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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 12 Issue 3 (2007) pp 185-189

An Effective Way to Determine the Diffusion Coefficient Using Double-Potential-Step Chronocoulometry. An Undergraduate Physical Chemistry Laboratory Experiment

Atıf Koca,*,† Musa Üce, ‡ Ali Rıza Özkaya§ and Musa Şahin‡

† Chemical Engineering Department, Engineering Faculty, Marmara University, 34722 Kadıköy, İstanbul, Turkey,, ‡ Chemistry Department, Atatürk Faculty of Education, Marmara University, 34722 Kadıköy, İstanbul, Turkey, and § Chemistry Department, Faculty of Science and Letters, Marmara University, 34722 Kadıköy, İstanbul, Turkey.
Received June 12, 2006. Accepted April 17, 2007.

Published online: 4 June 2007

Abstract. Diffusion is a phenomenon critical to all chemical processes, and it places a formal upper limit on the rates of chemical reactions; yet, there are no simple methods for measuring diffusion coefficients in solution and for demonstrating to the student the dramatic dependence on the charge of the molecules. We propose an easy method for determining the diffusion coefficients of the electrode reaction products of a ferrocene/ferrocenium redox couple by double-potential-step chronocoulometry and demonstrate the difference in diffusion coefficients of the charged and uncharged forms of molecules. The method was applied successfully by an experiment in which the diffusion coefficients of differently charged particles associated with the ferrocene/ferrocenium redox couple were determined by double-potential-step chronocoulometry. This experiment is suitable for use in undergraduate physical chemistry laboratories to introduce students to electrochemical instrumentation, especially cyclic voltammetry and double-potential-step chronocoulometry. It is an effective way to establish various electrochemical concepts such as redox systems, electron transfer reactions, reduction potential, peak potential, peak currents, and diffusion coefficients, and to demonstrate the use of these techniques for determination of the diffusion coefficients of the products of an electrode reaction.

Key Words: Laboratories and Demonstrations; analytic chemistry; diffusion; redox reactions; electrochemistry

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Issue date: June 1, 2007

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