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Chem 21

Fall 2009

Experiment 9 — Recrystallization
_____________________________________________________________________________ Pre-lab preparation. (1) Read the supplemental material from Zubrick, The Organic Chem Lab Survival Manual. (2) Draw the structure of acetanilide and report relevant physical data. Be sure to cite the source of the data. You should be able to figure out what's relevant by reading the procedure. (3) Find and report the boiling points of the solvents you will be using for this experiment. (4) Outline the steps in the recrystallization of acetanilide.

Recrystallization involves dissolving a solid in a solvent and crystallizing it again, taking the opportunity to discard impurities along the way. One normally chooses a solvent in which the solubility increases significantly with temperature. The solid is dissolved in a minimal amount of hot solvent, and the solution is filtered to remove insoluble impurities. Upon cooling the solution, the desired compound crystallizes, leaving soluble impurities in solution. Alternatively, a mixed solvent system can be used to modify the solubility — the key is to get the compound into solution then get it back out of solution. Ideally, one would like to recover all of the desired solid completely free of contaminants. Unfortunately, this is rarely possible. Usually, if most of the material is recovered, it is not very pure, and extremely pure material can be obtained only in low yield. The trick is to find the proper balance between yield and purity. Now to the specifics of the problem at hand. Over the summer, certain stockroom personnel had an unauthorized juggling contest and accidentally dumped all the acetanilide on the floor. Unfortunately, the floor wasn't very clean, now the material is contaminated with what appears to be rodent hair, gravel, dead spiders, etc. They were able to remove most of the dead roaches. Your mission, should you decide to accept it... well, you really have no...
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