Acetanilide: Purification Technique

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Name: Richard Perez Experiment Due Date: 9.18.14 Name of your section instructor: Min Fan Section: 239 Recrystallization Introduction The purpose of the experiment is to introduce students to the purification techniques: vacuum filtration and recrystallization, in addition to using the Mel-Temp apparatus for melting point analysis. The task in part A, is to take crude Acetanilide (composed of Acetanilide and two impurities: A & B), and isolate the Acetanilide using the purification techniques. After isolating the Acetanilide, find its melting point range. In part B of this experiment, the students are given a crude compound, composed of Naphthalene and an impurity, and they are to isolate and record the melting point of Naphthalene using…show more content…
Hot Vacuum filtration utilizes the fact that compounds may have different solubilities in different solvents at different temperatures. Solubility is how much of a solute will dissolve in a given solvent and temperature. In the case of part A, using H2O as the solvent, impurity A is much more soluble in H2O (~100℃) than Acetanilide, and impurity B is much less soluble than both in these conditions. On the molecular level, these solubilities relate to when there is enough energy in the system (~100℃) for the H2O molecules to bump into the compounds and bond to the partial charges all around of the molecules such that they become surrounded by H2O and separated from the other molecules. H2O is used because it is a polar molecule and we have polar compounds. Since in the given conditions, Acetanilide and impurity A will be dissolved, while impurity B…show more content…
The next step in the experiment was to reheat the solution in the filter flask to re-dissolve the crystals and then slowly cool the solution to permit recrystallization. Recrystallization was moderately successful because crystals were collected from the cold filtration step, but to determine if recrystallization was successful, an analysis of the melting points of the end products from part A and B had to be done. The melting point of pure Acetanilide is 114.3 ℃. The purified sample had a melting point range of 79.0℃ - 94.0℃. This melting point range is much lower than pure Acetanilide, but that may be due to H2O acting as an impurity. H2O is not a bad impurity to have, because it is easy to get rid of. Nevertheless, it may have lowered the final melting point range. For part B, recrystallization proved again moderately successful because crystals were formed, free of the pink color (signals that there may be a lot of impurity left). Pure Naphthalene has a melting point of 80.2℃. The purified sample from the experiment has a melting point range of 65.0℃-75.2℃. Once again, this is lower than the pure substance melting point but the sample was wet when it was placed in the Mel-temp apparatus and as stated before, H2O can act as an

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