RDGcrystallization - Crystallization Revised 5/05/06...

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Crystallization Revised 5/05/06 1 CRYSTALLIZATION Crystallization is a common technique used to purify solids. Two common methods of crystallization are “gradual cooling” and “diffusion”. Gradual Cooling Gradual cooling involves dissolving the impure solid in a minimum amount of a hot solvent and allowing the resulting solution to cool slowly to room temperature. During the cooling process, pure (or almost pure) crystals form and are then collected by vacuum filtration. The first step in the crystallization process is to find an "ideal” solvent by testing a small amount of the impure solid. The desired compound should be very soluble in the solvent when it is hot (near the boiling), but only slightly soluble at room temperature. Sometimes a solvent mixture (two or more solvents in a specific ratio) is required to achieve this temperature dependent solubility. At the same time, the dissolved impurities (byproducts and unreacted starting material) should be highly soluble in the solvent at BOTH high and low solvent temperatures. The compound must precipitate out of solution at cooler temperatures to allow its separation from the solvent and the dissolved impurities by filtration. The next step is to dissolve the solid to be purified in a minimum amount of hot solvent.
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This note was uploaded on 11/23/2010 for the course CHEMISTRY Chem 1LC taught by Professor Dr.kimberlyedwards during the Fall '10 term at UC Irvine.

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RDGcrystallization - Crystallization Revised 5/05/06...

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