Question

In the leaching of $A{g}_{2}S$ with NaCN, a stream of air is also passed. Which of the following is the correct explanation for this step?

• A. Reversible nature of reaction between $A{g}_{2}S$ and $NaCN$
• B. To oxidize $N{a}_{2}S$ formed into $N{a}_{2}S{O}_4$ and sulphur
• C. both (1) and (2)
• D. both are not suitable

Answer 1

The correct option is C both (1) and (2)

Reactions that occur are:
$A{g}_{2}S+4NaCN\to 2Na\left[Ag\right(CN{)}_2]+N{a}_{2}S$ (reversible reaction)
$4N{a}_{2}S+5O_2+H_{2}O\to 2N{a}_{2}S{O}_4+4NaOH+2S$

This NaOH formed increases the solubility of ${Ag}_{2}S$ in the mixture.

Also, the conversion of ${Na}_{2}S$ stops the first reaction from going in the backward direction.