Percent Composition Determine the mass percentage of each element in the compound. Determine the mass percentage of each element in the compound. Mass of element x 100% mass of compound mass of compound What is the percent composition of Fe 2 O 3 ? 2 Fe 2 x 55.8 = O 3 x 16.0 = 48.0 Formula mass %Fe = 111.6/159.6 = 70.0% % O = 48.0/159.6 = 30.0%

Empirical formula Gives the lowest whole number ratio of elements in a compound Gives the lowest whole number ratio of elements in a compound The empirical formula for C 6 H 12 O 6 is CH 2 O The empirical formula for C 2 H 6 is CH 3

Calculating Molecular Formula X (empirical formula) = molecular formula so x = molecular formula mass so x = molecular formula mass empirical formula mass empirical formula mass

What is the molecular formula of the molecule that has an empirical formula of CH 2 O and a molar mass of g/mol? What is the molecular formula of the molecule that has an empirical formula of CH 2 O and a molar mass of g/mol? Empirical formula mass: = 30.0 amu X = amu = amu 30.0 amu So C 4 H 8 O 4 is the molecular formula.

Determining empirical formula Find the empirical formula of a compound that contains 53.7% iron and 46.3% sulfur. Find the empirical formula of a compound that contains 53.7% iron and 46.3% sulfur. % composition  mass of 100 g sample  moles  mole ratio % composition  mass of 100 g sample  moles  mole ratio 53.7g x 1 mol/55.8g =.962 mol Fe 53.7g x 1 mol/55.8g =.962 mol Fe 46.3g x 1 mol/32.1g = 1.44 mol S 46.3g x 1 mol/32.1g = 1.44 mol S.962/.962 = 1, 1.44/.962 = /.962 = 1, 1.44/.962 = 1.5 1:1.5 ratio x 2 = 2:3 ratio 1:1.5 ratio x 2 = 2:3 ratio Fe 2 S 3 Fe 2 S 3