Calculating Molecular formulas

Question

1. A compound of iron and iodine has an empirical formula of FeI₃. Its molecular mass is 436.5 g/mol. Determine its molecular formula.

Answer 1

Hello. Here is how we can determine the molecular formula of a compound when given the empirical formula and the molecular mass:

The thing to do is divide the molecular mass by the mass of the empirical formula.

(molecular mass) / (empirical mass)

In this case, the mass of the empirical formula (FeI₃) is 436.5 g/mol, the same as the molecular mass. When the mass of the empirical formula is the same as the molecular mass, the molecular formula is the same as the empirical formula.