12.18.    Give a brief description of the principles of the following techniques taking an example in each case.

               (a)  Crystallisation

Answers (1)
M manish

Crystallisation-
It is one of the most commonly used techniques for the purification of solid organic compounds. Its principle is based on the difference in the solubilities of the compounds and the solvent's impurities. The impure compounds are dissolved in solvent but they are sparingly soluble at room temperature but soluble at the higher temperature. On cooling the compound, the pure compounds get crystallise and removed by filtration. 
For example- pure aspirin is obtained by recrystallising crude aspirin. Around 2 - 4 g of crude aspirin is dissolved in 20 mL of ethyl alcohol and the solution is heated for complete dissolution. Then after crystal formation, they can filter out and dried.
 

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