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  Home > JCE Print > Journal of Chemical Education > Issues > 2003  > October  >
In the Laboratory
A Fluorometric Approach to Studying the Effects of Ionic Strength on Reaction Rates: An Undergraduate Steady-State Fluorescence Laboratory Experiment
Stephen W. Bigger and Peter J. Watkins
School of Molecular Sciences, Victoria University of Technology, Werribee Campus, Melbourne, 8001, Australia

Bruce Verity
School of Chemical Technology, University of South Australia, Mawson Lakes, 5095, Australia
Cover
October 2003
Vol. 80 No. 10
p. 1191
Abstract
A simple, steady-state fluorescence experiment is described in which the dynamic quenching of the quinine dication fluorescence by Cl- and Br- is studied. Solutions of sufficiently low ionic strength enable ionic activities to be taken into account by means of the Debye–Hückel equation. The experiment demonstrates how the rate of a reaction depends on the ionic strength of the medium. The experiment represents a unique example of the application of the Debye–Hückel equation without the use of simplifying assumptions regarding the calculation of ionic activity coefficients. The experiment also shows how the observed decrease in the Stern–Volmer rate constant with increasing ionic strength can be quantitatively modeled to determine the relative efficiencies of Cl- and Br- fluorescent quenching of quinine.

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Instructions for the students and notes for the instructor are available.
*  Contents JCE2003p1191W.doc (Microsoft Word)
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More Information
*  Citation
 Bigger, Stephen W.; Watkins, Peter J.; Verity, Bruce. J. Chem. Educ. 2003 80 1191.
*  Keywords
 Fluorescence Spectrometry; Kinetics; Laboratory Instruction; Luminescence; Photochemistry; Physical Chemistry
*  History
 Created:
Last Updated:		 September 2, 2003
February 28, 2005
Link to Featured Molecules added (April 2004).
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