calculating the Ka value for lactic acid.?

Lactic acid, HC3H5O3, builds up in human muscles during anaerobic exercise. If the initial concentration of lactic acid is 0.12 M and the pH is 2.39, calculate the Ka value for lactic acid.

hcbiochem2021-04-08T04:10:49Z

HLa <--> H+ + La-

Ka = [H+][La-]/[HLa] 

From the pH, [H+] = 10^-2.39 = 4.07X10^-3
[H+] = [La-]

Ka = (4.07X10^-3)^2 / 0.12 = 1.4X10^-4