Question

Describe the method which can be used to separate two compounds with different solubilities in a solvent S.

Answer 1

Fractional crystallization is used to separate two compounds with different solubilities in a solvent. The process of fractional crystallization is carried out in 4 steps:

• Preparation of the solution: The powdered mixture is taken in a flask and the solvent is added to it slowly and stirred simultaneously. The solvent is added till a saturated solution is obtained and then it is heated.
• Filtration of the solution: The hot saturated solution is then filtered through filter paper in a china dish.
• Fractional crystallization: The solution in the china dish is now cooled. The less soluble compound crystallizes first, while the more soluble compound remains in the solution. After separating these crystals from the mother liquor, the latter is concentrated once again. The hot solution is allowed to cool and consequently, crystals of more soluble compounds are obtained.
• Isolation and drying: These crystals are separated from the mother liquor by filtration. Finally, the crystals are dried.