物理化学实验教学细节探讨——凝固点降低法测定物质摩尔质量

Discussion on Details of Physical Chemistry Experiment Teaching——Determination of Molar Mass by Freezing-Point Depression Method

“凝固点降低法测定物质摩尔质量”是物理化学实验中的经典实验之一。鉴于现有的物理化学实验教材和文献对凝固点测定部分内容描述不够细致,如过冷现象产生的原因解释不够全面、深入;纯溶剂近似凝固点测定需要观察“当有固体析出时”,析出的固体优先在玻璃管的何处出现?析出的固体呈现什么形貌?这些问题的存在,会使学生操作实验时产生困扰。本文针对上述问题,通过实验创新对溶剂凝固过程进行全程拍摄,分析固体析出的具体位置、形貌,得出学生实验操作时,应观察固体从玻璃管底部优先析出絮状物为宜;通过凝固点降低法,观察溶剂固体析出的细节,计算、分析溶质的分子量,得到了可靠的实验结果。本文对凝固点降低法操作细节深入研究与探讨,可以有效地避免或消除实验操作中出现的问题,大大提高学生实验效果。

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.