Calculating Empirical Formulae So we have 6 mol C, 6 mol H, 1 mol N, and 1.5 mol O Step 3: if each is a whole number, write the empirical formula C 12 H 12 N 2 O 3 What is the empirical formula of a compound that is made up of 62.1% C, 5.21% H, 12.1% N, and 20.7% O.