Question

A mixture contains two salts which gives following results.

Answer 1

Bi³⁺ and Pb²⁺

Answer 2

1. Precipitation step:
   On treating the mixture with H₂S in dilute HCl, two types of sulfides can form. However, note that PbS dissolves in (yellow) ammonium sulfide, while Bi₂S₃ does not.

   • Thus, Bi³⁺ → Bi₂S₃ (insoluble in ammonium sulfide).

2. Acid treatment:
   When the precipitate is treated with HNO₃, the Bi₂S₃ (insoluble in ammonium sulfide) remains as an insoluble residue (X). In contrast, the other salt (from Pb²⁺) had not precipitated as its sulfide because PbS dissolves in ammonium sulfide; hence Pb²⁺ remains in solution (filtrate).

3. Sulfate precipitation:
   Addition of H₂SO₄ to the filtrate brings about the precipitation of PbSO₄ as a white solid (Y). This confirms the presence of Pb²⁺ in the filtrate.

4. Confirmation of residue:
   The residue (X), which is Bi₂S₃, dissolves in aqua regia – a property characteristic of bismuth compounds.

Thus, the two basic radicals present (i.e. the cations) in the original mixture are Bi³⁺ and Pb²⁺.