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Fractionalcrystallisation is the method used for separating two compounds with differentsolubilities in a solvent S. The process of fractional crystallisation iscarried out in four steps.
(a) Preparation of the solution: The powdered mixture is taken in a flask and the solvent isadded to it slowly and stirred simultaneously. The solvent is added till thesolute is just dissolved in the solvent. This saturated solution is thenheated.
(b) Filtration of the solution: The hot saturated solution is then filtered through a filterpaper in a China dish.
(c) Fractional crystallisation: The solution in the China dish is now allowed to cool. The lesssoluble compound crystallises first, while the more soluble compound remains inthe solution. After separating these crystals from the mother liquor, thelatter is concentrated once again. The hot solution is allowed to cool andconsequently, the crystals of the more soluble compound are obtained.
(d) Isolation and drying: Thesecrystals are separated from the mother liquor by filtration. Finally, the crystalsare dried.