Explain the role of each of the following in the extraction of metals from their ores :
(i) CO in the extraction of nickel.
(ii) Zinc in the extraction of silver.
(iii) Silica in the extraction of copper.

Explanation

(i) Impure nickel reacts with Co to form volatile compound which on heating forms pure nickel.
`Ni+4COoverset(330-350k)tounderset("Volatile") (Ni(CO)_4)overset(450-470k)tounderset(("Pure"))(Ni+4CO)`.
(ii) Zinc in the extration of silver : Zn acts as reducing agent in the extraction of silver.
`2[Ag(CN)_2]^(-) (aq)+Zn(s) to2Ag(s) +[Zn(CN)_4]^(2-)(aq)]`
(iii) The ore is heated in a reverberatory furnance after mixing with silica. In the furnance, iron oxide slags of as iron silicate and copper is produced in the form of copper matte. This contains `Cu_2D and FeS`.
`FeO+SiO_2tounderset(("Slag"))(FeSiO_3)`