Fractional Crystallization

The technique of fractional crystallization is used by chemists to separate a mixture of dissolved substances (salts) in a solvent into its purified components (salts).
This is accomplished by taking advantage of the variation of solubility of different salts in a given solvent with temperature. The solution containing the mixture is evaporated until the least soluble substance (salt) crystallizes out.

In this experiment you will be given a sample containing potassium dichromate K2Cr2O7 and sodium chloride NaCl, both of which are water soluble ionic substances, with different solubilities at different temperatures. Sodium Chloride exhibits little change in solubility between the range of 0 °C to 100 °C, while potassium dichromate solubility increases 16-fold over the same temperature range. This property can be used to separate a mixture of the two salts from a solution.