Solvent pair recrystallization is a process in which a solute is dissolved in two different solvents and the crystals are separated. The crystals of the original solvent pair can be used to determine the identity of the unknown solute.
Recrystallization is an important technique for purifying substances from mixtures. It can be used when you need to separate two compounds that are very similar or even identical in structure, but have different physical properties such as melting point or boiling point.
For example, imagine that you have a mixture of two substances, A and B. Suppose that A has a higher melting point than B. You could dissolve them both together in a solvent that does not mix with either compound completely and heat until all of A has dissolved but most of B remains undissolved (because it has a lower melting point).
The resulting solution would consist mostly of A with some B mixed in and would contain no impurities except those present initially in A or B themselves (because they were mixed before heating). If you cooled this solution down, solid A would precipitate at first as crystals grow out of solution because its solid form melts at a higher temperature than its liquid form.
Last modified: October 8, 2022