We describe in detail a re-invention of the traditional solid-liquid phase diagram experiment as a guided inquiry experience called “How does the composition of a mixture affect its freezing point?”  This POGIL-PCL (Process Oriented Guided Inquiry Learning - Physical Chemistry Laboratory) experiment follows two learning cycles. The experiment is carried out using lauric acid and stearic acid in place of biphenyl and naphthalene. These fatty acids are safer, less expensive, and cleaner, and  fatty acid mixtures have been suggested as phase-change materials for energy conservation. The experiment begins with a prediction by the students as to the freezing point of two specific mixtures of the fatty acids. Students then measure the freezing points and assess their predictions. In a second learning cycle, students make further predictions regarding the dependence of freezing point on mixture composition, select the appropriate mixtures to test their predictions, measure the freezing points, and analyze their data to construct the full phase diagram and obtain the enthalpies of fusion of the two fatty acids.  In this experiment students practice hypothesis testing, experimental design, and model building while learning content and unlearning misconceptions. We will present typical student results and discussion for these experiments.

Guided inquiry solid-liquid phase diagram experiment

249th National Meeting (2015)

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