An iron ore (known to contain a mixture of Fe2O3 and Fe3O4) was analyzed by dissolving a 1.1324 g sample in concentrated HCl. The resulting solution was diluted with water, and the iron (III) was precipitated as the hydrous oxide Fe2O3·xH2O by the addition of NH3. After filtration and washing, the residue was ignited at a high temperature to give 0.5394 g of pure Fe2O3. Calculate (a) %Fe and (b) %Fe3O4 in the sample.
(atomic mass: Fe=55.85, O=16)