I am given the following information:

Question

Lactic acid................0.025M...................pH 2.74

How do I calculate the pKa? I don't know how to do it without the concentration. Help please!

Answer 1

dissociation: lactic acid>>>H+ + act-

ka= x*x/(.025-x)
but you know x=10^-2.74=.001819
ka= .001819^2/(.025-.001819)=.001819^2/0.023181= 0.000142735904=10^-3.85

pKa= 3.85
check my math

Answer 2

Thank you so much!!!