Molar Mass by Freezing Point Depression—Classic Laboratory Kit for AP® Chemistry
By: The Flinn Staff
Item #: AP6356
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
Determine the molar mass of an unknown by measuring the freezing point depression of its solution with 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 by measuring the freezing point for known solutions and is then used 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! Follow the link in Resources to find this valuable publication that lets you adapt this classic AP Chemistry experiment for guided-inquiry and correlate with the AP Chemistry curriculum framework.
Materials Included in Kit:
Cetyl alcohol, flake, 30 g
Stearic acid, reagent, powder, 30 g
2, 6-Tert-butyl-4-methylphenol, BHT, 200 g
Additional Materials Required (for each lab group): 0.001-g precision balance (shared), beaker, capillary tubes, hot plates or Bunsen burners, mortar and pestle, ring stand, ring clamp, rubber bands, rubber stopper with one hole, stirring rods, support stands, 18 x 150 mm test tubes, thermometers (preferably graduated to 0.1 °C), Thiele melting point tubes (optional), universal clamp, watch glass, weighing paper, wire gauzes, wire stirrers.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Using mathematics and computational thinking
Analyzing and interpreting data
Planning and carrying out investigations
Disciplinary Core Ideas
HS-PS1.B: Chemical Reactions
Energy and matter
Scale, proportion, and quantity
HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
HS-PS1-6: Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.