# class2 - Class#2 Representations Composition of Molecules...

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Class #2 Representations & Composition of Molecules CHEM 107 A. Bengali Texas A&M University Qatar

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) Numbers of molecules are huge ) Use moles as a unit of quantity ) 1 mole = 6.022 x 10 23 (“Avogadro’s Number”) ) This is an experimentally measured number
Avogadro’s Number ) Defined by setting 1 mole 12 C = 12 g ) Definition of the amu is 1 atom 12 C = 12 amu ) Mass of an atom or molecule in amu is numerically equal to mass of one mole in grams

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mass, moles, # of molecules, . .. ) Converting between these is just changing units. ) Use atomic & molecular weights, densities, etc. as needed.
Simple Mole Calculation ) An aluminum bicycle frame weighs about 2.7 pounds. ) How many moles of aluminum is that?

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Mole Problem 2.7 lbs Al = ? Moles Al ) What do we know? atomic wt. of Al = 27, so: 27 g Al = 1mol of Al ± Now just convert units! lbs g moles
Mole Problem 2.7 lbs Al = ? Moles Al 1 mole Al = 27 g Al 1 pound = 454 g 2 .7 lbs Al x 454 g 1 l b x 1mole Al 27 g = 45.4 mol Al

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Representing Molecules ) Names : ethanol, ethyl alcohol ) formulas C 2 H 6 O, C 2 H 5 OH, CH 3 CH 2 OH ) structural drawings ) models
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class2 - Class#2 Representations Composition of Molecules...

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