5.00 g of an impure sample of hydrated ethanedioic acid, (COOH)2•2H2O, was dissolved in water to make 1.00 dm3 of solution. 25.0 cm3 samples of this solution were titrated against a 0.100 mol dm-3 solution of sodium hydroxide using a suitable indicator. (COOH)2 (aq) + 2NaOH (aq) → (COONa)2 (aq) + 2H2O (l)
The mean value of the titre was 14.0 cm3.

(i) Calculate the amount, in mol, of NaOH in 14.0 cm3 of 0.100 mol dm-3 solution.
(ii) Calculate the amount, in mol, of ethanedioic acid in each 25.0 cm3 sample.
(iii) Determine the percentage purity of the hydrated ethanedioic acid sample.