when a mixture of aluminium powder and iron (III) oxide is ignited, it produces molten iron and aluminium oxide. In an experiment, 5.4gm of aluminium was mixed with 18.5 gm of iron oxide. At the end of the reaction, the mixture contained 11.2 gm of iron, 10.2 gm of aluminium oxide and an undetermined amount of unreacted iron (III) oxide. No aluminium was left. What is the mass of the iron (III) oxide left?