Colegio de San Juan de Letran
College of Liberal Arts and Sciences
SEPARATION AND PURIFICATION OF ORGANIC COMPOUNDS: CRYSTALLIZATION
Gomez, Paola Anne M.
DOP: 2 July 2013
Student no. : 4120403
DOS: 9 July 2013
Engr. C. D. Sanchez
Crystallization is a technique which chemists use to purify solid compounds. It is one of the fundamental procedures each chemist must master to become proficient in the laboratory. Crystallization is based on the principles of solubility: compounds (solutes) tend to be more soluble in hot liquids (solvents) than they are in cold liquids. If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration. (orgchem.colorado.edu)
A desirable solvent for crystallization has the following properties: 1) dissolves the solute readily at an elevated temperature, but only sparingly at a lower temperature (room temperature); 2) gives no chemical reaction with the solute; and 3) is sufficiently volatile so that it may be removed easily from the purified crystals.
The crystallization process consists of two major events, nucleation and crystal growth. Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale (elevating solute concentration in a small region), that become stable under the current operating conditions. These stable clusters constitute the nuclei. However, when the clusters are not stable, they redissolve. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by the operating conditions (temperature,...
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