1. Percent Composition Percent by mass Element mass/compound mass x 100
NaCl
Ca3(PO4)2 1 1

2. Empirical Formulas Determined by lab data
Can determine molecular formula if you have the mass
Percent to mass
Mass to mole
Divide by small
Multiply till whole
All ionic compounds are empirical
Covalent compounds may or may not be empirical 2 2

3. Empirical Examples Empirical or Molecular? H2O H2O2 CaCl2
Ca3(PO4)2 (Ca3P2O8)
N2O4
NO2 3 3

4. Empirical Practice
56.79% Carbon, 6.56% Hydrogen, 28.37% Oxygen, 8.28% Nitrogen 4 4

5. Molecular Formula Molecular mass (given)/ empirical mass Example
Multiply empirical by the answer
Example
SNH has a molecular mass of g/mol, what is the molecular formula?
CoC4O4 has molecular mass of g/mol, what is the molecular formula? 5 5