The molar mass of Fe2O3, which is the chemical formula for iron(III) oxide, is 159.68 grams per mole. The molar mass is determined by adding together the atomic weight of each atom in the compound.
In Fe2O3, the Fe stands for iron and the O stands for oxygen. A single atom of iron has an atomic weight of 55.84 grams per mole, while a single atom of oxygen has an atomic weight of 15.99 grams per mole. The total weight of the two iron atoms in the formula is 111.68 grams per mole, and the total weight of the three atoms of oxygen is 47.97 grams per mole.