The Henderson-Hasselbalch equation is given by:

[ \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) ]

Where:

• $\text{pH}$ is the pH of the buffer solution.
• $\text{pKa}$ is the dissociation constant of the weak acid.
• $[\text{A}^-]$ is the concentration of the conjugate base.
• $[\text{HA}]$ is the concentration of the weak acid.

To calculate the change in pH after adding 0.1 M HCl or 0.1 M NaOH to the buffer solution, follow these steps:

1. **Determine the initial pH of the buffer