Question

Identify 'P' and 'Q' in the following reaction

• A. Option a
• B. Option b
• C. Option c
• D. Option d

Hint:

Coordination chemistry tips:
CN\( ^- \) forms strong complexes
Sulfides of Cd are highly insoluble
H\(_2\)S used for qualitative analysis of metal ions

Answer 1

The Correct Option is A

Concept: Ligand substitution and complex formation: CN\( ^- \) is strong field ligand. Replaces NH\(_3\) in coordination sphere.
Step 1: Formation of P
\[ [\text{Cd(NH}_3)_4]^{2+} + 4\text{CN}^- \rightarrow [\text{Cd(CN)}_4]^{2-} \]
With K\( ^+ \):
\[ P = \text{K}_2[\text{Cd(CN)}_4] \]
Step 2: Reaction with H\(_2\)S
S\( ^{2-} \) forms highly insoluble CdS. Even from complex, Cd\( ^{2+} \) precipitates as CdS:
\[ [\text{Cd(CN)}_4]^{2-} + \text{H}_2\text{S} \rightarrow \text{CdS} \downarrow \]
Conclusion:
\[ P = \text{K}_2[\text{Cd(CN)}_4], \quad Q = \text{CdS} \]