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Topic: recrystalization  (Read 5288 times)

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« on: April 24, 2004, 09:39:15 PM »
Can someone tell me how to recrystalize out of hot methanol

Offline hmx9123

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« Reply #1 on: April 25, 2004, 01:34:58 AM »
Recrystallization is a process used extensively in order to purify a substance.  The basic idea is to take your substance, dissolve it in a minimum amount of hot solvent, then slowly cool the solvent to lower the solubility of the substance in your solvent.  As the solubility drops, the solution becomes saturated, then crystals begin to form because not enough solvent is present at the lower temperature to hold the compound.

In your case, you're using methanol.  So, take boiling (or hot) methanol, and add it slowly a little at a time to your sample, with stirring.  As soon as it's all dissolved, let the solution stand.  Don't move it, don't cool it faster with ice or anything yet.  The less the solution moves and the slower it cools, the larger the crystals you get.  Once your solution slowly cools to room temperature, you might have crystals starting to form.  If so, just let them form.  If not, then it's time to stick the solution in an icebath and let it stand for a while.

The ideal way to recrystallize is to find a solvent in which your sample is difficultly soluble, moreso at higher temperatures, and in which any impurities are much more soluble.  Then you recrystallize, which gives you purer crystals of your compound as the impurities stay in solution.  You lose some of your sample, as part of it is held up in the solution as well, but usually more of the impurities are left behind.

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