How would you calculate the pH of a mixture here?

Question

Calculate the pH of a mixture containing equal volumes of
0.120 M HC3H5O2 ( use Ka = 1.30 x 10 -5 ) and 0.120 M NaC3H5O2 .

any help would be greatly appreciaTEd!

Answer 1

pH=4.89
pH=pKa+log(A-/Ha)
pH=-log(1.3*10-5)+log(0.120/.120)

Answer 2

What do you mean "equal volumes"? Do you mean 0.120 M HC3H5O2 and 0.120 M NaC3H5O2 in the same volume, or 0.120 M HC3H5O2 in one volume and 0.120 M NaC3H5O2 in the other and you mix the two volumes?
HC3H5O2 <==> H+ + C3H5O2-
Ka = 1.30 x 10 -5 = [H+]* [C3H5O2-] /[HC3H5O2] = [H+]
Hence pH = -log([H+]) = -log(Ka) = 4.89