At equilibrium , if to a saturated solution of NaCl, HCl is passed , NaCl gets precipitated because

Options

A. HCl is a strong acid
B. Solubility of NaCl decreases
C. Ionic product of NaCl becomes greater than its `K_("sp")`
D. HCl is a weak acid

Answer

To solve the question of why NaCl precipitates when HCl is passed into a saturated solution of NaCl, we can break down the reasoning into several steps:

### Step-by-Step Solution:

1. **Understanding Saturated Solutions**:
- A saturated solution of NaCl contains Na⁺ and Cl⁻ ions in equilibrium with solid NaCl. At this point, the ionic product (Q) is equal to the solubility product (Ksp) of NaCl.

2. **Dissociation of NaCl**:
- When NaCl is dissolved in water, it dissociates into Na⁺ and Cl⁻ ions:
\[ \text{NaCl (s)} \rightleftharpoons \text{Na}^+ (aq) + \text{Cl}^- (aq) \]

3. **Adding HCl to the Solution**:
- When HCl, a strong acid, is added to the solution, it dissociates completely into H⁺ and Cl⁻ ions:
\[ \text{HCl (aq)} \rightleftharpoons \text{H}^+ (aq) + \text{Cl}^- (aq) \]

4. **Common Ion Effect**:
- The addition of HCl increases the concentration of Cl⁻ ions in the solution. This is known as the common ion effect, which states that the solubility of a salt decreases in the presence of a common ion.

5. **Effect on Ionic Product**:
- With the increase in Cl⁻ concentration, the ionic product (Q) of NaCl increases:
\[ Q = [\text{Na}^+][\text{Cl}^-] \]
- Since the concentration of Cl⁻ has increased, Q becomes greater than Ksp.

6. **Precipitation of NaCl**:
- When Q exceeds Ksp, the solution can no longer hold all the dissolved ions in solution, leading to the precipitation of NaCl:
\[ \text{Na}^+ (aq) + \text{Cl}^- (aq) \rightleftharpoons \text{NaCl (s)} \]

7. **Conclusion**:
- Therefore, the reason NaCl precipitates when HCl is added to a saturated solution of NaCl is due to the common ion effect, which increases the concentration of Cl⁻ ions, resulting in Q exceeding Ksp.