催化光度法测定伊文思蓝褪色反应速率常数——推荐一个物理化学新实验

Determination of the Rate Constant in Evans Blue Oxidation by Catalytic Spectrophotometry:A Recommended Physical Chemistry Experiment

介绍了一个关于复杂反应动力学测量的物理化学实验。基于亚硝酸钠作用下溴酸钾氧化伊文思蓝褪色反应,通过测量不同初始反应条件下系统吸光度随时间的变化情况,推导伊文思蓝和溴酸钾的分级数,探讨亚硝酸钠对反应的加速作用,并根据不同温度下的测量数据计算表观反应活化能。本实验可依据学时安排开设为基础性实验或综合设计性实验。两个学期的教学实践表明,作为综合设计性实验,本实验可加强学生对表观速率常数、表观活化能以及催化作用的认识,并促进学生综合实验能力的培养;此外,本实验也可适当精简后作为基础性实验项目“丙酮碘化反应”的替代方案,能克服该实验中存在的反应速率较快不易记录实验数据、碘不易清洗污染比色皿等问题。

The reaction between acetone and iodine is a typical dynamic experiment.However,students are often troubled by the failure to record sufficient experimental data.Here,a fading reaction system was introduced based on the oxidation of Evans blue by potassium bromate in the presence of sodium nitrite.The reaction was a first-order reaction for both Evans blue and bromate,while nitrite exhibited a significant catalytic effect.Based on the apparent rate constants in the absence and presence of nitrite under different temperatures,the apparent activation energy was calculated.For students,the proposed experiment helps them acquire a deeper understanding of relevant chemical kinetics knowledge and develop comprehensive experimental ability.In addition,it is also an ideal substitute for the basic experiment,i.e.,the reaction between acetone and iodine.