Question

A lactic acid/lactate ion buffer solution contains 0.37 M HC3H5O3 and 0.66 M C3H5O3− , respectively. The Ka value of lactic acid is 1.4×10−4 . Calculate the pH of this buffer.

Answer 1

Using the Henderson-Hasselbalch equation and the given concentrations of lactic acid and its conjugate base, along with the Ka value, the pH of the buffer solution is calculated to be 4.10.

Step-by-step explanation:

To calculate the pH of a lactic acid/lactate ion buffer solution, we use the Henderson-Hasselbalch equation:

pH = pKa + log(·[conjugate base] ·[conjugate acid])

Here, the concentrations are 0.37 M for lactic acid (HC3H5O3) and 0.66 M for lactate ion (C3H5O3−).

The given Ka value for lactic acid is 1.4×10−4, which gives us a pKa of -log(1.4×10−4).

Firstly, calculate the pKa:

pKa = -log(1.4×10−4)

= 3.85

Now, plug the values into the Henderson-Hasselbalch equation:

pH = 3.85 + log(0.66 · 0.37)

pH = 3.85 + log(1.78)

pH = 3.85 + 0.25

= 4.10

Therefore, the pH of the buffer solution is 4.10.