Question

Leaching of $A{g}_{2}S$ is carried out by heating it with a dilute solution of:

• A. $NaCN$ only
• B. $HCl$
• C. $NaOH$
• D. $NaCN$ in presence of $O_2$

Answer 1

The correct option is D $NaCN$ in presence of $O_2$

Leaching of $A{g}_{2}S$ is carried out by heating it with a dilute solution of NaCN in presence of $O_2$.
This forms a soluble complex $\left[Ag\right(CN{)}_2{]}^{-}$.

$A{g}_{2}S+4NaCN\rightleftharpoons 4N{a}^{+}+2\left[Ag\right(CN{)}_2{]}^{2-}+S^{2-}$

Here sulphide ion is oxidised to sulphate ion by oxygen.

Thus, soluble material can be separated from insoluble material.
Treatment of the cynaide compound with zinc gives displacement reaction in which silver is obtained.

$2Na\left[Ag\right(CN{)}_2]+Zn\to [Zn(CN{)}_4{]}^{2-}+2Ag\downarrow$