Crystallization
Crystallization is a technique which chemists use to purify solid compounds. It is one of the fundamental procedures each chemist must master to become proficient in the laboratory. Crystallization is based on the principles of solubility: compounds (solutes) tend to be more soluble in hot liquids (solvents) than they are in cold liquids. If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration.
This simplified scientific description of crystallization does not give a realistic picture of how the process is accomplished in the laboratory. Rather, successful crystallization relies on a blend of science and art; its success depends more on experimentation, observation, imagination, and skill than on mathematical and physical predictions. Understanding the process of crystallization in itself will not make a student a master crystallizer; this understanding must be combined with laboratory practice to gain proficiency in this technique.