Question

A light bluish green crystalline compound responds to the following tests
(i) Its aqueous solution gives a brown precipitate or colouration with $K_2[Hg{I}_4]$.
(ii) Its aqueous solution gives a blue colour with $K_3[Fe(CN{)}_6]$.
(iii) Its solution in hydrochloric acid gives a white precipitate with $BaC{l}_2.$
Identify the ions present and suggest the formula of the compound.

Answer 1

(i) Brown precipitate or colour with $K_{2}Hg{I}_4$, indicates the presence of $N{H}_4^{+}$ ion.
(ii) Aqueous $Fe(ll)$ solution gives a blue colour with
$K_3[Fe(CN{)}_6]$ due to formation of $Fe[Fe(CN{)}_6{]}^{-}$ ion :
$F{e}^{2+}+Fe(CN{)}_6^{3-}⟶\underset{\text{Blue colouration}}{Fe[Fe(CN{)}_6{]}^{-}}$
(iii) Aqueous solution of $S{O}_4^{2-}$ ion in $HCl$ gives white ppt with $BaC{l}_2$ solution
$S{O}_4^{2-}+BaC{l}_2⟶BaS{O}_4\downarrow +2C{l}^{-}$