cryst2 - Chem 267 Recrystallization Part 2(revised 7/10...

Chem 267 . Recrystallization - Part 2 . (revised 7/10).
Recrystallize benzoin if you did not do it the previous week. You will also recrystallize an unknown.
Review the techniques such as vacuum (or suction) filtration and filtration using the pipet method.
Lab Clean-up . For reasons of safety and effectiveness, an essential part of lab work is keeping the lab
in a clean and orderly state. Please keep bottles capped. Many chemicals will lose their effectiveness
or evaporate if left open to the atmosphere. If caps are not in place, the potential also exists for toxic
chemicals to enter the lab atmosphere. Please clean up spills immediately so others do not become
contaminated. Most of you will soon join a research group. You will quickly find that sloppy and
unsafe behavior is not tolerated one bit by your advisor or coworkers. Learning good lab habits now
will help greatly later on.
Waste Disposal : place all liquid wastes from these experiments into the Nonhalogenated Liquid
Waste container. In your prelab outlines remember to always include procedures for the proper
disposal of wastes as described in the handout for that experiment.
(1.) Purification of an Unknown . Using two different solvents you will recrystallize two 60 mg
samples of an unknown that is contaminated with soluble impurities. Your TA will assign the
unknown to you. You must first determine suitable recrystallization solvents by doing solubility tests
and preparing a table as before. Several solvents are available to you in this experiment. These are
water, methanol, ethanol, ligroin, and toluene. Try as many of these solvents as necessary to find at
least two that work well. The ideal solvent is one that produces the highest recovery of the purest most
well-formed crystals. One of the two that you choose will probably work better in terms of
purification or yield.