Question

The molar mass of an organic acid was determined by the following study of its barium salt. 4.290 g of the salt were
to be converted to the free acid by reaction with 21.64 mL of 0.477 M H2SO4. The barium salt was known to contain
2 moles water of hydration per mol Ba2+, and the acid was known to be monoprotic. What is the molar mass of the
anhydrous acid?

Answer 1

Call the organic acid Hox. Then the barium salt will be Ba(ox)2 and since it is a dihydate it will be Ba(ox)2*2H2O.

Ba(ox)2*2H2O + H2SO4 ==> BaSO4 + 2Hox + 2H2O.
mols H2SO4 = M x L = ?
Convert to mols Ba(ox)2*2H2O. That is 1:1 so you have mols
Ba(0x)2*2H2O = mols H2SO4.
Then mols = grams/molar mass. You know grams and mols, solve for molar mass.
Subtract molar mass 2 mols H2O to get molar mass Ba(ox)2.
Subtract atomic mass Ba to get molar mass [(ox)]^2- and add 2*atomic mass H to get 2 mols of the free acid Hox. Divide by 2 to get molar mass of Hox. I did a quick estimate and I think it's approx 120. My guess, although the problem doesn't ask for it, is Hox is benzoic acid. C6H5COOH = molar mass 122. Post your work if you have additional questions.

Answer 2

Thanks a lot for your soln