Question

How do you predict the pH of a buffer solution using the Henderson-hasselbalch equation?

Answer 1

It should be fairly close to the `pK_a` of the weak acid used in the buffer.

Explanation:

See this old answer. For the weak acid `HA` mixed with appreciable quantities of its conjugate base:

`pH=pK_a+log_10{([A^-])/([HA])}`

Clearly, when `[A^-]=[HA]`, then `pH=pK_a`. Why so? The `pH` at the point of half-equivalence is therefore used to measure `pK_a`.