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A good solvent for recrystallization depends entirely on the polarity of the solid you're trying to purify. For example sodium chloride readily dissolves in water whereas naphthalene dissolves only in nonpolar solvents like hexane. To select a good solvent first consider the polarity of the compound of interest and pick a solvent that has the potential to dissolve it. Next suspend the solid in that solvent. You must pick another solvent if the solid completely dissolves in the selected solvent. Heat the mixture while stirring. If you reach the boiling point of the solvent and the compound hasn't dissolved, you must find a different solvent or add more of the solvent you are currently using. If your solid completely dissolves without too much of the chosen solvent, you have yourself a good solvent for recrystallization. To continue with the recrystallization simply allow the solvent to cool and your solid should precipitate out in the form of crystals. Put it in an ice bath to assist with the precipitation. The latter technique can lead to small crystals or powder. The best way to remedy this is to do a slow recrystallization. To do this you must use two solvents that will evaporate over a long period of time. One solvent must be very volatile and must be able to easily dissolve your compound at room temp. The other must be less volatile and your compound must be insoluble in this solvent. Note that this solvent must have the potential for dissolving the impurities in your compound. To perform the recrystallization, dissolve your compound in the "good" solvent and then add about the same amount of the "bad" solvent. Over a period of time, the "good" solvent should evaporate leaving your crystallized product in the "bad" solvent without any impurities.
