[akacobee]

Hi all. I am working on a general chem "weak acid titration" and I have ran into an issue. When finding the molar mass of a diprotic acid in titration with NaOH, is the moles of OH- the same as the moles of H+ at the equivalence point? Here the equilibrium equations a classmate and I put together:

H₂A + H₂O  HA + H₃O⁺
HA + H₂O  A^2- + H₃O⁺

The first equation is Ka₁ and the second is Ka₂. One student recommended that we divide the moles of OH- to find the moles of H+. But when I did this method, my experimental molar mass was completely off the charts and wasn't close to any of the given theoretical diprotic acids. But when I calculate the molar mass with the moles of H+ being the same as OH-, I get a pretty decent experimental molar mass and I found what the unknown could be from the given diprotic acids.

I'm guessing I'm asking if I am using the right method to find the molar mass of the diprotic acid. Thanks!

[AWK]

Diprotic acid may react with 1 or 2 moles NaOH, depending on which equivalence point you are using in titration (indicator).