Question

A salt mixture consists of a yellow solid (A) and a colourless solid (B). The aqueous solution of the mixture
(i) On passing $H_{2}S$, we get a black precipitate of (C), which dissolves only in aqua-regia. On extraction and reaction with $SnC{l}_2$ a greyish white precipitate is obtained.
(ii) On treatment with ammonium hydroxide a reddish brown precipitate (D) is obtained.
The sodium extract of the solution gives the following tests:
(i) On reaction with $AgN{O}_3$ it gives a yellow precipitate which is insoluble in $N{H}_3.$
(ii) On shaking with $FeC{l}_3$ and $CC{l}_4$ a violet colouration in $CC{l}_4$
layer is obtained.
Mixture on performing flame test gives lilac colour. Identify the compounds (A), (B), (C) and (D).

Answer 1

$\underset{\text{Mixture}}{\underbrace{A+B}}⟶$ lilac colour in flame
(i) $\underset{\text{Mixture}}{\underbrace{A+B}}\stackrel{H_{2}S}{\to }\underset{\text{Black}}{C\downarrow }$
(ii) $C\underset{\text{in aqua-regia}}{\overset{\text{Soluble}}{\to }}$ Soluble $\stackrel{\text{Evaporation}}{\to }$ Residue
$\stackrel{SnC{l}_2}{\to }$ Greyish black $\downarrow (D)$
$\Rightarrow C$ is $HgS$.
(iii)$\underset{\text{Solution of mixture}}{\underbrace{A+B}}\stackrel{N{H}_{4}OH}{\to }$ Brown ppt.
Sodium extract of salt $\stackrel{CC{l}_4/FeC{l}_3}{\to }$ Violet layer
Sodium extract $\stackrel{AgN{O}_3}{\to }$ Yellow ppt $\stackrel{N{H}_3}{\to }$ Insoluble
$\Rightarrow A=KI$ and $B=Hg{I}_2.$