RecitationSet2_AnsKey

RecitationSet2_AnsKey - Tufts University - Chem 1 - Summer...

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Tufts University - Chem 1 - Summer 2008 Recitation Set 2 Answer Key 1 . Hydrocarbon X contains 83.63% C and 16.37% H. a) Determine its empirical formula. b) Determine its molecular formula if MW = 86. c) Name X. d) How many liters of oxygen gas (d = 1.30 g/L) are required for the full combustion of 1.00 g of X? a) Assume 100.00 g of the hydrocarbon: 83.63 g C and 16.37 g H. Moles C = 83.63 g ÷ 12.01 g/mol = 6.963 mol C. Moles H = 16.37 g ÷ 1.008 g/mol = 16.24 mol H. Ratio C:H = 6.963 : 16.24 = 1 : 2.332 = 3:6.997 = 3:7. Empirical formula is C 3 H 7 . b) Empirical mass = 3×12 + 7×1 = 43. Empirical units in a molecule = 86/43 = 2. 6 H 14 . c) This formula conforms with the general formula C n H 2n+2 (where n = 6). Therefore X is an alkane – hexane. d) Combustion reaction: 2C 6 H 14 + 19O 2 12CO 2 + 14H 2 O, liters of O 2 required = 1.00 g hexane × (1 mol hexane / 86 g hexane) × (19 mol O 2 / 2 mol hexane) × (32.0 g O 2 / 1 mol O 2 ) × (1 L O 2 gas / 1.30 g O 2 ) = 2.72 L O 2 gas. 2 . Natural gallium has an average atomic mass of 69.72 amu and is composed of isotopes 69 Ga (M = 68.93 amu) and 71 Ga. The ratio of atoms 69 Ga/ 71 Ga in gallium is 1.5253.
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This note was uploaded on 06/13/2008 for the course CHEM 1 taught by Professor Kryatov during the Spring '08 term at Tufts.

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RecitationSet2_AnsKey - Tufts University - Chem 1 - Summer...

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