Understanding Electrophoresis through the Investigation of Size, Shape, and Charge of pH Indicators

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• 作者：Ryan K. Brenner ; Kenneth R. Hess ; Jennifer L. Morford
• 刊名：Journal of Chemical Education
• 出版年：2015
• 出版时间：October 13, 2015
• 年：2015
• 卷：92
• 期：10
• 页码：1705-1708
• 全文大小：194K
• ISSN：1938-1328

文摘

A laboratory experiment was designed for upper-level students in a Chemical Analysis course to illustrate the theoretical and practical applications of 0.8% agarose gel electrophoresis and to reinforce an understanding of weak acids/bases using easy-to-visualize pH indicators. The careful choice of indicators included acid and base types with amphiprotic intermediates, species that become either singly or doubly deprotonated, and molecules with molecular weights that span from 269 to 670 g/mol. Students measure the rate of migration of the pH indicators relative to the rate of migration of a red dye standard. The relative rates are interpreted with respect to the indicators鈥?fractions of deprotonation (and resulting molecule charges), molecular weights, and shapes. This procedure occurs under acidic (pH 4.0) and basic (pH 7.5) conditions with lower and higher applied voltages to understand the impact of changing protonation/deprotonation. This experiment has been successfully completed by over 200 analytical chemistry students with consistent results. Overall, this procedure teaches students to evaluate the controls on molecule movement in an electrical field critically, while gaining insight into weak acid/base equilibria.