Question 2(2016)
Write equations for the reactions taking place at the two electrodes during the electrolysis of:
(i) Acidified CuSO4 solution with copper electrodes.
(ii) Molten PbBr2 with inert electrodes. (mention clearly the name of the electrode in each case)
(i) Electrode — Cathode : Copper, Anode : Copper
Dissociation of aq. CuSO4 :
CuSO4 ⇌ Cu2+ + SO42-
H2O ⇌ H1+ + OH1-
H2SO4 ⇌ 2H1+ + SO42-
Reaction at cathode [pure thin sheet of Cu]:
Cu2+ + 2e- ⟶ Cu [Cu deposited on thin sheet]
Reaction at anode [impure block of active Cu]:
Cu - 2e- ⟶ Cu2+ [product nil - Cu2+ ions]
(ii) Electrode — Cathode : Iron or Graphite, Anode : Graphite
Dissociation of molten PbBr2 : PbBr2 ⇌ Pb2+ (cathode) + 2Br1- (anode)
Reaction at cathode:
Pb2+ + 2e- ⟶ Pb [product lead metal]
Reaction at anode:
Br1- - 1e-⟶ Br
Br + Br ⟶ Br2