COMEDK · Chemistry · 8. Ionic Equilibrium

On passing \(\mathrm{H}_{2} \mathrm{~S}\) into a solution containing both \(\mathrm{Zn}^{2+}\) and \(\mathrm{Cu}^{2+}\) in acidic medium, only CuS gets precipitate(d) This is because

A \(K_{\mathrm{sp}}\) of \(\mathrm{CuS} < K_{\mathrm{sp}}\) of \(\mathrm{ZnS}\)
B \(K_{\mathrm{sp}}\) of \(\mathrm{CuS}=K_{\mathrm{sp}}\) of \(\mathrm{ZnS}\)
C \(K_{s p}\) of CuS \(>K_{\mathrm{sp}}\) of \(\mathrm{ZnS}\)
D CuS is more stable than \(\mathrm{ZnS}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(K_{\mathrm{sp}}\) of \(\mathrm{CuS} < K_{\mathrm{sp}}\) of \(\mathrm{ZnS}\)

Step-by-step Solution

Detailed explanation

On passing \(\mathrm{H}_{2} \mathrm{~S}\) into a solution containing \(\mathrm{Zn}^{2+}\) and \(\mathrm{Cu}^{2+}\) ions, \(\mathrm{ZnS}\) and \(\mathrm{CuS}\) are formed. The solubility product of CuS is less than that of \(\mathrm{ZnS}\). \(\therefore\) CuS get precipitated.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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