxygen gas is liberated at anode.
Reaction at anode:
OH- ⟶ OH + e-
OH + OH ⟶ H2O + O
O + O ⟶ O2