Use an acid–base titration to calculate the molar mass of an acid.

Question

A 0.7885-g sample of an unknown monoprotic acid is dissolved in water and titrated with standardized barium hydroxide. The equivalence point in the titration is reached after the addition of 33.11 mL of 0.1122 M barium hydroxide to the sample of the unknown acid. Calculate the molar mass of the acid.

Answer 1

Let the monoprotic acid be HA

2HA + Ba(OH)2 ==> Ba(A)2 + 2H2O ... balanced neutralization reaction

mols Ba(OH)2 needed for neutralization = 0.03311 L x 0.1122 mol/L = 0.037149 mols

mols HA present = 0.037149 mols Ba(OH)2 x 2 mol HA / mol Ba(OH)2 = 0.07430 mols

Molar mass of unknown acid = 0.7885 g / 0.07430 mol = 106.1 g / mole