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

Answer

`4Au (s) + 8CN^(-) (aq) +2H_(2)O(aq) +O_(2) (g) rarr 4 [Au (CN)_(2)]^(-) (aq) + 4OH^(-)(aq)`
`2[Au(CN)_(2)]^(-) (aq) + ZN(s) rarr 2Au(s) +[Zn(CN)_(4)]^(2-) (aq)`
In this reaction zinc acts as a reducing agent.