1. Chapter 11 Empirical and Molecular Formulas
Chemistry
Chapter 11
Empirical and Molecular Formulas

2. Empirical Formulas
The simplest whole number ratio of the elements in a compound (not necessarily the actual formula for a compound) Ex
H2O2 = HO
H2O= H2O
C6H12 = CH2
C8H16 = CH2
Can be calculated from % composition

3. Empirical Formula (Cheat Sheet)
1. % composition (if = 100%) converts to
mass
Convert from mass to moles
Calculate simplest ratio
(divide all # mol by the smallest # moles)
3 ½. If not all whole numbers, multiply all
by a whole # to create whole #’s
4. Use simplest ratio as subscripts

4. Examples
11.2 % Hydrogen and 88.8% Oxygen

5. Examples
36.84% N and 63.16% O

6. Examples
60% C, 4.44%H, and 35.56% Oxygen

7. Molecular Formula Actual number of moles of each element in a compound
Need more info than just % comp
Need molar mass of the empirical formula
Need an experimental mass of the actual compound

8. Molecular Formula (Cheat Sheet)
Use steps to calculate empirical formula
Calculate molar mass of empirical formula
The question will give you experimental mass of the compound
Experimental mass
Empirical form. Molar mass =
5. Multiply subscripts in empirical by your answer (whole number)

9. Example
A colorless liquid is found to be composed of 46.68% N and 53.32% O and has a molar mass of g/mol. What is the molecular formula?