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. Chemical Composition Unit 7

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

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

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

NH 3 : %N = g N x 100 = g 82.22% N NH 4 NO 3 : %N = g N x 100 = g 35.00% N g/mol g/mol

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

2.Calculate the percent by mass of carbon in cadaverine, C 5 H 14 N 2, a stinky compound present in rotting meat. A.67.4% C B.58.8% C C.51.7% C D.68.2% C Quick Quiz.