Purifying mass, iron oxide

Aluminum is the third most abundant element in the earth s crust (after oxygen and silicon), accounting for 8.2% of the total mass. It occurs most commonly in association with silicon in the aluminosilicates of feldspars and micas and in clays, the products of weathering of these rocks. The most important ore for aluminum production is bauxite, a hydrated aluminum oxide that contains 50% to 60% AI2O3 1% to 20% FeiOs 1% to 10% silica minor concentrations of titanium, zirconium, vanadium, and other transition-metal oxides and the balance (20% to 30%) water. Bauxite is purified via the Bayer process, which takes advantage of the fact that the amphoteric oxide alumina is soluble in strong bases but iron(III) oxide is not. Crude bauxite is dissolved in sodium hydroxide... 

Example 4-3. In a determination of the atomic mass of iron, 7.59712 g of carefully purified ferric oxide, Fe>03, was reduced by heating in a stream of hydrogen, and found to yield 5.31364 g of metallic iron. Given the atomic mass of oxygen, to what value of the atomic mass of iron does this result lead ... 

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