Question

The leaves of the rhubarb plant contain high concentration of diprotic oxalic acid (HOOCCOOH) and must be removed before the stems are used to make the rhubarb pie. If pKa1=1.23 and pKa2=4.19, what is the pH of a 0.0330 M solution of oxalic acid?

Answer 1

concentration of oxalic acid =0.0330 M

pKa1 = 1.23

Ka = 10^-pKa = 0.0589

HOOCCOOH   ---------------------> H + HOOCCOO-

   0.0330                                         0             0

0.0330 - x                                      x               x

Ka1 = x^2 / 0.0330 - x

0.0589 = x^2 / 0.0330 - x

x = 0.024

[H+] = 0.024 M

pH = -log[H+] = -log (0.024)

      = 1.62

pH = 1.62