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Lesson 3: Percent Composition

Lesson 3: Percent Composition. Unit 8 – Moles and Stoichiometry.

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Lesson 3: Percent Composition

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  1. Lesson 3:Percent Composition Unit 8 – Moles and Stoichiometry

  2. Chemists are often involved in developing new compounds for industrial, pharmaceutical, and home uses.After a synthetic chemist (one who makes new compounds) has produced a new compound, an analytical chemist analyzes the compound to provide experimental proof of its composition and chemical formula. Percentage Composition

  3. It is the analytical chemist’s job to identify the elements a compound contains and determine their percent by mass. • Determining the percent of elements in a compound is accomplished in the same way that grades are determined. • How do you calculate a percent? • How do you calculate your grade? Percentage Composition

  4. Percentage Composition • The mass of each element in a compound compared to the entire mass of the compound at 100 percent. • Can be determined 2 ways: 1. Percentage Composition Experimental 2. Theoretical Percentage Composition

  5. Percentage CompositionExperimentally • Activity: Determine the % Composition of sugar in a newly developed gum

  6. Percentage Composition Experimental • Experimental Analysis • Mass of sample measured • Sample is decomposed • Masses of each decomposed element is measured

  7. Theoretical Percentage Composition • From a given formula

  8. 127.10 g Cu 159.16 g Cu2S 32.06 g S 159.16 g Cu2S Percentage Composition Problem • Find the % composition of each element in Cu2S.  100 = %Cu = 79.86% Cu %S =  100 = 20.14% S

  9. 28 g 36 g 8.0 g 36 g Percentage Composition Problems • Find the percentage composition of a sample that is 28 g Fe and 8.0 gO.  100 = 78% Fe %Fe =  100 = 22% O %O =

  10. Percentage Composition Problem • How many grams of copper are in a 38.0-gram sample of Cu2S? Cu2S is 79.852% Cu 30.3 g Cu (38.0 g Cu2S)(0.79852) =

  11. 36.04 g 147.02 g Percentage Composition Problem • Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O? 24.51% H2O %H2O =  100 =

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