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 $SnCl_2$ 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 $AgNO_3$ it gives a yellow precipitate which is insoluble in $NH_3.$
(ii) On shaking with $FeCl_3$ and $CCl_4$ a violet colouration in $CCl_4$
layer is obtained.
Mixture on performing flame test gives lilac colour. Identify the compounds (A), (B), (C) and (D).

Answer 1

$\underbrace{A + B}_{\text{Mixture}} \ \longrightarrow \ $ lilac colour in flame
(i) $\underbrace{A + B}_{\text{Mixture}} \ \xrightarrow {H_2 S} \underset {\text{Black}}{C \downarrow}$
(ii) $C \xrightarrow [\text{in aqua-regia}] {\text{Soluble}} $ Soluble $ \xrightarrow {\text{Evaporation}} $ Residue
$ \xrightarrow {SnCl_2}$ Greyish black $ \downarrow (D)$
$ \Rightarrow C$ is $HgS$.
(iii)$\underbrace{A + B}_{\text{Solution of mixture}} \xrightarrow {NH_4 OH} $ Brown ppt.
Sodium extract of salt $\xrightarrow {CCl_4 / FeCl_3} $ Violet layer
Sodium extract $\xrightarrow {AgNO_3} $ Yellow ppt $\xrightarrow {NH_3} $ Insoluble
$ \Rightarrow A = KI $ and $ B = HgI_2.$