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Molar Mass by Freezing Point Depression—AP* Chemistry Classic Laboratory Kit

By: The Flinn Staff

Item #: AP6356

Price: $30.20

With the Molar Mass by Freezing Point Depression Classic Lab Kit for AP* Chemistry, students calculate the freezing depression constant for BHT by measuring known freezing point values and calculating the molar mass of an unknown.

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Classic AP Requirement #4—Determination of Molar Mass by Freezing Point Depression

Students determine the molar mass of an unknown substance by measuring the freezing point depression of a solution of the unknown substance and the compound BHT (2,6-Di-tert-butyl-4-methylphenol). The freezing point of BHT is first determined, followed by the freezing point of a solution of the known substance dissolved in BHT. The freezing depression constant, kfp, for BHT is calculated from these values and used, along with the freezing point depression of a solution of the unknown substance and BHT, to calculate the molar mass of the unknown. Students gain the recommended familiarity with the observation and recording of phase changes. An alternative microscale procedure is included as a supplement.

Complete for 24 students working in pairs.

Molar Mass by Freezing Point Depression Inquiry Guidance & AP* Chemistry Curriculum Alignment Transition Guide available! Adapt this classic AP Chemistry experiment for guided-inquiry and correlate with the AP Chemistry curriculum framework with the Flinn Scientific Inquiry Guidance and AP* Chemistry Curriculum Alignment Guide. Follow the link in Resources to find this valuable publication!


Materials Included in Kit (for 24 students working in pairs): BHT, cetyl alcohol, stearic acid.
Additional Materials Required (for each lab group): For macroscale procedure: 0.001-g precision balance (shared), beaker, hot plates or Bunsen burners, ring clamp, rubber stopper with one hole, support stands, 18 x 150 mm test tube, thermometers (preferably graduated to 0.1 °C), universal clamp, weighing paper, wire gauzes, wire stirrers.
For microscale procedure: 0.001-g precision balance (shared), beakers, Thiele melting point tubes (optional), Bunsen burners or hot plates, capillary tubes, mortar and pestle or watch glass and test tubes, ring clamps, small rubber bands, rubber stoppers, stirring rods, support stands, thermometers with 0.1 °C divisions, universal clamps, wire gauzes.

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