i
Search icon

Organic Chemistry

Self Learning   /   Study Material   /   Crystallization
Previous
Next

Crystallization

Crystallization: Crystallization is the process of purification of stable organic compounds based on the differences in the solubility of compounds and the impurities in a suitable solvent. The impure compound is dissolved in a solution in which it is soluble at room temperature but appreciably soluble at the higher temperature. Pure compounds crystallize out and are separated by filtration. Impurities imparting colour to the solution are removed by adsorbing over activated charcoal.

Different types of Crystallization

  1. Simple Crystallization: A crystallization technique which  involves the preparation of the saturated solution of the impure organic compound in a solvent at a higher temperature  near its boiling point.

The solution formed is filtered when it is hot in order to remove insoluble impurities. The clear solution thus obtained is cooled when the solid organic compound separates in the form of crystal.

Example of simple Crystallization:

Separation of sugar from a mixture of sugar and common salt by using ethanol, separation of the mixture of naphthalene and phthalic acid by hot water, separation of the mixture of benzoic acid and naphthalene etc.

  1. Fractional Crystallization: It involves the separation of a mixture of two compounds which are soluble in the same solvent, but their solubility is different. The not saturated solution of the mixture is allowed to cool. The less soluble component crystallizes out earlier than, the more soluble components. Process of separating the components of a mixture by repeated and successive Crystallization is called fractional or selective Crystallization.

Example:

Glucose and fructose are soluble in water as well as in alcohol, glucose being less soluble than fructose in both of these solvents and thus crystallizes first.

KClO3 is less soluble than KCl and are separated by this method.

© All rights Reserved | SelfLearning.io