The two ores of iron are hematite and magnetite with the chemical formula Fe2O3 and Fe3O4 respectively. To determine which of the compounds has a higher percentage of iron per kilogram first the molar mass of the two compounds has to be determined.
Iron has a molar mass of 55.845 g/mole and oxygen has a molar mass of 16 g/mole. The molar mass of Fe2O3 is 159.69 and that of Fe3O4 is 231.535. In hematite the percentage of iron by mass is `111.69/159.69 ~~ 69.9%` , similarly in magnetite the percentage of iron by mass is approximately 72.3%
Magnetite has a higher percentage of iron per kilogram as compared to hematite.