Question

What is the expected pH of a 0.250 M solution of oxalic acid with Ka = 5.37 x 10^-5 ([H+] = 0.002197) and will the pH increase by one unit if the solution is diluted to 0.0250 M?

Answer 1

[H+] = 0.002197 M

pH = -log [H+] = -log (0.002197)

      = 2.66

pH = 2.66

C2H4O2 ---------------> C2H3O2- + H+

0.0250                                   0          0

0.0250-x                                x           x

Ka = x^2 / 0.0250 - x

5.37 x 10^-5 = x^2 / 0.0250 - x

x = 1.132 x 10^-3

[H+] = 1.132 x 10^-3 M

pH = -log [H+] = -log(1.132 x 10^-3)

     = 2.95

pH = 2.95

pH change = 2.95 - 2.66 = 0.29

no , pH will not increase one unit. it only increases 0.29 units