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chem262lexp1 - liquid component is pulled through and...

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AtLee Watson Chem 262L Section 415 TA: Jeff Mighion Experiment 1: Purification of Unknown Using Recrystallization Upon recrystallizing the unknown crude sample of mass 0.501g, the purified product weighed 0.399 g and the percent recovery was calculated to be 79.6%. The recrystallized product appeared white and powdery. The determined melting point of the pure unknown was 234.5 0 C - 242.6 0 C. Possible melting points were examined, and the unknown was determined to be ρ-chlorobenzoic acid. The actual melting point of ρ-chlorobenzoic acid is 239 0 C - 241 0 C, thus one can deduce the unknown to be ρ-chlorobenzoic acid. In the experimental procedure, hot ethanol was used because the unknown would not have been soluble in cold ethanol. Without dissolution of the sample, filtration techniques would be futile because the impurities would remain in the sample. In recrystallization experiments, suction filtration would be chosen, not gravity filtration. In gravity filtration, one filters the sample and saves the liquid component, while in suction filtration (or vacuum filtration) the
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Unformatted text preview: liquid component is pulled through and discarded. The desired solid product is kept can then be washed, dried, and weighed to determine its purity. Hot filtration was performed because the impurities of the unknown sample are not soluble in the hot solvent. Thus, the hot filtration of the sample would separate the impurities from the sample. One possible problem with cooling the crystallization solution too quickly is the risk of collecting impurities in the newly formed crystals. These impurities would cause the melting point of the final purified product to be lower than the actual melting point because pure substances will boil at a higher range than samples with precipitates. The melting point of the purified sample coincided closely to the actual melting point of ρ-chlorobenzoic acid. This data implies that there were few impurities in the purified sample and that the solution was filtered and cooled accurately. Pledge:____________________________...
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