On adding ammonium chloride to a solution ammonium hydroxide

Options

A. Dissociation of `NH_4OH` increases
B. Concentration of OH increases
C. Concentration of OH decreases
D. Concentration of OH remains unchanged

Answer

To solve the question regarding the effect of adding ammonium chloride to a solution of ammonium hydroxide, we will analyze the chemical behavior of both substances involved.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Ammonium hydroxide (NH₄OH) is a weak base that partially dissociates in solution.
- Ammonium chloride (NH₄Cl) is a strong electrolyte that completely dissociates in solution.

2. **Dissociation of Ammonium Hydroxide**:
- The dissociation of ammonium hydroxide can be represented as:
\[ \text{NH}_4\text{OH} \rightleftharpoons \text{NH}_4^+ + \text{OH}^- \]
- This means that when ammonium hydroxide is dissolved in water, it produces ammonium ions (NH₄⁺) and hydroxide ions (OH⁻).

3. **Dissociation of Ammonium Chloride**:
- When ammonium chloride is added to the solution, it dissociates completely:
\[ \text{NH}_4\text{Cl} \rightarrow \text{NH}_4^+ + \text{Cl}^- \]
- This increases the concentration of ammonium ions (NH₄⁺) in the solution.

4. **Common Ion Effect**:
- The addition of ammonium chloride increases the concentration of the ammonium ion (NH₄⁺), which is a common ion in the equilibrium established by ammonium hydroxide.
- According to Le Chatelier's principle, if the concentration of a product in a reversible reaction increases, the equilibrium will shift to the left (backward direction) to counteract this change.

5. **Effect on Hydroxide Ion Concentration**:
- As the equilibrium shifts to the left, the dissociation of ammonium hydroxide decreases, leading to a decrease in the concentration of hydroxide ions (OH⁻).
- Therefore, the concentration of OH⁻ ions will decrease.

6. **Conclusion**:
- Based on the analysis, the correct option is that the concentration of OH⁻ ions decreases when ammonium chloride is added to the solution of ammonium hydroxide.

### Final Answer:
The concentration of OH⁻ ions decreases (Option 3).