Consider the sulphides - HgS, PbS, CuS, Sb S , As S and CdS. Number of these sulphides soluble in 50 — Practical Organic Chemistry and Purification Chemistry Question
Question
Consider the sulphides - HgS, PbS, CuS, Sb S , As S and CdS. Number of these sulphides soluble in 50% HNO is ________. 2 3 2 3 3
💡 Solution & Explanation
**Step 1: Identify the solubility principle** Sulphides dissolve in dilute HNO₃ when the metal can be oxidized AND the sulphide is not extremely insoluble. Concentrated HNO₃ passivates certain metals (like Cu), but 50% HNO₃ is moderately concentrated. **Step 2: Analyze each sulphide** - **HgS**: Extremely insoluble (Ksp ≈ 10⁻⁵³). Does NOT dissolve. ✗ - **PbS**: Moderately insoluble (Ksp ≈ 10⁻²⁸). Dissolves in dilute HNO₃. ✓ - **CuS**: Very insoluble (Ksp ≈ 10⁻³⁶). Does NOT dissolve in 50% HNO₃ (passivation of Cu). ✗ - **Sb₂S₃**: Moderately soluble. Dissolves in HNO₃. ✓ - **As₂S₃**: Moderately soluble. Dissolves in HNO₃. ✓ - **CdS**: Moderately insoluble but dissolves in HNO₃ (Cd is oxidizable). ✓ **Step 3: Count soluble sulphides** Soluble sulphides: PbS, Sb₂S₃, As₂S₃, CdS = 4 sulphides Therefore, the answer is **4.00**.