Question

Be sure to answer all parts. Calculate the concentrations of H2C2O4, HC2O4?, C2O42?, and H+ ions in a 0.227 M oxalic acid solution at 25°C. (Ka1 = 6.5 × 10?2 and Ka2 = 6.1 × 10?5 for oxalic acid.)

[H2C2O4] = M

[HC2O4?] = M

[C2O42?] = M (scientific notation)

[H+] = M

Answer 1

Oxalic acid is diprotic acid

[H2C2O4] = 0.227 M

H2C2O4 + H2O <==> HC2O4- + H3O+

let x amount dissociated

Ka1 = [HC2O4-][H3O+]/[H2C2O4]

6.5 x 10^-2 = x^2/(0.227 - x)

x^2 + 6.5 x 10^-2x - 0.015 = 0

x = 0.0942 M

[H+] = 0.0942 M

[H2C2O4] = 0.227 - 0.0942 = 0.1328 M

HC2O4- + H2O <==> C2O4^2- + H3O+

let x amount dissociated

Ka2 = [C2O4^2-][H3O+]/[HC2O4-]

6.1 x 10^-5 = x^2/0.0942

x = 2.4 x 10^-3 M

[HC2O4-] = 0.0942 - 2.4 x 10^-3 = 0.0918 M

[C2O4^2-] = 2.4 x 10^-3 M