Extraction of gold and silver involves leaching the metal with `CN^(-)` ion. The metal is recovered by _______

Options

A. displacement of metal by some metal from the complex ion.
B. roasting of metal complex
C. calcination followed by roasting
D. thermal decomposition of metal complex

Answer

A

Explanation

(a) Extraction of gold and silver involves leaching the metal with `CN^(-)` ion. The metal is recovered by displacement of metal by some other metal from the complex ion. This is an oxidation reaction.
`4Au(s) + 8CN^(-)(aq) +2H_(2)O(aq) + O_(2)(g) to 4[Au(CN)_(2)]^(-) (aq) + 4OH^(-)(aq)`
`" "4[Au(CN)_(2)](aq)+Zn(s) to 2Au(s) +[Zn(CN)_(4)]^(2-)(aq)`
Here , Zn acts as a reduction agent.