SolutionsExtraction, Crystallization and Sublimation
1. Choose the technique
Which technique would you use to: a) purify impure benzoic acid, very soluble in hot water and only slightly soluble in cold water; b) separate iodine from sodium chloride; c) separate an amine from a neutral compound, both dissolved in ether?
- Crystallization from water by cooling.
- Sublimation: iodine sublimes and NaCl does not.
- Acid-base extraction with aqueous HCl: the amine passes into the water as an ammonium salt.
2. The property exploited
Which physical property is each of the three techniques based on?
- Extraction: the different solubility of the compound in two immiscible solvents.
- Crystallization: the change of solubility with temperature or solvent.
- Sublimation: the high vapour pressure of the solid, which turns into gas without melting.