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

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

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

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

Molecular Formula Molecular mass (given)/ empirical mass Example Multiply empirical by the answer Example SNH has a molecular mass of 188.35g/mol, what is the molecular formula? CoC4O4 has molecular mass of 341.94g/mol, what is the molecular formula? 5 5