Question

If colourless solutions of $N{a}_{2}S$ and $N{a}_{2}S{O}_3$ in water are taken in two separate unknown test tubes, then $S^{2-}$ and $S{O}^{2-}$ can be distinguished by using which one of the following test?

• A. Lead acetate test
• B. Barium chloride test
• C. Sodium nitroprusside test
• D. Methylene blue test

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A Lead acetate test
B Barium chloride test
C Sodium nitroprusside test
D Methylene blue test

Reactions:

(A) $S{O}_3^{2-}+P{b}^{2+}\to PbS{O}_3\downarrow \left(\text{white}\right)$
$S^{2-}+P{b}^{2+}\to PbS\downarrow \left(\text{black}\right)$
(B) $S{O}_3^{2-}+B{a}^{2+}\to BaS{O}_3\downarrow \left(\text{white}\right)$
$S^{2-}+B{a}^{2+}\to \text{No precipitate}$
(C) $S{O}_3^{2-}+N{a}_2\left[Fe\right(CN{)}_{5}NO]\to N{a}_4[Fe\left(CN{)}_{5}NO\right]\left(\text{purple violet colouration}\right)$
$S^{2-}+N{a}_2\left[Fe\right(CN{)}_{5}NO]\to N{a}_4[Fe\left(CN{)}_5\right(NOS\left)\right]\left(\text{purple colouration}\right)$
(D) Soluble sulphide gives this test with N,N-dimethyl-p-phenylenediamine in strongly acidic solution containing iron(iii) chloride.