Question

Identify the correct order of solubility in aqueous medium :

• A. ${ Na2S > ZnS > CuS }$
• B. ${ CuS > ZnS > Na2S }$
• C. ${ZnS > Na2S > CuS }$
• D. ${Na2S < CuS > ZnS}$

Answer 1

The Correct Option is A

 To determine the correct order of solubility for the compounds \( Na_2S \), \( ZnS \), and \( CuS \) in an aqueous medium, we need to consider their solubility product constants (\( K_{sp} \)). Solubility product constants provide a measure of how much of the substance can dissolve in water at equilibrium.

1. Sodium Sulfide (\( Na_2S \)): Sodium sulfide is a highly soluble salt in water. It dissociates completely to give sodium ions and sulfide ions. Ionic compounds composed of alkali metals and sulfides generally have high solubility in water. Hence, \( Na_2S \) is highly soluble.
2. Zinc Sulfide (\( ZnS \)): Zinc sulfide is known to have low solubility in water. Its solubility is governed by the solubility product constant, which is quite low compared to typical soluble salts, making it sparingly soluble.
3. Copper Sulfide (\( CuS \)): Copper sulfide is even less soluble in water than zinc sulfide. The solubility product constant for \( CuS \) is particularly low, indicating that it is practically insoluble in water at room temperature.

From the above analysis, the decreasing order of solubility is as follows:

\({ Na_2S > ZnS > CuS }\)

This is option 1 from the given choices. The correct answer is:

\({ Na_2S > ZnS > CuS }\)

Conclusion: Sodium sulfide is soluble while both zinc sulfide and copper sulfide have very low solubility, with copper sulfide being the least soluble. This leads us to the correct order.