Question

The purpose of stream of air in leaching process of $A{g}_{2}S$ is to?

• A. $\text{Oxidises}N{a}_{2}S\text{formed into}N{a}_{2}S{O}_4$
• B. $\text{Oxidises}N{a}_{2}S\text{formed into}N{a}_{2}O$
• C. Act as catalyst
• D. None of the above

Answer 1

The correct option is A $\text{Oxidises}N{a}_{2}S\text{formed into}N{a}_{2}S{O}_4$

In leaching of $A{g}_{2}S$ (silver sulphide) with aq $NaCN$, a stream of air is passed.
Silver forms a soluble complex $Na\left[Ag\right(CN{)}_2]$.
$A{g}_{2}S+4NaCN\rightleftharpoons 2Na\left[Ag\right(CN{)}_2]+N{a}_{2}S$
Sodium cyanide is unstable in water and liberates hydrogen sulphde and Sodium hydroxide.
Passing of oxygen converts the Sodium sulphide into $NaOH$ and precpitates $S$.
$2N{a}_{2}S+O_2+2H_{2}O\rightleftharpoons 4NaOH+2S$
Removal of a product(s) favours the complexation of silver because reversible nature of reaction between $A{g}_{2}S\text{and}NaCN$ and to oxidise $N{a}_{2}S$ formed into $N{a}_{2}S{O}_4$ and sulphur.