In which one of the following ways would the pH value of aqueous ammonia be effected by dissolving solid ammonium chloride in it ?

Options

A. Decreases
B. Increases
C. No effect
D. Impossible to predict

Answer

To determine how the pH value of aqueous ammonia is affected by dissolving solid ammonium chloride (NH4Cl) in it, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Components**:
- Aqueous ammonia (NH3) is a weak base.
- Ammonium chloride (NH4Cl) is a salt that dissociates in water to form NH4+ (ammonium ion) and Cl- (chloride ion).

2. **Dissociation of Ammonium Chloride**:
- When NH4Cl is added to the ammonia solution, it dissociates into NH4+ and Cl- ions:
\[ NH4Cl \rightarrow NH4^+ + Cl^- \]

3. **Effect of NH4+ on pH**:
- The NH4+ ion is the conjugate acid of ammonia (NH3). When NH4+ is present in the solution, it can donate protons (H+) to the solution:
\[ NH4^+ \rightleftharpoons NH3 + H^+ \]
- This equilibrium indicates that the addition of NH4+ will increase the concentration of H+ ions in the solution.

4. **Impact on pH**:
- The pH of a solution is inversely related to the concentration of H+ ions. As the concentration of H+ ions increases, the pH of the solution decreases.
- Therefore, the addition of NH4Cl will lead to an increase in H+ concentration, resulting in a decrease in pH.

5. **Conclusion**:
- The overall effect of dissolving solid ammonium chloride in aqueous ammonia is that the pH value will decrease.

### Final Answer:
The pH value of aqueous ammonia will **decrease** upon dissolving solid ammonium chloride in it.

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