6.00 & of dry pyrolusite containing mainly manganese (IV) oxide was reacted with
12.00 g of ethanedioic acid dihydrate, H, C,0,.2H,0 (an excess) in the presence
of excess sulphuric acid until all the manganese (IV) oxide had reacted. The
insoluble impurities were filtered and the filtrate was made up to 1.00 dm with
distilled water. Manganese (IV) oxide oxidises ethanedioic acid according to the
equation.
MnO(s) + 420,0 (aq) + 2H+ (aq) → Mn2+ (aq) + 24,0(1) + 200, (8)

(a) 25.0 cm of this solution required 22.50 cm' of a 0.0190 mol am potassium
manganate(VII) for complete reaction, according to the equation.
2000, (aq) + 55,0204(aq) + 6*(aq) → Mn2+ (aq) + 10002 (8) + 8H40(1)
Calculate the mass of unreacted H, C,0,.2,0 in the solution.

(b) calculate the mass of HC 0, 1,0 which had reacted with the Mno, present in
the sample of pyrolusite.
Hence calculate the percentage of manganese (IV) oxide in the pyrolusite.