Question

What is the basis of fractional crystallization?

Answer 1

1. Definition: The process of separating two or more crystalline solids based on the difference in their solubilities in the same solvent is called fractional crystallization.
2. This method is feasible only if the solubility of two crystalline solids, in a particular solvent differs widely.
3. A mixture of crystalline solids is dissolved in a common solvent at a higher temperature than room temperature.
4. Upon cooling this mixture to room temperature, the less soluble constituent begins to crystallize first, followed by the more soluble constituent.
5. By repeating this process in a minimum amount of hot solvent, the two solids can ultimately be separated.
6. For example, Sodium chloride $\left(\mathrm{NaCl}\right)$ being less soluble crystallizes out first from a saturated solution of a mixture of Potassium nitrate $\left({\mathrm{KNO}}_3\right)$ and Sodium chloride