Chemistry / Unit 2 Chem 0261 worked example, 60 to 90 seconds
Determining Empirical Formula from Molecular Formula
The idea
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.
In practice
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.
Where people slip
Stopping after dividing only one subscript, instead of every subscript by the same number, produces a ratio that no longer matches the original molecule's actual atom counts.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
Unlocks
- Nothing yet depends on this.
Something wrong in this lesson? Flag it · Sources for Chemistry