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Organic compounds (solids) can be purified by a method called crystallization.
Crystallization works by dissolving the material to be purified in a solvent (under hot conditions), followed by slow cooling of the solution. If the impurities are also soluble just like the substance we are purifying, obviously the purification will not be that effective. After the crystallization by slow cooling is completed, the crystals are collected by vacuum filtration. Then the crystals are dried.


Qualities of the Solvent Used for Crystallization

  1. The compound that is purified should be soluble in the selected solvent, only at high temperatures. At low temperatures, the compound should be insoluble.
  2. The solvent used should have a relatively low boiling point. The boiling point of the selected solvent should not be higher than the melting point of the compound to be purified.
Solubility depends on the polarities of the solute and the solvent. According to the principle “like dissolves like,” if the solute is polar, the solvent required should be polar too. On the other hand, if the solute is nonpolar, a nonpolar solvent should be used.
Some of the solvents commonly used for crystallization include acetone, chloroform, methanol, benzene, diethyl ether, carbon tetrachloride, and water.

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