Oxalic acid is a relatively strong diprotic acid with Ka1 = 5.6 ´ 10-2 and Ka2 = 5.1 ´ 10-5.
What is the C2O42- concentration in a solution that is 0.10 M in oxalic acid and 1.0 M in HCl? (Consider that the oxalic acid concentration at equilibrium for this common ion problem is 0.10 M.)