chm 2045 quiz 1 key

chm 2045 quiz 1 key - CHM 2045 Quiz #1 September 11, 2007...

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CHM 2045 Quiz #1 September 11, 2007 Name: TA solution Section: Show all your work!!! The quiz is worth 20 points. Question # 1 The scientists at UF were analyzing soil samples from a volcano site and found a new element, element Xy. They found that element Xy has an average molecular weight of 120.03g/mol. Element Xy exists as two isotopes, 119 Xy with a molecular weight of 118.998751u, and 121 Xy with a molecular weight of 120.912345u. Calculate the percentage of abundance for each isotope. (5 points) ) 1 ( 992345 . 120 998751 . 118 03 . 120 x u ux u + = ux u ux u 992345 . 120 992345 . 120 998751 . 118 03 . 120 + = ux u 993594 . 1 962345 . 0 = 48 . 0 993594 . 1 962345 . 0 = = x % abundance 119 Xy = 48% % abundance 121 Xy = 52% Question # 2 A pure compound contains 72.066 g of carbon, 12.095 g of hydrogen, and 95.996 g of oxygen and has a molar mass of 180.157 g/mol. What is the empirical AND molecular formula of this compound? (5 points) molC molC g gC 0055 . 6 / 12 066 . 72 = 1 9998 . 5 0055 . 6 = Empirical Formula: CH 2 O molH molH g gH 095 . 12 / 008 . 1 095 . 12 = 2 9998 . 5 095 . 12 = MW CH 2 O = 30g/mol molO molO g gO 9998 . 5 / 00 . 16 996 . 95 = 1 9998 . 5 9998 . 5 = Real MW = 180.157g/mol 6 30 180 = So, the molecular formula is C 6 H 12 O 6 Question # 3

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This note was uploaded on 04/24/2008 for the course CHM 2045 taught by Professor Mitchell during the Fall '07 term at University of Florida.

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chm 2045 quiz 1 key - CHM 2045 Quiz #1 September 11, 2007...

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