Homework 1 Key

Homework 1 Key - CHEMISTRY 201X: Homework #1 (KEY)...

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Unformatted text preview: CHEMISTRY 201X: Homework #1 (KEY) "Isotopes and Mass Spectrometry" (1) (16 Pts) (a) (8 pts) Atomic Isotopes: Isotope 12 13 1 Due: Thursday, August 30, 2007 Mass (amu) 12.000000 13.003355 1.007825 2.014102 34.968853 36.965903 Abundance (%) 98.93 = uC 1.07 = vC 99.9885 = uH 0.0115 = vH 75.76 = uCl 24.24 = vCl C C H H Cl Cl 2 35 37 The various molecular isotopes of CHCl3 arise from all possible combinations = 2 2 4 = 16 different isotopes of chloroform. The relative abundances of each isotope can be worked out from 1 = (uC + vC)1(uH + vH)1(uCl + vCl)3 = uCuHuCl3 + + vCvHvCl3 Isotope 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 12 12 12 12 12 12 12 12 13 13 13 13 13 13 13 13 (16 terms) Abundance (> 0.01%) 43.01 41.29 13.21 1.41 0.00 0.00 0.00 0.00 0.47 0.45 0.14 0.02 0.00 0.00 0.00 0.00 Mass (amu) 117.914383 37 Mass (> 0.1 amu) 117.9 119.9 121.9 123.9 118.9 120.9 122.9 124.9 118.9 120.9 122.9 124.9 119.9 121.9 123.9 125.9 Abundance (%) 43.01282 41.28686 13.21005 1.408886 0.004947 0.004749 0.001519 0.000162 0.465215 0.446547 0.142876 0.015238 0.0000535 0.0000514 0.0000164 0.00000175 C H Cl3 C H Cl2 Cl C1H35Cl37Cl2 C H Cl3 C H Cl3 C H Cl2 Cl C H Cl Cl2 C2H37Cl3 C H Cl3 C H Cl2 Cl C1H35Cl37Cl2 C H Cl3 C H Cl3 C H Cl2 Cl C H Cl Cl2 C2H37Cl3 2 35 37 2 35 37 2 35 1 37 1 35 37 1 35 2 35 37 2 35 37 2 35 1 37 1 35 1 35 119.911433 121.908483 123.905533 118.920660 120.917710 122.914760 124.911810 118.917738 120.914788 122.911838 124.908888 119.924015 121.921065 123.918114 125.915164 (b) (4 pts) In this spectrum, those isotopes that have equal values in the column, Mass (> 0.1 amu), will lie on top of each other and add their intensities. CHEMISTRY 201X: Homework #1 (KEY) Isotope 1 5 9 2 13 6 10 3 14 7 11 4 15 8 12 16 12 12 13 12 13 12 13 12 13 12 13 12 13 12 13 13 Due: Thursday, August 30, 2007 Abundance (%) 43.01282 0.004947 0.465215 41.28686 0.0000535 0.004749 0.446547 13.21005 0.0000514 0.001519 0.142876 1.408886 0.0000164 0.000162 0.015238 0.00000175 0.00000175 0.015400 1.408902 0.144395 13.21010 0.451296 41.28691 Abundance (%) 43.01282 0.470162 Mass (> 0.1 amu) 117.9 118.9 118.9 37 C H Cl3 C H Cl3 C H Cl3 C H Cl2 Cl C2H35Cl3 C H Cl2 Cl C H Cl2 Cl C1H35Cl37Cl2 C H Cl2 Cl C H Cl Cl2 C H Cl Cl2 C H Cl3 C2H35Cl37Cl2 C H Cl3 C H Cl3 C2H37Cl3 1 37 2 37 1 37 1 35 37 2 35 37 2 35 37 1 35 37 2 35 37 1 35 1 35 2 35 1 35 119.9 119.9 120.9 120.9 121.9 121.9 122.9 122.9 123.9 123.9 124.9 124.9 125.9 50 Relative Abundance (%) 40 30 20 10 0 117.9 118.9 119.9 120.9 121.9 122.9 123.9 124.9 125.9 (amu) (c) (4 pts) In this spectrum, only those isotopes whose abundance exceeds 0.01% will be observed. This is limited to isotopes (1)-(4) and (9)-(12) above. CHEMISTRY 201X: Homework #1 (KEY) Due: Thursday, August 30, 2007 50 Relative Abundance (%) 40 30 20 10 0 117.9 118.9 119.9 120.9 121.9 122.9 123.9 124.9 (amu) In principle, there would be one less peak than in (b) above, but the relative abundance of the heaviest isotope is quite small and on this scale, is not seen. (2) (20 Pts) (a) (4 pts) V m = M M + m - 1 VM (b) (4 pts) VM + m VC3H8 = = 1.001655 ; VM VCO2 12 16 M + m = Mass of 12C31H8 = 44.062600 amu -1 V M = Mass of C O2 = ( M + m ) M + m = (44.0626 amu)(1.001655)-1 VM = 43.989797 amu Atomic mass of 16O = (43.989797 amu - 12.000000 amu) / 2 = 15.994899 amu (c) (4 pts) Mass (12C21H4) = 28.031300 amu Mass (12C16O) = 27.994899 amu m = Mass (12C21H4) - Mass (12C16O) = 0.036401 amu (d) (4 pts) m(1) = Mass (14N2) - Mass (12C16O) = 0.01128: Mass (14N) = 14.00309 amu CHEMISTRY 201X: Homework #1 (KEY) Due: Thursday, August 30, 2007 m(2) = Mass (12C31H8) - Mass (14N216O) = 0.06176: Mass (14N) = 14.00297 amu Since the two measurements give different results, we must take the average value: Mass (14N) = 14.00303(6) amu. (Better results are obtained with more data to average.) (e) (4 pts) Mass (12C21H6) = 30.04695 amu Mass (14N16O) = 29.99793 amu m = Mass (12C21H6) - Mass (14N16O) = 0.04902 amu ...
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This homework help was uploaded on 03/27/2008 for the course CHEM 201 taught by Professor Miller during the Fall '07 term at Iowa State.

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