ACID BASE TITRATION HELP! A 5 g quantity of a diprotic acid was dissolved in water?

"Diprotic" means an acid such as sulfuric which has two available protons per molecule. We are given that 11.1 millimoles of base were used to neutralize; had the acid been monoprotic, half of this (5.55 millimoles) would have sufficed. So, there are 5.55 millimoles of acid used to neutralize 0.5 grams of the acid. Dividing this out, we get 0.5/5.55 = 90 grams per mole. Subtracting off the weight of the protons, we have 88; a possible candidate is C2O4, or HOCOCOOH for the final product.