Let us assume that the given values of each element completely react with each other. To solve for the empirical formula, first we have to calculate for the number of moles of each element.
Molar mass Al = 27 g / mol
Molar mass Oxygen = 16 g / mol
Therefore the number of moles each is:
moles Al = 5 / 27 = 0.185 mol
moles O = 4.45 / 16 = 0.278 mol
Next we divide each moles with the smallest mol value, in this case 0.185 mol, therefore divide the two with 0.185 mol:
moles Al = 0.185 / 0.185 = 1
moles O = 0.278/0.185 = 1.5
The empirical formula must be in whole numbers, however moles O is still in decimal. Therefore multiply the two by 2:
moles Al = 1 * 2 = 2
moles O = 1.5 * 2 = 3
Therefore the empirical formula is:
Al2O3
