Chem 3AL - Lab Report #6 - Kylie 19 July 2010 Chem 3A Lab...

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Kylie 19 July 2010 Chem 3A Lab Experiment #7 Discussion: After making full-size sketches of all TLC plates, we compared them to see the relative Rf values and overall positions of the known compounds. We decided not to use 60:40 hexane:ethyl acetate because acetaminophen and ibuprofen barely moved from the starting line, making it difficult to get their accurate Rf values for identification as well as distinguish them from each other. We also decided not to use 100% ethyl acetate for similar reasons; caffeine barely moved from the starting line, and the aspirin and ibuprofen spots lay nearly on the same horizontal line. 92:8 ethyl acetate:acetic acid and 10:10:1 toluene:ethyl acetate:acetic acid were the suitable TLC solvents because the known components were evenly spread out, and all of them had moved at least ~1cm away from the starting line. This resulted in Rf values that were distinct and not too close to each other, which would make matching and identifying easier in Part II. After developing TLC plates (using the 2 chosen solvent systems) of the compound groups listed in Table E7.1, we compared the resulting sketches and Rf values. We looked for known compounds that lined up with the unknown, and noticed that in both the 10:10:1 and 92:8 solvent systems the aspirin spot was right next to the unknown one. As a result, aspirin #1, unknown #1, aspirin #2, and unknown #2 all had very close Rf values (~0.62, with 0.7 being an outlier because I may have developed unequal amounts and measured the spot incorrectly). Acetaminophen's Rf values were too far off from the unknown's, and its spots were dark with iodine stains; because of all these differences, Tylenol and Excedrin were cancelled out. In the other two TLC plate groups, the unknown ended up between caffeine and ibuprofen with
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significant distance from both, showing that their Rf values would not match up. And though
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This note was uploaded on 06/27/2011 for the course CHEM 3AL taught by Professor Li during the Summer '08 term at University of California, Berkeley.

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Chem 3AL - Lab Report #6 - Kylie 19 July 2010 Chem 3A Lab...

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