Question

What fraction of a 0.5 m acetic acid solution will be in the protonated form at ph 5.1? The pka of acetic acid is 4.8?

Answer 1

The acetic acid will dissociate as

We will use Hendersen Hassalbalch's equation here

pH = pKa + log [salt] / [acid]

Where

[Acid] = concentration of protonated form

5.1 = 4.8 + log [salt] / [acid]

1.99= [salt] / [acid]

[salt] +[acid] = 0.5

1.99 [acid] + [acid] = 0.5

[acid] = 0.167 M

[acid] / total concentration = 0.167 / 0.5 = 0.33.4

So percentage = 33.4 % or approx 33 %