pH of which solution is not affected by dilution ?

Options

A. 0.01 M `CH_(3) COONH_(4)`
B. 0.01 M `CH_(3)COONa`
C. A mixture of 00.1 M `CH_(3)COOH+ 0.01M CH_(3) COONa`
D. 0.01 M `NH_(4)Cl`

Answer

To determine which solution's pH is not affected by dilution, we need to analyze the given options based on their properties as acids or bases. Let's break down the solutions step by step.

### Step 1: Analyze Each Solution

1. **0.01 M CH₃COONH₄ (Ammonium Acetate)**:
- This salt is formed from a weak acid (acetic acid, CH₃COOH) and a weak base (ammonium hydroxide, NH₄OH).
- The pH is determined by the equilibrium of the weak acid and weak base. The concentration of H⁺ ions can be calculated using the formula:
\[ [H^+] = \sqrt{\frac{K_a \cdot K_w}{K_b}} \]
- Since this expression does not depend on the concentration of the solution, the pH will not change with dilution.

2. **0.01 M CH₃COONa (Sodium Acetate)**:
- This salt is formed from a weak acid (acetic acid, CH₃COOH) and a strong base (sodium hydroxide, NaOH).
- The pH is determined by the concentration of OH⁻ ions, which can be calculated as:
\[ [OH^-] = \sqrt{K_h \cdot C} \]
- Here, the pH depends on the concentration of the solution, so it will change with dilution.

3. **Mixture of 0.01 M CH₃COOH (Acetic Acid) + 0.01 M CH₃COONa (Sodium Acetate)**:
- This is an acidic buffer solution consisting of a weak acid and its conjugate base.
- Buffers resist changes in pH upon dilution because they maintain a constant ratio of acid to conjugate base.
- Therefore, the pH of this solution will also remain relatively constant upon dilution.

4. **0.01 M NH₄Cl (Ammonium Chloride)**:
- This salt is formed from a weak base (ammonium hydroxide, NH₄OH) and a strong acid (HCl).
- The pH is determined by the concentration of H⁺ ions, which can be calculated as:
\[ [H^+] = \sqrt{K_H \cdot C} \]
- This pH will also change with dilution since it depends on concentration.

### Conclusion:
From the analysis, we find that the pH of the following solutions is not affected by dilution:
- **0.01 M CH₃COONH₄ (Ammonium Acetate)**
- **Mixture of 0.01 M CH₃COOH + 0.01 M CH₃COONa (Acidic Buffer)**

Thus, the correct answers are **Option A (0.01 M CH₃COONH₄)** and **Option C (Mixture of CH₃COOH and CH₃COONa)**.