Question

A metal chloride $X$ shows the following reactions.
(i) When $H_{2}S$ is passed in an acidified aqueous solution of $X$, a black precipitate is obtained
(ii) The precipitate obtained at step (i) is not soluble in yellow ammonium sulphide.
(iii) When a solution of stannous chloride is added to an aqueous solution of $X$, a white precipitate is obtained which turns grey on addition of more of stannous chloride.
(iv) When an aqueous solution of $KI$ is added to an aqueous solution of ($X$), a red precipitate is obtained which dissolves on addition of excess of $KI$.
Identify $X$.

• A. $HgC{l}_2$
• B. $CaC{l}_2$
• C. $SiC{l}_2$
• D. None of these

Answer 1

Answer: (A)

$HgC{l}_2$

The metal chloride $X$ is mercuric chloride $HgC{l}_2$.
(i) It reacts with hydrogen sulphide to form mercuric sulphide.
$HgC{l}_2+H_{2}S⟶HgS+2HCl$
(iii) It reacts with stannous chloride to form white precipitate of mercurous chloride along with formation of stannic chloride.
$2HgC{l}_2+SnC{l}_2⟶\underset{white}{H{g}_{2}C{l}_2}\downarrow +SnC{l}_4$
Mercurous chloride reacts with stannous chloride to form grey mercury metal.
$H{g}_{2}C{l}_2+SnC{l}_2⟶\underset{grey}{2Hg}\downarrow +SnC{l}_4$
(iv) Mercuric chloride reacts with potassium iodide to form orange ppt. of mercuric iodide.
$HgC{l}_2+2KI⟶\underset{orange}{Hg{I}_2}\downarrow$
Mercuric iodide reacts with $KI$ to form Nessler's reagent which is soluble in water.
$Hg{I}_2+2KI⟶\underset{soluble}{K_{2}Hg{I}_4}$