Stage1. Dissolve sample in a minimum value of hot water.Why does it have to be minimum value and hot water?Please Help. THANK YOUPurfying acid by recrystalisation.

2 Answers | Add Yours

mlsiasebs's profile pic

mlsiasebs | College Teacher | (Level 1) Associate Educator

Posted on

Recrystallizations require that we dissolve the sample in a solvent (usually hot).  We heat the solvent to maximize the solubilty of our compound and then allow it to cool which lowers the solubility of the compound.  As a result, the crystals will form as the solution cools.  The impurities are (hopefully) in very small amounts so they will remain soluble in the solvent even when it cools.  If the compound has some solubility in the cooled solvent, we may lose a small amount of our compound but the amount that we obtain will be more pure than without recrystallization.  If we have excess solvent, cooling the sample will not result in the recrystallization because it can remain dissolved in the solvent. 

Choice of the solvent for recrystallization is important because we have to know something about the identity and solubility of our potential impurities as well as our desired compound.



We’ve answered 317,706 questions. We can answer yours, too.

Ask a question