Question

Explain how, mercury is extracted from its sulphide ore (cinnabar). Give equations of the reactions involved.

Answer 1

Mercury is a less reactive metal, which is quite low in the activity series. Mercury metal can be extracted just by heating its sulphide ore in air.

Mercury metal is derived from the sulphide mineral known as cinnabar, HgS, which is mercury (II) sulphide. The process of extracting mercury from cinnabar ore consists of two stages:

(i) The concentrated mercury (II) sulphide ore (cinnabar ore) is roasted in air, when mercury (II) oxide is formed.

\[\ce{\underset{(Cinnabar ore)}{\underset{Mercury (II) sulphide}{2HgS_{(s)}}} + \underset{(From air)}{\underset{Oxygen}{3O2_{(g)}}} ->[Roasting] \underset{Mercury (II) oxide}{2HgO_{(s)}} + \underset{Sulphur dioxide}{2SO2_{(g)}}}\]

(ii) When this mercury (II) oxide is heated to about 300°C, it decomposes (gets reduced) to form mercury metal.

\[\ce{\underset{(Formed above)}{\underset{Mercury (II) oxide}{2HgO_{(s)}}} ->[Heat][(Reduction)] \underset{Mercury metal}{2Hg_{(l)}} + \underset{Oxygen}{O2_{(g)}}}\]

Thus, here mercury metal has been produced by the reduction of mercury (II) oxide by heat alone.