KCET · Chemistry · d and f Block Elements

All Cu(II) halides are known, except the iodide, the reason for it is that

A \(\mathrm{Cu}^{2+}\) oxidises iodide to iodine
B \(\mathrm{Cu}^{2+}\) has much more negative hydration enthalpy
C \(\mathrm{Cu}^{2+}\) ion has smaller size.
D iodide is bulky ion.

Verified Solution

Answer & Solution

Correct Answer

(A) \(\mathrm{Cu}^{2+}\) oxidises iodide to iodine

Step-by-step Solution

Detailed explanation

\(2 \mathrm{Cu}^{2+}+4 \mathrm{I}^{-} \longrightarrow 2 \mathrm{CuI}_2\)
This \(\mathrm{Cu}\) (II) iodide immediately decomposes to liberate \(\mathrm{I}_2\) and insoluble copper (I) iodide.
\[
2 \mathrm{CuI}_2 \longrightarrow 2 \mathrm{CuI}+\mathrm{I}_2
\]

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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