Ncert Exercises & Solutions

Extraction of gold and silver involves leaching the metal with $C N^{-}$ ion. The metal is recovered by ......

1.	Displacement of metal by some other metal from the complex ion.
2.	Roasting of metal complex.
3.	Calcination followed byroasting.
4.	Thermal decomposition of metal complex.

Extraction of gold and silver involves leaching the metal with

C N^{-}

ion. The metal is recovered by displacement of metal by some other metal from the complexion. This is an oxidation reaction.

4 Au (s) + 8 {CN}^{-} (aq) + 2 H_{2} O (aq) + O_{2} (g) \to 4 {[Au {(CN)}_{2}]}^{-} (aq) + 4 {OH}^{-} (aq)

4 [Au {(CN)}_{2}] (aq) + Zn (s) \to 2 Au (s) + {[Zn {(CN)}_{4}]}^{2 -} (aq)

Here, Zn acts as a reducing agent