Abstract:

The determination of molar mass by the freezing-point depression method is one of the classical experiments in physical chemistry. Given the existing materials and literature of physical chemistry on some content in regard to freezing point determination is not detailed enough， such as the cause of the undercooling phenomenon is short of a comprehensive， in-depth explanation； the determination of the approximate freezing point of pure solvent needs to observe ‘when there is solid precipitation’， where does the precipitation of solid appear firstly in the glass tube？ What is the morphology of the precipitated solid？ The existence of these problems will cause students trouble when operating experiments. Aiming at the above problems， the whole process of solvent solidification was filmed through experimental innovation in this paper， the specific position and morphology of solid precipitation were analyzed， and it can be concluded that it was appropriate for students to observe the solid to precipitate flocculent preferentially from the glass tube bottom during experimental operation. Through the freezing-point depression method， the details of solvent solid precipitation were observed， the molecular weight of the solute was calculated and analyzed， and reliable experimental results were obtained. In this paper， the operation details of the freezing-point depression method are deeply studied and discussed， which can effectively avoid or eliminate the problems in the experimental operation and greatly improve the experimental effect on students.

Key words: Freezing point, Freezing-point depression method, Molar mass, Physical chemistry, Experimental teaching