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A Simple Undergraduate Concentration Step Experiment

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John Cassidy , Fiona Fitzpatrick and Sean Culhane

Department of Chemistry, Kevin Street, Dublin Institute of Technology, Dublin 8, Ireland

J. Chem. Educ., 1997, 74 (8), p 964

DOI: 10.1021/ed074p964

Publication Date (Web): August 1, 1997

Abstract

This experiment is designed to demonstrate the process of diffusion; movement of species under a concentration gradient. By using a solvent immiscible with water containing a chelate (dithizone) which changes color when complexed with a metal, in contact with an aqueous solution of zinc ions, it is possible to mimic a concentration step at the solvent water interface. It is possible to spectroscopically monitor the system if the layers are in a cuvette in a visible spectrometer. Experimentally it can be seen that the absorbance changed with the square root of time, from which the diffusion coefficient of the dithizone may be determined