Pitfall of an initial rate study: On the kinetics and mechanism of the reaction of periodate with iodide ions in a slightly acidic medium

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Abstract

The kinetics of the periodate-iodide reaction has a contradictory history dating back to almost a century. This reaction has been reinvestigated spectrophotometrically in the pH range 3.13-5.55 in both buffered (acetic acid/acetate) and unbuffered solution at T = 25.0 ± 0.1 °C with an I = 0.5 M ionic strength. The spectra between 290 and 500 nm were recorded and the reaction was followed until at least 95% of one of the reactants was consumed. The stoichiometry has been found to be strongly dependent on pH, but the rate of the initial step is independent of pH within the pH range studied. An eight-step kinetic model is proposed with four fitted kinetic parameters to take all the important characteristics of the experimental curves into account. On the basis of the model, a perfect reconciliation of the previous contradictory results is presented. It is shown that the kinetic parameters obtained from the initial rate of formation of a product unavoidably leads to misinterpretation of the results in the case of a branching mechanism (and stoichiometry).

Original languageEnglish
Pages (from-to)890-896
Number of pages7
JournalJournal of Physical Chemistry A
Volume111
Issue number5
DOIs
Publication statusPublished - Feb 8 2007

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Iodides
Kinetic parameters
Stoichiometry
iodides
Ions
Kinetics
kinetics
Ionic strength
Acetic Acid
stoichiometry
ions
Acetates
dating
acetic acid
acetates
histories
metaperiodate
curves
products

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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title = "Pitfall of an initial rate study: On the kinetics and mechanism of the reaction of periodate with iodide ions in a slightly acidic medium",
abstract = "The kinetics of the periodate-iodide reaction has a contradictory history dating back to almost a century. This reaction has been reinvestigated spectrophotometrically in the pH range 3.13-5.55 in both buffered (acetic acid/acetate) and unbuffered solution at T = 25.0 ± 0.1 °C with an I = 0.5 M ionic strength. The spectra between 290 and 500 nm were recorded and the reaction was followed until at least 95{\%} of one of the reactants was consumed. The stoichiometry has been found to be strongly dependent on pH, but the rate of the initial step is independent of pH within the pH range studied. An eight-step kinetic model is proposed with four fitted kinetic parameters to take all the important characteristics of the experimental curves into account. On the basis of the model, a perfect reconciliation of the previous contradictory results is presented. It is shown that the kinetic parameters obtained from the initial rate of formation of a product unavoidably leads to misinterpretation of the results in the case of a branching mechanism (and stoichiometry).",
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AU - Horváth, A.

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N2 - The kinetics of the periodate-iodide reaction has a contradictory history dating back to almost a century. This reaction has been reinvestigated spectrophotometrically in the pH range 3.13-5.55 in both buffered (acetic acid/acetate) and unbuffered solution at T = 25.0 ± 0.1 °C with an I = 0.5 M ionic strength. The spectra between 290 and 500 nm were recorded and the reaction was followed until at least 95% of one of the reactants was consumed. The stoichiometry has been found to be strongly dependent on pH, but the rate of the initial step is independent of pH within the pH range studied. An eight-step kinetic model is proposed with four fitted kinetic parameters to take all the important characteristics of the experimental curves into account. On the basis of the model, a perfect reconciliation of the previous contradictory results is presented. It is shown that the kinetic parameters obtained from the initial rate of formation of a product unavoidably leads to misinterpretation of the results in the case of a branching mechanism (and stoichiometry).

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