Write the chemical reaction involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.

Explanation

(i) `4Au(s)+8CN^(-)(aq)+2H_(2)O(aq)+O_(2)(g) to 4[Au(CN)_(2)]^(-)(aq)+4OH^(-)(aq)`
(ii) `2[Au(CN)_(2)]^(-)(aq)+Zn(s) to 2Au(s)+[Zn(CN)_(4)]^(2-)(aq)`
Zinc acts as a reducing agent in this reaction .