凝固点降低法测定摩尔质量实验试剂的改进

Improvement of Experimental Reagent for the Determination of Molar Mass by Freezing Point Reduction Method

目前在高校基础无机化学和物理化学实验课程中开设的"凝固点降低法测定相对分子质量"实验,一般选用"萘-环己烷"或"萘-苯"为溶质和溶剂。萘、环己烷、苯均是致癌物质,污染环境,严重伤害实验教学人员的身体。用"蔗糖-水"或者"尿素-水"替代"萘-环己烷"或"萘-苯"可消除环境污染;对常用的通过凝固点降低法来测定相对分子质量的实验试剂进行更改替换,选用水作溶剂测定尿素的摩尔质量,解决了环保问题。研究了水+尿素体系的步冷曲线,确定了水和尿素水溶液的凝固点值。改进后的试剂尿素取用方便,测定其摩尔质量相对误差可以控制在1%左右。

At present, in the course of basic inorganic chemistry and physical chemistry experiment in universities, the method of ＂freezing point reduction＂ to determine molar mass usually adopts ＂naphthalene-cyclohexane＂ or ＂naphthalene-benzene＂ as solute and solvent. Naphthalene, cyclohexane and benzene are carcinogenic substances that can pollute the environment and seriously injure the body of experimental teaching staff. ＂Sugar water＂ or ＂urea water＂ instead of ＂naphthalene cyclohexane＂ or ＂naphthalene benzene＂ can eliminate environmental pollution. In this paper, the common method of freezing point reduction for the determination of the molar mass of organic compounds was improved. The molar quality of urea was determined with water as solvent, and the environmental problems were solved. The step cooling curve of water ＋ sucrose system was studied, and the freezing point of water solution was determined. The urea as improved reagent is convenient to be used, and the relative error of its molar mass can be controlled about 1%.