What is the pH of the buffer?

A buffer consists of a weak acid or base, and the salt of that acid or base.

Consider a buffer made by combining the weak acid HA with its salt, A−:

HA(aq)+H2O(l)⇌A−(aq)+H3O+(aq)

Ka=[A−][H3O+][HA]
The H3O+ concentration of this buffer can be calculated using the Ka expression:

[H3O+]=Ka[HA][A−]
You can use this expression when solving for pH, or you can simplify the expression even more. Taking the negative log of this expression, you have

−log[H3O+]=−log[Ka]−log[HA][A−]
Since −log[H3O+]=pH and −log[Ka]=pKa, this can be further simplified to

pH=pKa+log[A−][HA]



A lactic acid/lactate ion buffer solution contains 0.24M HC3H5O3 and 0.75M C3H5O3−, respectively.
The Ka value of lactic acid is 1.4×10−4.
Calculate the pH of this buffer.