Question

Which sulphide is soluble in\[{\left( {N{H_4}} \right)_2}C{O_3}\]​?
A.\[SnS\]
B.\[A{s_2}{S_3}\]
C.\[S{b_2}{S_3}\]
D.\[CdS\]

Answer 1

Hint:In qualitative inorganic analysis, the cations belonging to the 2^nd analytical group precipitate out as sulphides. Solutions of ammonium salts are useful for differentiating the sulphides of these cations.

Complete step-by-step answer:
The qualitative inorganic analysis is a method in analytical chemistry that aims to determine the elemental composition of a given inorganic compound (or a mixture of compounds). This form of analysis mostly focuses on the detection of the ions of the given inorganic compound in an aqueous solution therefore, compounds in other forms may need to be brought into an aqueous solution first by certain standard methods before the analysis can proceed.
The ions are detected by treating the aqueous solution with certain reagents to check for the characteristic reactions of the ions present. The characteristic reactions mostly cause precipitate formation or a colour change.
In qualitative inorganic analysis, anions and cations are tested separately.
Both anions and cations are classified into analytical groups based on their properties and their reactions to certain reagents.
Cations are divided into six analytical groups. Each group has a common reagent which is used to separate the cations of that group from the aqueous solution of the given inorganic compound.
The 2^nd analytical group involves cations of cadmium (\[C{d^{2 + }}\] ), tin (\[S{n^{2 + }},S{n^{4 + }}\] ), arsenic (\[As{}^{3 + },A{s^{5 + }}\] ), antimony (\[S{b^{3 + }},S{b^{5 + }}\] ), copper (\[C{u^{2 + }}\] ) and bismuth (\[B{i^{3 + }}\] ). These cations precipitate as acid-insoluble sulphides. Apart from cadmium sulphide (\[CdS\]), the sulphides of all other cations are indistinguishable visually. However, an ammoniacal solution can be used to distinguish them due to the selective solubility of the cations.
Arsenic trisulphide (\[A{s_2}{S_3}\]) is soluble in ammonium carbonate (\[{\left( {N{H_4}} \right)_2}C{O_3}\]). Their reaction is as follows:
\[A{s_2}{S_3}(aq) + 3{(N{H_4})_2}C{O_3}(aq) \to 3C{O_{2}}(g) + {(N{H_4})_{3}}As{O_3}(aq) + {(N{H_4})_3}As{S_3}(aq)\]
Thus, option B is correct.

Note:Remember that while the sulphide of arsenic is soluble in ammonium carbonate, the sulphides of tin, arsenic and antimony are soluble in yellow ammonium sulphide. Please be mindful of which ammonia solution is mentioned in the question.