Question

Explain and evaluate the effectiveness of the recrystallization solvent in terms of percent recovery and purity of the recrystallized solid

Answer 1

Recrystallization is the process of purification of a compound by crystallizing it again by dissolving it in a particular recrystallization solvent.

The effectiveness of the recryatallization solvent can be evaluated in terms of percent recovery and purity of the recrystallized solid on the basis of the following two parameters:

If the recrystallization solvent volume is too low:

If the volume is too low, then the percentage purity of the sample will decrease. Because of the absence of enough amount of solvent volume crystallization process is fast, solvent evaporates quickly to give small sized crystallized compound and thus a fraction of both impure and pure solid are obtained thereby decreasing the overall percentage recovery of the pure compound.

If the recrystalliztion solvent volume is too high:

But if the solvent volume is too high, then the crystallization process becomes time consuming but a better yield and good recovery of the solid sample is observed in this case because the nucleation (accumulation of pure compound to give the desired crystals) is slow as a result highly pure compounds are obtained with almost 100% percent recovery.