On passing `H_(2)S` gas through a highly acidic solution containing `Cd^(2+)` ions, CdS is not precipitated because

Options

A. Of common ion effect
B. The solubility of CdS is low
C. `Cd^(2+)` ions do not form complex with `H_(2)S`
D. The solubility product of CdS is low

Answer

To understand why CdS is not precipitated when H₂S gas is passed through a highly acidic solution containing Cd²⁺ ions, we can break down the explanation step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
When H₂S is introduced into the solution, it dissociates to produce H⁺ ions and S²⁻ ions:
\[ H_2S \rightleftharpoons 2H^+ + S^{2-} \]

2. **Presence of Cadmium Ions**:
The solution contains cadmium ions (Cd²⁺). Under normal circumstances, if the concentration of S²⁻ ions is sufficient, cadmium sulfide (CdS) can precipitate:
\[ Cd^{2+} + S^{2-} \rightarrow CdS (s) \]

3. **Solubility Product (Ksp)**:
The solubility product (Ksp) of CdS is a constant at a given temperature. For precipitation to occur, the product of the concentrations of Cd²⁺ and S²⁻ must exceed the Ksp:
\[ K_{sp} = [Cd^{2+}][S^{2-}] \]

4. **Effect of Adding H₂S**:
When H₂S is bubbled through the solution, it increases the concentration of S²⁻ ions. However, because the solution is highly acidic, the concentration of H⁺ ions is also high.

5. **Common Ion Effect**:
The increase in S²⁻ ions from H₂S leads to a shift in the equilibrium of the dissolution of CdS. The presence of S²⁻ acts as a common ion, which suppresses the dissociation of CdS due to the common ion effect:
\[ CdS (s) \rightleftharpoons Cd^{2+} + S^{2-} \]
The common ion effect states that the solubility of a salt is reduced in the presence of a common ion.

6. **Conclusion**:
Due to the common ion effect, the increased concentration of S²⁻ ions prevents the precipitation of CdS, as the equilibrium shifts to favor the dissolved ions rather than the solid precipitate. Therefore, CdS does not precipitate in this highly acidic solution.

### Final Answer:
CdS is not precipitated because of the common ion effect caused by the increased concentration of S²⁻ ions from H₂S in the highly acidic solution.

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