Question

Write the role of :
(i) NaCn in the extraction of gold from its ore.
(ii) Cryolite in the extraction of aluminium from pure alumina.
(iii) Co in the purification of Nickel.

Answer 1

(i) Leaching of gold ore occurs in the presence of air from which the gold is obtained later by displaacement method.
`4Au(s)+8CN^(-)(aq)+2H_2O(aq)+O_2(g) to 4[Au(CN)_2]^(-)+4OH^(-)(aq)`
`2[Au(CN_2]^(-)Zn(s) to [Zn(CN_4]^(2-)(aq)+2Au(s)`
(ii) In order to decrease the melting point of mixture and to increase the conductivity of alumina `(Al_2O_3)`, cryolite is added in the metallurgy of Al.
(iii) Impure Nickel reacts with CO to form volatile tetracarbonyl nickel (o) which on heating forms pure nickel.