Question #e7b58
1 Answer
Aug 27, 2014
The only way to make an unsaturated solution produce crystals is first to make it saturated.
There are two possible ways to do this.
- Allow the solvent to evaporate.
As the solvent evaporates, the solution becomes more concentrated. Once it becomes saturated, the evaporation of any more solvent would make the solution supersaturated. So crystals of solute will precipitate from the solution.
- Cool the solution.
This will not always work. Solubility decreases as the temperature decreases. If the solvent doesn't freeze before the solution becomes saturated, then cooling the solution will cause crystals of solute to form.
Often, an impure substance is purified by preparing a hot, almost saturated, solution and allowing it to cool.
