Advantages And Disadvantages Of Recrystallization

Recrystallization is a common technique used for purifying an impure compound within a solvent. This method of purification is based on the principle that the solubility of most solids increases with higher temperature. For this type of purification, an impure compound is first dissolved to prepare a highly concentrated solution at a high temperature. Following this the solution is cooled, which drops the temperature and causes the solubility of the impurities in the solution, along with the substance being purified, to decrease. The impure substance then crystallizes before the impurities, leaving them behind in the solution. The slower the cooling, the bigger the crystals that will be formed. Finally, a filtration process must be used to isolated the purer crystals from the less pure ones. Solubility curves can also be used in order to predict the outcome of a recrystallization procedure.1

Furthermore, it can only be done correctly if the proper solvent is used. This solvent can be obtained by trial and error based on predictions and observations, but the solution needs to be soluble at high temperatures and insoluble at low temperatures.1 One way to determine a correct solvent for recrystallization is to look at the structural features of both the solute and solvent. This is due to the fact that compounds which share similar structural features are more likely to be soluble in one another. Some features that affect solubility include polarity and the ability to hydrogen bond.2 When carried out correctly, recrystallization is a very effective technique to obtain a pure sample of a