When a buffer solution of `CH_(3)COOH` and `CH_(3)COONa`is diluted with water

Options

A. `CH_(3)COO^(-)`ion concentration increases
B. `H^(+)`ion concentration increases
C. `OH^(-)`ion concentration increases
D. `H^(+)`ion concentration does not change

Answer

### Step-by-Step Solution:

1. **Understanding the Components of the Buffer Solution**:
- The buffer solution consists of acetic acid (CH₃COOH) and its conjugate base, sodium acetate (CH₃COONa).
- Acetic acid is a weak acid, and sodium acetate is its salt, which provides acetate ions (CH₃COO⁻) in solution.

2. **Definition of a Buffer Solution**:
- A buffer solution is designed to resist changes in pH when small amounts of acid or base are added. It does this by maintaining a balance between the weak acid and its conjugate base.

3. **Effect of Dilution on the Buffer Solution**:
- When the buffer solution is diluted with water, the concentrations of both the acetic acid and sodium acetate decrease.
- However, the ratio of the concentrations of the salt (sodium acetate) to the acid (acetic acid) remains constant.

4. **Using the Henderson-Hasselbalch Equation**:
- The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation:
\[ \text{pH} = \text{pKa} + \log\left(\frac{[\text{Salt}]}{[\text{Acid}]}\right) \]
- Since both the concentration of the salt and the acid decrease equally upon dilution, the ratio \(\frac{[\text{Salt}]}{[\text{Acid}]}\) remains unchanged.

5. **Conclusion on H⁺ Ion Concentration**:
- Because the ratio remains constant, the pH of the solution does not change significantly upon dilution.
- Therefore, the concentration of H⁺ ions also remains constant.

6. **Final Answer**:
- The correct option is that the H⁺ ion concentration does not change (remains constant).