An analytical chemist weighs out 0.225g of an unknown diprotic acid into a 250mL volumetric flask and dilutes to the mark with distilled water. He then titrates this solution with 0.0700M NaOHsolution. When the titration reaches the equivalence point, the chemist finds he has added 38.7mL of NaOH solution. Calculate the molar mass of the unknown acid.

1 answer

H2A + 2NaOH ==> Na2A + 2H2O

mols NaOH = M x L = ?
mols H2A must be 1/2 that (look at the coefficients).
mols H2A = grams/molar mass. You know mols and grams, solve for molar mass.