Question

Sodium thiosulphate is prepared by:

• A. boiling $N{a}_{2}S{O}_3$ solution with elemental sulphur in alkaline medium
• B. boiling $N{a}_{2}S{O}_3$ solution with elemental sulphur in acidic medium
• C. oxidation of poly sulphides, $N{a}_2{S}_3$ with air
• D. reduction of bisulphite solution plus $S{O}_2$ with zinc dust

Answer 1

Answer: (A), (C)

The correct options are
A boiling $N{a}_{2}S{O}_3$ solution with elemental sulphur in alkaline medium
C oxidation of poly sulphides, $N{a}_2{S}_3$ with air

(A) $N{a}_{2}S{O}_3+s\underset{O{H}^{-}or{H}_{2}O}{\overset{boiling}{\to }}N{a}_2{S}_2{O}_3$
(B) $S_2{O}_3^{2-}$ formed in presence of acid precipitates sulphur and liberates $S{O}_2$ gas according to the following reaction.
$S_2{O}_3^{2-}+H^{+}\to S\underset{disproportionation}{\downarrow \left(white\right)}+S{O}_2\uparrow H_{2}O$
(C) $2N{a}_2{S}_3+3O_2\underset{air}{\overset{heating}{\to }}2N{a}_2{S}_2{O}_3+2S$
(D) $2HS{O}_3^{-}+S{O}_2\stackrel{Zn}{\to }{S}_2{O}_4^{2-}+S{O}_3^{2-}+H_{2}O$