分光光度法测定指示剂解离常数的实验教学改进与实践

Improvement and Practice of Experimental Teaching for Spectrophotometric Determination of Indicator Dissociation Constant

设计了一种不需测定指示剂浓度,只需测定指示剂吸光度即可计算获得指示剂解离常数的实验教学方法。实验通过调节溶液pH,使指示剂呈现不同颜色,通过分光光度法测定了溴百里酚蓝指示剂的解离平衡常数pKa=7.24,并与文献值pKa=7.30进行了对比,结果基本一致。通过该实验学生不仅能理解指示剂的化学解离平衡,还能更好地掌握紫外-可见分光光度计的工作原理及操作方法。本实验教学将化学分析原理与仪器分析测定进行了有机结合,提出了一种采用分光光度法实现高效、简单的测定指示剂解离常数的方法,不仅增强了学生的动手能力,而且培养了学生的创新能力,提高了学生的学习兴趣。

A method is proposed to calculate the dissociation constant of the indicator without measuring the concentration of the indicator and just by measuring the absorbance of the indicator. The dissociation equilibrium constant of bromothymol blue indicator is determined to be pKa=7.24 by adjusting the pH value of the solution to make the indicator present different colors. The results are consistent with those of literature value pKa=7.30. Through this experiment, students can not only master the chemical dissociation equilibrium of indicators, but also better understand and grasp the working principle and operation method of ultraviolet-visible spectrophotometer. By organically combining the principles of chemical analysis with instrumental analysis, a simple and efficient method is successfully developed to determine the dissociation constant of indicator by spectrophotometry experiment. This method not only improves the students’ practical ability, but also cultivates their innovative ability and enhances their learning interest.