Question

Identify the correct order of solubility in aqueous medium

• A. CuS > ZnS > Na₂S
• B. ZnS > Na₂S > CuS
• C. Na₂S > CuS > ZnS
• D. Na₂S > ZnS > CuS

Answer 1

The Correct Option is D

To determine the correct order of solubility in an aqueous medium among CuS, ZnS, and Na₂S, we need to consider their solubility product constants (K_{sp} values) and the nature of these compounds.

1. Understanding Solubility Products:
   • Solubility is a measure of how much solute can dissolve in a solvent at a given temperature. In this context, it refers to how much of each sulfide compound can dissolve in water.
   • The solubility product constant, K_{sp}, is an equilibrium constant that applies to the solubility of ionic compounds. A higher K_{sp} value indicates higher solubility.
2. Analyzing the Compounds:
   • Na₂S: This is a highly soluble ionic compound. Sodium sulfide readily dissolves in water as it dissociates into Na⁺ and S^2- ions, both of which are very soluble.
   • ZnS: Zinc sulfide is much less soluble than Na₂S but more soluble than CuS. It has a moderate K_{sp} value reflecting its limited solubility.
   • CuS: Copper sulfide is the least soluble among the three. It has a very low K_{sp} value, making it poorly soluble in water.
3. Conclusion:
   • From the analysis above, the correct order of increasing solubility is:
   • Na₂S > ZnS > CuS
   • This order aligns with their individual K_{sp} values and their nature in the aqueous medium.

Therefore, the correct option is: Na₂S > ZnS > CuS.