.0900g of unknown acid(diproctic acid) with empirical formular(CHO2) is dissolved in 30.0ml of water and the rest is titrated to the endpoint with 50.0ml of .040 M NaOH(aq) determine the molecular formula of the acid?

Answer 1

H2A + 2NaOH ==> 2H2O + Na2A
The rest of what is titrated? I'm assuming you titrated all of it.
mols NaOH = M x L
mols acid = 1/2 mols of NaOH (look at the coefficients in the balanced equation).
mols acid = grams/molar mass. You know mols and grams, solve for molar mass.

Then (empirical mass)*n = molar mass
Solve for n and round to the nearest whole number. Then (empirical formula)_n = molecular formula.