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Chem 162 Lab 5

Fractional Crystallization and Temperature Dependence of Solubility

vacuum filtration of KNO3 crystalsThe objectives of this experiment are to use fractional crystallization to purify a sample of potassium nitrate containing a small amount of ferrous ammonium sulfate and to determine the solubility curve for potassium nitrate.


In part I of this experiment, crystallization and recrystallization are examined as a purification technique. This technique exploits the differences in solubility of the components in a mixture - the desired compound is crystallized while impurities remain in solution. Using fractional crystallization, a 10:1 mixture of KNO3 and (NH4)2Fe(SO4)2 6H2O will be purified, with the aim of recovering pure KNO3 crystals.


In the second part of this lab, the crystallization temperature (the temperature at which crystals begin to form) of six solutions of different KNO3 concentrations will be measured in order to determine the solubility curve for KNO3.

  • Prelab
    • Intro (pdf 163 KB, rev 10/21/12)
    • Required Prelab Assignment in Canvas (due Tuesday 8/6 at 11:30 am)
    • Review Materials & Procedure
    • Review Demonstration




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