'Is the amphoteric substance C2O4H- more likely to act as an acid or a base, and why?'

Question

I was given the Ka of C2O4H- as 6.4 x 10^-5, so I calculated its pKa as about 4.19. Then I found its pKb as about 9.80, which makes its Kb about 1.56 x 10^-10. Thus, I concluded that it is more likely to act as an acid because its Ka is higher than its Kb. Am I on the right track here, or am I missing something?

Thanks!

Answer 1

I believe you are on the right track. Here is an excellent example using HCO3^- plus practice problems on the two hydrogen phosphate ions from H3PO4.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch17/either.php