General Principles and Processes of Isolation of Elements - Result Question 8
####8. Extraction of gold and silver involves leaching with $CN^{-}$ion. Silver is later recovered by [2017]
(a) distillation
(b) zone refining
(c) displacement with $Zn$
(d) liquation
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Solution:
- (c) $Zn$ being more reactive than $Ag$ and $Au$, displaces them.
$ \begin{aligned} 4 Ag+8 NaCN+2 H_2 O+O_2 \xrightarrow{\text{ Leaching }} \\ 4 Na[Ag(CN)_2]+4 NaOH \end{aligned} $
Soluble Sodium dicyanoargentate (I)
Soluble cyanide compound can be treated with $Zn$ to give metal by displacement.
$ 2 Na[Ag(CN)_2]+Zn \xrightarrow[Na_2[Zn(CN)_4]+2 Ag \downarrow]{\text{ Displacement }} $
