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Percent Composition

Percent Composition. Law of Definite Proportions. The Law of Definite Proportions states that a compound is always comprised of the same atoms in the same ratio, or percentage. In order to determine the percentages, we use molar mass. Percent Composition.

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Percent Composition

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  1. Percent Composition

  2. Law of Definite Proportions • The Law of Definite Proportions states that a compound is always comprised of the same atoms in the same ratio, or percentage. • In order to determine the percentages, we use molar mass

  3. Percent Composition • Percent composition gives you the ratio of the mass of one element to all the other elements that make up a unique compound. • Methane, CH4, is comprised of 1 atom of carbon and 4 atoms of hydrogen. • The molar mass of methane is 16.04 g/mol • Carbon contributes a total mass of 12.01 g/mol • All Hydrogen atoms together contribute 4.03 g/mol • The ratio of C:CH4 is 12.01:16.04 or 74.88% • The ratio of H:CH4 is 4.03:16.04 or 25.12% • So therefore, the percent composition of methane is 74.88% Carbon and 25.12% Hydrogen

  4. Practice problems • Calculate the % composition of Fe3C, a compound used to cast iron. • Calculate the % composition of sulfur dioxide. • Calculate the % composition of ammonium nitrate. • Calculate the percent composition of glucose, C6H12O6. • Calculate the percent composition of acetic acid, CH3COOH.

  5. Practice problems • Calculate the % composition of Fe3C, a compound used to cast iron. • Fe = 55.85 g/mol x 3 = 167.6 g/mol • C = 12.01 g/mol • Fe3C = 167.6 g/mol + 12.01 g/mol = 179.6 g/mol • % Fe = 167.6 g/mol / 179.6 g/mol x 100 = 93.32% • % C = 12.01 g/mol / 179.6 g/mol x 100 = 6.69%

  6. Practice Problem Answers • 93.32% Fe, 6.69% C • 50.05% S, 49.95% O • 35.00% N, 5.05% H, 59.96% O (p.s. the formula is NH4NO3) • 39.99% C, 6.73% H, 53.28% O • 39.99% C, 6.73% H, 53.28% O !!!! • What is the empirical formula for each?!!!

  7. Homework • Worksheet

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