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chem233_postlab2 - are many nitrogens and carbonyl groups...

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1. The Rf values for unknown A are .29, .68, and .78. For unknown D they are .29, .60, and .68. 2. The standards that unknown A corresponds with are acetasalicylic acid, caffeine, and salicylamide. Unknown D corresponds with acetaminophen, acetasalicylic acid, and caffeine. 3. The analgesic drugs the unknowns correspond to are B.C. for unknown A and Excedrin for unknown D. 4. The relationship value between substance polarity and Rf value are that polar substances will not travel as far as nonpolar substances on a polar stationary phase, so the Rf value will be lower. In general, the more polar a substance the lower the Rf value. 5a. Substance number 5, salicylamide, is the least polar because it traveled farthest. An aromatic ring is present in the molecule, which contributes most to its nonpolar behavior. 5b. Substance number 3, caffeine, is the most polar because it traveled the least distance. There
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Unformatted text preview: are many nitrogens and carbonyl groups which contribute to its polar status. 6. If the stationary phase was changed to be nonpolar and the mobile phase was now polar, then the substances that were more polar would actually travel farthest in this situation. The distances would be opposite of what was seen in the experiment, similar to flipping the TLC plate over and then measuring distances. 7a. A nonpolar mobile phase should be used instead of the polar 1% acetic acid in ethyl acetate. This would make the unknown, which is most likely nonpolar based on its previous Rf value, travel a short distance, which would then be an Rf of .25. 7b. Petroleum ether is an example of a nonpolar mobile phase that would provide the desired Rf value....
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