Final answer:
When a weak acid's concentration equals that of its conjugate base, the Henderson-Hasselbalch equation simplifies to pH = pKa, indicating that the pH is equal to the pKa of the weak acid when the concentrations are equimolar.
Step-by-step explanation:
When the concentration of a weak acid equals the concentration of its conjugate base, using the Henderson-Hasselbalch equation, the pH of the solution can be calculated using the formula pH = pKa + log([A-]/[HA]). However, if [A-]=[HA], the log([A-]/[HA]) term becomes log(1), which is zero. Therefore, under these conditions, the pH simplifies to pH = pKa.
The Henderson-Hasselbalch equation is a useful tool for understanding buffer solutions and it indicates that when the concentrations of the acid and the conjugate base are equal, the pH is solely determined by the acid's dissociation constant (pKa), making the preparation of buffer solutions at a desired pH more straightforward. The significance of this factor is how it affects the hydrogen ion concentration ([H+]) in a buffer solution and shows the stabilization effect of buffers when adding strong acids or bases to the solution.