On diluting a buffer solution, its `pH`

Options

A. Increases
B. Decreases
C. Remains same
D. Cannot be predicted

Explanation

To solve the question regarding the effect of dilution on the pH of a buffer solution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Buffer Solutions**:
A buffer solution is a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists changes in pH upon the addition of small amounts of acid or base.

2. **Effect of Dilution**:
When a buffer solution is diluted, the concentrations of both the weak acid and its conjugate base decrease.

3. **Concentration Changes**:
Let's denote the concentration of the weak acid as [HA] and the concentration of the conjugate base as [A-]. Upon dilution, both [HA] and [A-] decrease.

4. **Henderson-Hasselbalch Equation**:
The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation:
\[ \text{pH} = \text{pKa} + \log\left(\frac{[A^-]}{[HA]}\right) \]
Here, pKa is a constant for a given weak acid.

5. **Ratio of Concentrations**:
Since both [HA] and [A-] are diluted equally, their ratio \(\frac{[A^-]}{[HA]}\) remains unchanged.

6. **Conclusion on pH**:
As the ratio \(\frac{[A^-]}{[HA]}\) does not change, the pH calculated using the Henderson-Hasselbalch equation also remains unchanged.

7. **Final Answer**:
Therefore, upon diluting a buffer solution, its pH remains the same.

### Final Answer:
The pH of a buffer solution remains unchanged upon dilution.