Crystallisation
A purification technique in which a solid is separated from solution as an ordered crystalline lattice.
Unit
Dimensionless
In depth
A hot saturated solution is cooled slowly so that solubility falls and the desired compound deposits, while impurities present in smaller amounts remain dissolved in the mother liquor. Slow cooling gives larger, purer crystals because the growing lattice can reject foreign particles. Repeated recrystallisation raises purity further.
Examples in the real world
Purifying benzoic acid from hot water, and harvesting copper sulfate pentahydrate as deep blue crystals.