The molar mass of Al2O3 is 101.96128 grams per mole with a standard error of plus or minus 0.0009 grams per mole. The atomic weight of each atom of aluminum is 26.98 grams per mole, and the atomic weight of each atom of oxygen is 15.99 grams per mole.
The molar mass is determined by combining the atomic weight of each atom in the compound. As there are two atoms of aluminum, that element contributes a total of 52.96 grams per mole to the total molar mass. The three oxygen atoms contribute a total of 47.99 grams per mole to the total molar mass.