Besides the empirical formula, what is needed to work out a compound's molecular formula?

1. An empirical formula only fixes the relative numbers of atoms, not the absolute numbers in one molecule. 2. To get the absolute numbers you also need the molecular mass or the molar mass. 3. Dividing that mass by the empirical formula mass gives the number of formula units per molecule. 4. Percent composition is what the empirical formula was derived from, so it adds nothing new here. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.2 Determining Empirical and Molecular Formulas_