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

Abstract

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 Chatelier'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.

Fabricating a Low-Cost, Simple, Screen Printed Paper Towel-Based Experimental Device to Demonstrate the Factors Affecting Chemical Equilibrium and Chemical Equilibrium Constant, Kc

“…An absorbance− concentration calibration plot was established and used as a measure of the CoCl complex concentration can be obtained as assumed concentrations where the obtained concentrations of products at equilibrium can be acceptable for K c determination. 35 The determination of K c on PTED using a smartphone camera coupled to ImageJ software is also expected to be the inspired platform for the development of other interesting chemical equilibrium reactions, such as the formation of an iron [Fe(III)] thiocyanate complex reaction.…”

Strategies, Practice and Lessons Learned from Remote Teaching of the General Chemistry Laboratory Course at Brown University

“…The general chemistry laboratory course is considered a difficult course to teach, due to students’ heterogeneous chemistry backgrounds and learning levels. Considerable effort has been devoted to improving laboratory courses through the development of engaging experiments that are applicable to students’ daily life. − As a result, these laboratory experiments significantly enhanced student learning and stimulated their interest in science. Despite these engaging laboratory experiments, students with little or no experience with chemistry laboratories continue to struggle in the course.…”

“…Brown University’s laboratory curriculum normally includes 7–8 weeks of laboratory experiments created by our students and faculty. Students who have already completed the course have collaborated with faculty to create several engaging experiments that meet students’ learning levels and relate chemistry to daily life. − For example, the fuel cell lab relates electrochemistry and thermodynamics to the clean energy, and the acid-rain lab links acid–base chemistry to acid rain in the environment . Our experiments also utilize color observed in visual art, such as medieval stained glass, textiles, and gemstones, to facilitate the discussion of quantum mechanics, molecular structures, and chemical bonding…”

Introductory Chemistry Laboratory: Quantum Mechanics and Color

“…This laboratory experiment was developed through a collaborative effort among faculty and graduate and undergraduate students at Brown University, and it has been successfully implemented in classes of over 600 students (mostly of first-year students) per academic year for over three years. Involving UTRA (Undergraduate Teaching and Research Award) undergraduates − in the development process allowed us to create an experiment that is at the appropriate skill and knowledge level of our introductory chemistry students, promoting academic engagement. This simple engaging laboratory can be adapted to a high school and to other undergraduate curricula, relating chemistry to color with or without introducing advanced topics, depending on students’ learning levels.…”