1. % Composition, Empirical Formulas, & Molecular Formulas

2. % Composition % = (part / whole ) x 100
When calculating the % composition, you are calculating the % of each element in a compound

3. % Composition
Calculate the % Composition of MgO

4. % Composition
Calculate the % Composition of iron (III) oxide

5. Empirical & Molecular Formulas
_______________ – the smallest whole number ratio of elements
_______________ – the true number of elements in a compound

6. Empirical Formula What is the empirical formula for H2O2?
What is the empirical formula for C6H12O6?

7. Steps for Calculating the Empirical Formula
List your givens
Change % to grams
Change grams to moles
Divide everything by the smallest number of moles
Write your formula

8. Empirical Formula Problem
Calculate the empirical formula of a compound containing % S and % O.

9. Empirical Formula Problem
Calculate the empirical formula for a compound containing g C, 8.16 g H, and g O.

10. Steps for Calculating Molecular Formula
Calculate the empirical formula
Get the molecular mass of the empirical formula that you just determined
Divide the experimentally determined molecular mass (given) by the molecular mass of the empirical formula
You will get a whole number
Multiply everything in the empirical formula by this number

11. Molecular Formula Problem
Calculate the molecular formula of a compound containing 40.68%C, 5.08%H, and 54.25%O with an experimentally determined molecular weight of g/mol

12. Molecular Formula Problem
Calculate the molecular formula of a compound containing g C, 3.64 g H, and g O with an experimentally determined molecular mass of g/mol