Question

Calculate the pKa  of lactic acid, given that when the concentration of lactic acid is 0.010M and the concentration of lactate is 0.087M, the pH is 4.80.

(a) 4.0

(b) 3.9

(c) 3.3

(d) 4.1

I had been asked this question in an online quiz.

Asked question is from Buffering against pH changes in Biological Systems topic in section Water Basics of Biochemistry

Answer 1

Right option is (b) 3.9

To explain I would say: pH = pKa + log [lactate]/[lactic acid]

pKa = pH – log [lactate]/[lactic acid]

               = 4.80 – log (0.087/0.010) = 4.80 – log 8.7

               = 3.9.