Hello and welcome to physical chemistry laboratory. Today's topic, cryoscopy. We want to determine the molar mass of a solute by measuring the freezing point of the solution. The following setup is needed to carry out the experiment.

A precision balance, a digital thermometer, an XT recorder, test tubes for solutions of different concentrations, an ice bath thermometer, a dewar flask on a magnetic stirring plate. For the cold bath, mix 300 milliliters of water with about 60 grams of table salt in the dewar flask.

Slowly add ice until the cold bath reaches a temperature of negative 7 degrees Celsius. Test tubes are filled with stock solution and equipped with a small magnetic stir bar. Ideally, the solutions are prepared on the balance. The XT recorder is connected to the temperature measuring instruments.

The reference thermometer is positioned in a second dewar flask filled with the melting ice. The test tubes are hung one after the other in the cold bath. Check whether the stir bars move freely.

The temperature probe is placed in the center of the test tube. The temperature of the solution will begin to drop to below its freezing point. Only after the first crystals form, temperature will rise to the constant freezing point. The XT recorder picks up this temperature time curve. Make sure you always record the isothermal crystallization level of each solution.

The crystallization of the solution can be detected not only with the recorder, but also seen with the naked eye. Determine the freezing point of pure water both before and after the measurements of the solutions. More information about the experiment and especially its evaluation can be found in the textbook and in the handout.

Good luck in the lab and thanks for watching!