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PERCENT COMPOSITION Section 6.1 SYNTHETIC COMPOUNDS Natural compounds can be produced in a lab for a cheaper price Ex: Vanilla from vanillin (produced chemically in bulk) How is vanillin made in a lab? Determine the elements in the compound Determine the proportion (how much) of each element is present THE LAW OF DEFINITE PROPORTIONS The elements in a chemical compound are always present in the SAME proportions by mass Ex: H2O: the proportion of Hydrogen and Oxygen stays constant MASS PERCENT OF AN ELEMENT Mass of element x 100% Mass of compound MASS PERCENT OF AN ELEMENT Mass percent of hydrogen in water: Mass of H2 = 2 (1.01) = 2.02 g Mass of H2O= 18.02 g/mol (Molar mass) % mass of H2 = mass of H2 mass of H2O = 2.02 g x 100% 18.02 g/mol = 11.2 % PERCENT COMPOSITION Tells you the mass percent (%) of all elements in a molecule PERCENT COMPOSITION Ex 1: A compound with a mass of 48.72 g is found to have 32.69 g of zinc and 16.03g of sulfur. What is the percent composition of the compound? Given: Mass of compound 48.72 g Mass of Zn = 32.69 g Mass of S = 16.03 g PERCENT COMPOSITION % Zn = 32.69g x 100% 48.72g % S = 16.03g x 100% 48.72g = 67.10% = 32.90 % PERCENT COMPOSITION Can also be calculated using the chemical formula Ex 2: What is the % composition of C9H8O? = 9(12.01g/mol) + 8(1.01g/mol) + 16g/mol = 132.17g/mol Mass of carbon= 9(12.01) = 108.09 g/mol Mass of hydrogen = 8(1.01) = 8.08 g/mol Mass of oxygen = 1(16.00) = 16 g/mol PERCENT COMPOSITION % C = 108.09 g x 100% 132.17g = 81.78 % % H = 8.08g x 100% 132.17 g = 6.11 % % O = 16.00g x 100% 132.17 g = 12. 10% POPCORN A bag of popcorn had a mass of 91.6 g before BEING popped and a mass of 80.2 g AFTER popping Find the mass of H2O lost Find the % mass of H2O in popcorn Find the mass of H and O lost when the popcorn was popped a) Mass of H2O lost 91.6 g – 80.2 g = 11.4g b) % mass of H2O %