Percent Composition It helps to know the % of the components in a shirt because they affect how warm it is, whether it will need to be ironed, and how it should be cleaned. You will learn how the % of the elements in a compound are important in chemistry.

% Composition % by mass = mass of element x 100 total mass 194.20 g/mol 294.20 g/mol

% by mass = mass of element x 100 total mass % O = 5.40 g O x 100 = 13.60 g 39.7 % O % Mg = 8.20 g Mg x 100 = 13.60 g 60.3 % Mg

% by mass = mass of element x 100 total mass % C = 36.03 g C x 100 = 44.11 g 81.68 % C % H = 8.08 g H x 100 = 44.11 g 18.32 % H 3 (12.01) + 8 (1.01) = 44.11 g /mol

17.04 g /mol 80.06 g /mol NH3: %N = 14.01 g N x 100 = 17.04 g 82.22 % N NH4NO3: %N = 28.02 g N x 100 = 80.06 g 35.00 % N

% Composition Calculate the mass of oxygen in 175 g of N2O4. Find the decimal composition of the element. 2(14.01) + 4(16.00) = 92.02 g/mol O = 64.00 = 92.02 0.696 2) Multiply decimal composition by total mass of the compound. 0.696 x 175g = 122 g of O

% Composition Calculate the mass of aluminum in 425 g of Al2(SO4)3. 2(26.98) + 3(32.07) + 12(16.00) = 342.17 g/mol Al = 53.96 = 342.17 0.158 0.158 x 425 g = 67.2 g Al

% Composition Calculate the mass of carbon in a compound containing 92.2% C with a mass of 125 g. 0.922 x 125 = 115 g C

Quick Quiz! 1. The percent composition of a compound is found by dividing the mass of each element by the ________. moles of each element percent of each element total mass of the compound total number of elements

Quick Quiz. Calculate the percent by mass of carbon in cadaverine, C5H14N2, a compound present in rotting meat. 67.4% C 58.8% C 51.7% C 68.2% C