Exploring Chemical Equilibrium for Alcohol-Based Cobalt Complexation through Visualization of Color Change and UV–vis Spectroscopy

• Jolie Ren ^[1] ; Tiffany Lin ^[1] ; Leonard W. SpragueIris Peng ^[1] ; Li-Qiong Wang ^[1]
  1. [1] Brown University

     Brown University

     City of Providence, Estados Unidos

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 97, Nº 2, 2020, págs. 509-516
• Idioma: inglés
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• Resumen

  • 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.