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Chemistry

Explain the following:

(a) Zinc oxide can be reduced to zinc by using carbon monoxide, but aluminium oxide cannot be reduced by reducing a agent.

(b) During electrolysis of molten lead bromide, a graphite anode is preferred to other electrodes.

(c) Electrolysis of molten lead bromide is considered to be a redox reaction.

Electrolysis

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Answer

(a) Aluminium is placed above zinc in reactivity series. Hence, aluminium is more reactive than zinc and its oxide is stable and cannot be reduced by a reducing agent. Zinc being less reactive metal, its oxide is less stable and so it can be easily reduced by carbon monoxide.

(b) As graphite is unaffected by the reactive bromine vapours released at the anode hence, a graphite anode is preferred during the electrolysis of molten lead bromide

(c) Electrolysis of molten lead bromide involves oxidation and reduction reactions and hence is a redox reaction.

Reduction reaction at cathode:

Pb2+ + 2e- ⟶ Pb

Oxidation reaction at the anode:

Br1- - 1e2- ⟶ Br

Br + Br ⟶ Br2

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