Final answer:
The buffer capacity reaches a maximum when pH = pKa because at this point, the weak acid and its conjugate base are present in equal concentrations. This allows the buffer to effectively resist changes in pH when small amounts of acid or base are added.
Step-by-step explanation:
The buffer capacity reaches a maximum when pH = pKa because at this point, the weak acid and its conjugate base are present in equal concentrations.
This allows the buffer to effectively resist changes in pH when small amounts of acid or base are added.
The Henderson-Hasselbalch Equation, pH = pKa + log([A-]/[HA]), shows that when [A-] = [HA], the log term becomes zero, resulting in a pH equal to pKa.