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Exploring Chemical Equilibrium for Alcohol-Based Cobalt Complexation through Visualization of Color Change and UV–vis Spectroscopy
Journal of Chemical Education ( IF 3 ) Pub Date : 2019-12-31 , DOI: 10.1021/acs.jchemed.9b00264
Jolie Ren 1 , Tiffany Lin 1 , Leonard W. Sprague 1 , Iris Peng 1 , Li-Qiong Wang 1
Affiliation  

Introducing chemical equilibrium concepts in undergraduate general chemistry promotes improved understanding of chemical reactions. We have developed an engaging laboratory experiment exploring the equilibrium of cobalt complexation in alcohols using UV–vis spectroscopy and successfully implemented in a large general chemistry class of 378 students at Brown University. The octahedral to tetrahedral (pink to blue) cobalt complex transition generates vivid visualizations, increasing students’ interest in learning. The equilibrium constants can be measured using UV–vis absorption spectroscopy and the Beer–Lambert law. Vast differences in molar absorptivity coefficients between octahedral and tetrahedral geometries of cobalt complexes prompt discussions on absorptivity, orbital splitting, and color change under the purview of learning Le Châtelier’s principle. Additionally, the experimental results regarding the equilibrium constant allowed students to examine possible mechanistic pathways. Student responses to conducting the experiment were positive, most notably because this experiment encouraged them to analyze their experimental results critically and propose possible reaction mechanisms and equilibrium expressions while appreciating the sharp color transition that the complexation equilibrium undergoes.

中文翻译:

通过颜色变化和紫外可见光谱的可视化探索基于醇的钴络合的化学平衡

在大学本科化学专业中引入化学平衡概念可增进对化学反应的理解。我们已经开发了一个引人入胜的实验室实验,使用紫外可见光谱研究酒精中钴的络合平衡,并成功地在布朗大学的378名大学生的普通化学课程中实施了该实验。八面体到四面体(粉红色到蓝色)钴的复杂过渡产生生动的可视化效果,从而提高了学生的学习兴趣。可以使用紫外可见吸收光谱和比尔-兰伯特定律测量平衡常数。钴配合物的八面体和四面体几何结构之间摩尔吸收系数的巨大差异促使人们对吸收系数,轨道分裂,在学习LeChâtelier原理的范围内改变颜色。此外,有关平衡常数的实验结果使学生能够检查可能的机械路径。学生对进行实验的反应是积极的,最显着的原因是该实验鼓励他们批判性地分析实验结果,并提出可能的反应机理和平衡表达式,同时欣赏络合平衡所经历的急剧的颜色转变。
更新日期:2019-12-31
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