A visual thinking, evidence-based, kinetic laboratory experiment: Determining the rate law for the bleaching of crystal violet dye by hydroxide ions

• S. Losada-Barreiro ^[1] ; C. Bravo-Díaz ^[1] ; A. Peña-Gallego ^[1] ; R.A. Mosquera ^[1] ; A.M. Graña ^[1]
  1. [1] Universidade de Vigo

     Universidade de Vigo

     Vigo, España

     
• Localización: EDULEARN20 Proceedings: 12th International Conference on Education and New Learning Technologies (July 6th-7th, 2020, Online) / coord. por Luis Gómez Chova, A. López Martínez, I. Candel Torres, 2020, ISBN 978-84-09-17979-4, págs. 3017-3021
• Idioma: inglés
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• Resumen

  • The use of visual resources (diagrams, schemes, etc.) to understand chemical concepts and to communicate them aims to favor the understanding of concepts that are necessary as much higher order skills and to spatially organize contents. This is particularly important in chemistry, since chemists are always interested in explaining how matter is transformed from “reactants” to “products”, i.e., how chemical reaction takes place and how we can control it either to increase the rate of the reaction or to inhibit it.Students often have trouble deciding how to assemble their knowledge coherently to solve an unfamiliar multicomponent problem and visual thinking can be used as an useful tool to visually structuring the fundamental elements of the chemical process. The mechanisms of reactions are always shown as schemes or diagrams where one starts with the reactants to end up with the products indicating all intermediate steps and the proposed rate law, which is a mathematical equation that relates the rate of the reaction with the concentrations of reactants, must be consistent with the proposed mechanism.Here we propose a “hands-on” chemical kinetics experiment, based on visual thinking techniques, aimed to make undergraduates’ education more accessible and more enjoyable by means of evidence-based educational laboratory practices based on a rigorous chemical content. The particular proposed experiment, the kinetics of crystal violet dye bleaching, is aimed to make students to understand the step-by-step transformation of reactants to products. All these elementary steps provide the mechanism by which the reaction proceeds, which should detail the formation and disappearance of any intermediate in the course of the reaction.Questions in which students are asked to predict the products of reactions because these are authentic problems that require a range of knowledge and skills to solve are also proposed.