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hmwk3additional - abundances of the various oxygen isotopes...

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Chemistry 2090 Stable Isotopes? Your name here: September 12, 2008 In natural abundance, 98.9% of all C atoms are the isotope 12 C, and the remainder, 1.1%, are the isotope 13 C. Assume, contrary to fact, that these atoms are randomly distributed throughout all of the carbon-containing compounds on earth. 1. You are given a collection of molecules of carbon dioxide, CO 2 . What percent of them contain exactly 1 13 C atom? 2. The carbon dioxide is used to make a new molecule, a sugar, which is subsequently fermented to form ethanol with chemical formula C 2 H 6 O. What fraction of the ethanol molecules contain exactly 1 13 C atom, and what fraction contain 2 13 C atoms? 3. The heavy isotope of hydrogen, 2 H, appears with natural abundance 0.015%; that is, if you are given 100,000 hydrogen atoms, 15 of them will correspond to the heavy isotope; similarly, the
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Unformatted text preview: abundances of the various oxygen isotopes are: 16 O found in 99762 atoms out of 100000; 17 O in 38 out of 100000, and 18 O in 200 out of 100000. If you send a sample of ethanol into a mass spectrometer for weighing a small fraction of the molecules will appear with molecular weight 48 (ordinary ethanol having molecular weight 46) corresponding to the various combinations of 6 isotopic species: 13 C 2 1 H 6 16 O 13 C 12 C 1 H 5 2 H 16 O 13 C 12 C 1 H 6 17 O 12 C 2 1 H 4 2 H 2 16 O 12 C 2 1 H 5 2 H 17 O 12 C 2 1 H 6 18 O Rank order the likelihood that that molecule corresponded to mass 48 corresponds to each of these possibilities; place the most likely version at the left, the least likely at the right. You need not calculate the probabilities; only the relative likelihoods. 1...
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