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# Scan_Doc0100 - 5.15 hydrogen 28.87 nitrogen and 16.49...

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96 Chapter Three Stoichiometry EXAMPLE 3.12 Computer-generated molecule of caffeine. Now we can compute moles .of atoms present per mole of compound: Chlorine: 70.90 g-et 1 mol Cl 2.000 mol Cl X - mol compound 35.45 g-et mol compound Carbon: 24.02g-C 1 mol C 2.000 mol C X mol compound 12.01 g-C mol compound 4.03 g-H 1 molH 4.00 mol H Hydrogen: X mol compound 1.008 g-H mol compound Thus 1 mole of the compound contains 2 mol Cl atoms, 2 mol' C atoms, and 4 mol H atoms, and the molecular formula is C1 2 C 2 H 4 , as obtained in Example 3.10. PROBLEM-SOLVING STRATEGY Determining Molecular Formula from Mass Percent and Molar Mass Using the mass percentages and the molar mass, determine the mass of each element present in one mole of compound. Determine the number of moles of each element present in one mole of compound. • The integers from the previous step represent the subscripts in the molecular formula. Caffeine, a stimulant found in coffee, tea, and chocolate, contains 49.48% carbon,
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Unformatted text preview: 5.15% hydrogen, 28.87% nitrogen, and 16.49% oxygen by mass and has a molar mass of 194.2 g/mol. Determine the molecular formula of caffeine. Solution Where are we going? • To find the molecular formula for caffeine What do we know? .I Percent of each element .I 28.87% N .I 16.49% .I 49.48% C .I 5.15% H .I Molar mass of caffeine is 194.2 g/mol What information do we need to find the molecular formula? .I Mass of each element (in 1 mol caffeine) .I Mole of each element (in 1 mol caffeine) How do we get there? What is the mass of each element in 1 mol (194.2 g) of caffeine? 49.48 g C 194.2 g 96.09 g C X = 100.0 g caffeine mol mol caffeine 5.15 g H 194.2 g 10.0 g H X = 100.0 g caffeine mol mol caffeine 28.87 g N 194.2 g 56.07 g N X = 100.0 g caffeine mol mol caffeine 16.49 g 0 194.2 g 32.02 g X = 100.0 g caffeine mol mol caffeine...
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## This note was uploaded on 12/13/2010 for the course CHEM 2301 taught by Professor Bill during the Spring '10 term at South Texas College.

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