Recrystallization Part 1 (Laboratory Manual)
The essence of a re-crystallization is a purification. Messy, dirty, compounds are cleaned up, purified, and can then hold their heads up in public again. The sequence of events you use will depend a lot on how messy your crude product is, and just how soluble it will be in various solvents. In any case, you’ll have to remember a few things.
1. Find a solvent that will dissolve the solid while hot.
2. The same solvent should not dissolve it while cold.
3. The cold solvent must keep impurities dissolved in it forever or longer.
This is the major problem. And it requires some experimentation. That’s right! Once again, art over science. Usually, you’ll know what you should have prepared, so the task is easier. It requires a trip to your notebook, and possible, a handbook (see Chapter 2, "Keeping a Notebook" and Chapter 3, "Interpreting a Handbook"). You have the data on the solubility of the compound in your notebook. What’s that you say? You don’t have the data in your notebook? Congratulations, you get the highest F in the course.
Information in the notebook (which came from a handbook) for your compound might say, for alcohol (meaning ethyl alcohol), s.h. Since this means soluble in hot alcohol, it implies insoluble in cold alcohol (and you wondered what the i meant). Then alcohol is probably a good solvent for recrystallization of that compound. Also, check on the color or crystalline form. This is important since
1. A color in a supposedly white product is an impurity.
2. A color in a colored product is not an impurity.
3. The wrong color in a product is an impurity.
You can usually assume impurities are present in small amounts. Then you don’t have to guess what possible impurities might be present or what they might be soluble or insoluble in. If your sample is really dirty, the assumption can be fatal. This doesn’t usually happen in an undergraduate lab, but you should be aware of it.
Folding Funnels Paper - Bookshelf
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