Oxalic acid dihydrate is a solid, diprotic acid that can be used in the laboratory as a primary standard. Its formula is H2C2O4•2H2O.

Question

Oxalic acid dihydrate is a solid, diprotic acid that can be used in the laboratory as a primary standard. Its formula is H₂C₂O₄•2H₂O.

A student dissolves 0.851 grams of H₂C₂O₄•2H₂O in water and titrates the resulting solution with a solution of potassium hydroxide of unknown concentration. If 39.1 mL of the potassium hydroxide solution are required to neutralize the acid, what is the molarity of the potassium hydroxide solution?

Answer 1

Look at the reaction between oxalic acid (H₂C₂O₄) and potassium hydroxide (KOH)

H₂C₂O₄ + 2KOH = K₂C₂O₄ + 2H₂O ... balanced equation

molar mass H₂C₂O₄* 2H₂O = 126.1 g / mol

mols H₂C₂O₄* 2H₂O present = 0.851 g x 1 mol / 126.1 g = 0.006749 mols

mols KOH needed for neutralization = 0.006749 mols H₂C₂O₄ x 2 mol KOH / mol H₂C₂O₄ = 0.0135 mols KOH

Molarity of KOH = 0.0135 mols / 39.1 ml x 1000 ml / L = 0.345 mol/L = 0.345 M KOH (3 sig. figs.)