Question

Yellow ammonium sulphide solution is a suitable reagent for separation of:
(A) $HgS$ and $PbS$
(B) $PbS$ and $B{{i}_{2}}{{S}_{3}}$
(C) $B{{i}_{2}}{{S}_{3}}$ and $CuS$
(D) $CdS$ and $A{{s}_{2}}{{S}_{3}}$

Answer 1

Hint: Sulphide of arsenic, tin is soluble in yellow ammonium sulphide. Sulfides of cadmium are insoluble in yellow ammonium sulphide. Yellow ammonium sulphide is used to separate sulphide of group llA and group llB.

Complete solution step by step:
- Qualitative inorganic analysis is used to detect ions in aqueous solution.
- Solutions are treated with various reagents and reactions may cause precipitation, color change or any other visible changes.
- Cations are divided into six groups according to properties.
First analytical group consists of ions which form insoluble chlorides.
 Second analytical group consists of ions which form acid insoluble sulphide.
- The reagents used are any substance that gives sulphide ions in solution.
- Basic sulphides are insoluble in yellow ammonium sulphide and are grouped as llA. Acidic sulphides are soluble in yellow ammonium sulphide due to complex formation. They are grouped as llB.
- Sulphides of mercury, lead, bismuth, copper and cadmium are basic in nature.
- Sulphides of arsenic, tin and antimony are acidic in nature.
- The sulphides of arsenic, tin, and antimony are soluble in yellow ammonium sulphide solution as they form polysulphide complexes. Sulphides of arsenic are acidic in nature.
- When Cadmium sulphide is added in water then hydrochloric acid is added followed by hydrogen sulphide gas, yellow precipitate is formed. Sulfides of cadmium are basic in nature.

Hence, Yellow ammonium sulphide solution is a suitable reagent for separation of (D) $CdS$ and $A{{s}_{2}}{{S}_{3}}$.

Note:
Cations in second group include:
$C{{d}^{+2}}, B{{i}^{+3}}, C{{u}^{+2}}, A{{s}^{+3}}, A{{s}^{+5}}, S{{b}^{+5}}, S{{b}^{+3}}, S{{n}^{+2}}, S{{n}^{+2}}, S{{n}^{+4}}, H{{g}^{+2}}, P{{b}^{+2}}$. The precipitates of these cannot be distinguished except cadmium sulphide which is yellow. Except mercury sulphide, all sulphides are soluble in dilute nitric acid. Copper sulphide dissolves in ammonia giving an intense blue solution whereas cadmium sulphide gives a colorless solution.