Question

Oxalic acid (H2C2O4) is a diprotic acid that occurs in plants such as rhubarb and spinach.

Calculate the pH (part A) and the concentration (part B) of C2O2−4 ions in 0.12 M H2C2O4 (Ka1=5.9×10−2; Ka2=6.4×10−5).

Answer 1

part A)

concnetration of H2C2O4 = 0.12 M

H2C2O4    ------------------> HC2O4-   +   H+

0.12                                         0                0

0.12 - x                                    x                 x

Ka1 = x^2 / 0.12 - x

5.9 x 10^-2 = x^2 / 0.12 - x

x = 0.0597

[H+] = 0.0597 M

pH = -log (0.0597)

pH = 1.22

part B)

[C2O42-] = 6.4 x 10^-5 M