Final answer:
When pH is equal to pKa, it signifies the midpoint of a weak acid's titration curve,where the concentration of the acid equals that of its conjugate base and the buffer capacity is at its peak. This relation can be used to determine both the concentration and pKa, utilizing the Henderson-Hasselbalch equation.
Step-by-step explanation:
When pH equals pKa, it indicates that the concentration of the acid (HA) is equal to the concentration of its conjugate base (A-). At this point, the weak acid is exactly half dissociated, making it the midpoint in the titration curve of the weak acid.
This scenario is best described by the Henderson-Hasselbalch equation, relating the pH, the pKa, and the concentrations of a weak acid and its conjugate base in a solution.
The condition where pH is equal to pKa is significant because at this point, the buffer solution has a unique property: the pH remains relatively stable even when small amounts of acid or base are added.
This is the optimal buffering point, also known as the buffer capacity peak. In addition, knowing that pH equals pKa at the midpoint of the titration allows us to use titration methods to determine both the concentration and the pKa of the weak acid.