The Modern Chemistry Lab

Purification Is Essential

How does crystallization purify compounds?

Crystallization as a purification technique relies on the fact that it is usually much easier to form a crystal from a single chemical species than it is to form a crystal from a mixture of chemical compounds. Recrystallization is the process of dissolving a crude, impure product in a hot solvent (or mixture of solvents) and allowing it to crystallize out of the solution form as the solvent cools. Once a small crystal, even one so small we can’t see it, begins to form, it is relatively easy for other molecules of the same compound to add to the crystal. Other compounds will not be able to readily add to this crystal, which results in the formation of a crystal containing a single, pure chemical compound.


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