Problem 1: A saturated aqueous solution of magnesium methanoate, Mg(HCOO)2, has a solubility of approximately 150 g dm-3 at room temperature. Its exact solubility can be determined by titrating magnesium methanote against aqueous potassium manganate (VII).
During the titration, the methanoate ion, HCOO-, is oxidizes to carbon dioxide while the manganate (VII) ion, MnO4-, is reduced to Mn2+.
You are supplied with
A saturated aqueous solution of Mg(HCOO)2
Aqueous potassium manganate (VII), KMnO4, of concentration 0.0200 mol dm-3
(a) (i). write the half equations for the oxidation of HCOO-(aq) to CO2(g) and the reduction of MnO4-(aq) to Mn2+ (aq) in acid solution.
(ii) Using the approximately solubility above, calculate the concentration, in mol dm-3, of the saturated aqueous magnesium methanoate and the concentration of the methanoate ions present in this solution
(Ai: H, 1.0, C, 12.0, O, 16.0, Mg, 24.3)
(iii) In order to obtain a reliable titre value, the saturated solution of magnesium methanoate needs to be diluted.
Describe how you would accurately measure a 5.0cm3 sample of saturated magnesium methanate solution and use it to prepare a solution fifty times more dilute than the saturated solution.
(vi) 1 mol of acidified MnO4- ions reacts with 2.5 mol of HCOO- ions.
25.0 cm3 of the diluted solution prepared in (iii) required 25.5 cm3 of 0.0200 mol dm-3 potassium manganate (VII) solution to reach the end point.
Use this information to calculate the concentration, in mol dm-3, of HCOO- ions in the diluted solution.