Unit 8 Chemical 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 Cr: 52.00 g Cr: 104.00 g

% 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 C3H8: 3 (12.01) + 8 (1.01) = 44.11 g/mol % 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

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

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 stinky compound present in rotting meat. 67.4% C 58.8% C 51.7% C 68.2% C % C = 60.05 g C x 100 = 102.21 g total