Which solid is less soluble in 0.5 M HCI than in water?

Options

A. `ZnCO_(3)`
B. `Hg_(2)CI_(2)`
C. `PbBr_(2)`
D. `AgI`

Answer

To determine which solid is less soluble in 0.5 M HCl than in water, we need to consider the common ion effect and how it influences solubility. Let's analyze the given options step-by-step.

### Step 1: Understand the Common Ion Effect
The common ion effect states that the solubility of a salt decreases in a solution that already contains one of its constituent ions. This is due to Le Chatelier's principle, which states that if a system at equilibrium is disturbed, the system will shift in a direction that counteracts the disturbance.

### Step 2: Analyze Each Option
1. **Zinc Carbonate (ZnCO3)**: When dissolved in water, it dissociates into Zn²⁺ and CO3²⁻ ions. There are no common ions from HCl, so its solubility is not significantly affected by HCl.

2. **Mercury(I) Chloride (Hg2Cl2)**: This compound dissociates into Hg2²⁺ and Cl⁻ ions. HCl also produces Cl⁻ ions. The presence of Cl⁻ from HCl will decrease the solubility of Hg2Cl2 due to the common ion effect.

3. **Lead Bromide (PbBr2)**: This compound dissociates into Pb²⁺ and Br⁻ ions. There are no common ions from HCl, so its solubility remains unaffected.

4. **Silver Iodide (AgI)**: This compound dissociates into Ag⁺ and I⁻ ions. There are no common ions from HCl, so its solubility remains unaffected.

### Step 3: Conclusion
Among the options, **Mercury(I) Chloride (Hg2Cl2)** is the solid that is less soluble in 0.5 M HCl than in water due to the common ion effect from the Cl⁻ ions present in HCl.

### Final Answer
**Mercury(I) Chloride (Hg2Cl2)** is less soluble in 0.5 M HCl than in water.

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