Determining Empirical Formula from Molecular Formula

Determining a compound's empirical formula from its molecular formula means dividing every subscript by the largest whole number that divides all of them evenly.

Acetic acid's molecular formula, C2H4O2, has subscripts 2, 4, and 2. The largest number dividing all three evenly is 2, giving a reduced ratio of 1, 2, 1 — the empirical formula CH2O. Glucose's molecular formula, C6H12O6, divides by 6 the same way, giving the identical empirical formula CH2O, even though glucose and acetic acid are different-sized molecules. Hydrogen peroxide, H2O2, divides by 2 as well, reducing to HO, a formula whose subscripts are already the smallest possible whole numbers.