Step 5 Crystallization
When a liquid (solvent) holds the maximum amount of a solid (solute) in solution at a given temperature, the solution is called a saturated solution. The fundamental rule of crystallization is that a solvent can generally hold more solid in solution at its boiling point than it can at room temperature. For example, if a given volume of solvent can hold 6 g of solid in solution at its (the liquid’s) boiling point and only 0.5 g of solid in solution at room temperature, then 6.0 – 0.5 = 5.5 g of solid can be recovered by crystallization from this volume of solvent. Thus, crystallization depends on the solubility of the solid at two temperatures, the boiling temperature and room temperature. The ideal solvent is one in which the solid is very soluble at the boiling temperature and very insoluble at room temperature