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  Home > JCE Print > Journal of Chemical Education > Issues > 1997  > May  >
In the Laboratory
Ionic Strength Effect on the Rate of Reduction of Hexacyanoferrate(III) by Ascorbic Acid: A Flow Injection Kinetic Experiment
Joanquim A. Nobrega and Fabio R. P. Rocha
Departamento de Quimica, Universidade Federal de Sao Carlos, Caixa Postal 676, 13.560-270 Sao Carlos, SP, Brasil
Cover
May 1997
Vol. 74 No. 5
p. 560
Abstract
Flow injection analysis (FIA) is a well recognized tool for solutions management. In spite of the use of this technique mainly for quantitative determination of analytes in solution, FIA systems can also be used for obtaining physical chemistry data. This work describes the use of a flow diagram to perform a kinetic experiment: the effect of ionic strength on the rate of reduction of hexacyanoferrate(III) by ascorbic acid. The rate determining step of this reaction involves the collision between two anionic species. The increase of the ionic strength of the medium alters the ionic atmosphere and changes the charge densities around the anions. Consequently, there is an increment of the rate constants for higher ionic strengths. In the proposed system, the flow is stopped by commutation when the center of the sample zone attained the flow cell and a gradual decrease in signal, related to the redox reaction, is registered as function of time. This allowed the determination of the rate constants as a function of the ionic strength. The product of the charges of the ions involved in the rate determining step was estimated in 3.2 that is close to the expected value considering the proposed mechanism.
More Information
*  Citation
 Nobrega, Joaquim A.; Rocha, Fabio R.P. . J. Chem. Educ. 1997 74 560.
*  Keywords
 Analytical Chemistry, Physical Chemistry, Kinetics, Redox Reactions, Time-Dependent Reactions, UV-Vis Spectroscopy
*  History
 Created:
Last Updated:		 July 28, 1999
June 23, 2005
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