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# WS3_key - Chem 142 Name Worksheet 3 Stoichiometry Summer...

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Chem 142 Summer 2011 Page 1 of 3 Name ________________________________________ Section ________________ Worksheet 3: Stoichiometry 1. Calculate the average atomic mass of Zirconium (Zr). 90 Zr (51.45%), 91 Zr (11.27%), 92 Zr (17.17%), 94 Zr (17.33%), 96 Zr (2.78%). average atomic mass = 90 amu ! 0.5145 ( ) + 91 amu ! 0.1127 ( ) + 92 amu ! 0.1717 ( ) + 94 amu ! 0.1733 ( ) + 96 amu ! 0.0278 ( ) " # \$ \$ \$ % & = 91.32 amu 2. Sucrose is the common sugar used in all homes, and chemical analysis tells us that the chemical composition is 42.14% carbon, 6.48% hydrogen and 51.46% oxygen. What is the molecular formula of sucrose if its molar mass is approximately 340 g/mol? Assume 100 g of sucrose. moles C = 42.14 g C ! 1 mol C 12.011 g C = 3.508 mol C moles H = 6.48 g H ! 1 mol H 1.008 g H = 6.429 mol H moles O = 51.46 g O ! 1 mol O 16.00 g O = 3.216 mol O empirical formula CH 2 O empirical equivalents = 340 g mol sucrose 30 g mol empirical = 11 molecular formula C 11 H 22 O 11 3. Determine the empirical and molecular formulas for a deadly nerve gas that gives the following mass percent analysis. C = 39.10% H = 7.67% O = 26.11% P = 16.82% F = 10.30% The molar mass is known to be 184.1 g/mol. Assume 100 g of compound.

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