Recrystallization is a method to purify solid compounds based on the differences in solubility in a solvent.
1-Choosing the solvent or solvent pairs, 2-dissolving the sample in the minimum volume of the hot solvent, 3-cooling the saturated solution, 4-collecting and washing the crystals, and 5-drying.
An ideal solvent has the following characteristics: it completely dissolves the solute only at high temperatures (near the boiling point of the solvent); it does not react with the solute; it has approximately the same polarity as the solute; it precipitates the solute at low temperatures (near room temperature or lower); and it only dissolves impurities at low temperatures.
A solvent-pair is used when a single solvent with ideal properties cannot be found.
The two phases of crystallization are nucleation and crystal growth. During nucleation, solute molecules come together to form small stable crystals called nuclei. Then, additional crystal growth occurs on the nuclei, increasing the size of the crystals. This is because solute molecules have a higher affinity for joining existing solute crystals than forming new crystals.
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