When finding empirical formula of a compound, why do you have to convert the elements into moles, as opposed to using a mass:mass ratio?

Answer 1

The empirical formula is based on moles and not grams.
Al2O3 means 2 molecules of Al have combined with 3 molecules of oxygen. (Multiplying molecules by 6.022 x 10^23 converts each to a ratio of 2 moles to 3 moles. Since Avogadro's number is constant we need not multiply the molecules by that number). As opposed, it is NOT 2 grams Al combined with 3 grams O but 2 molecules of Al combined with 3 molecules of O.