The recrystallization process separates impurities from a solid. Some impurities can cause, for example, a solid to have a different color to its pure form, or be weaker than it otherwise should.

This is achieved by dissolving the solid in a hot solvent and then cool that that solvent to allow the formation of crystals.

In order to perform the recrystallization of a compound, there are several steps that need to be followed.

Choose your solvent

The first step is choosing a solvent that is adequate for the solid to purify. The solvent must dissolve the solid when it's hot, but NOT when it's cold.

Dissolve your solid in the hot solvent

Heat up your solvent to its boiling point and dissolve the solid in it. Note that some of the impurities in the solid might not be soluble in the solvent.

Add activated charcoal and filter it

This step depends on the type of impurities in your solid. Once the solid is dissolved in your solvent, add a bit of activated charcoal. The activated charcoal will adsorb a lot of the impurities. After the activated charcoal has adsorbed the impurities, filter it out of the solution while it is still VERY HOT, otherwise, you might risk getting crystals in your funnel and filter. Remember to always use a filter the same size as the funnel for effective filtration.

Cool down the solution

The solution needs to be cooled down in two steps. First, the conical flask needs to be cooled down to room temperature, and once it is at room temperature, it can be placed in an ice bath for further cooling. If the solution is placed straight into an ice bath, the fast cooling and formation of crystals could trap some of the impurities again in the crystals, making the purification less efficient.

Enjoy your crystals!

If you performed these steps correctly you will see crystals starting to form in your flask. Those crystals will have fewer impurities than the original ones you dissolved.

Recrystallization Workflow