Collect. Czech. Chem. Commun. 1990, 55, 2898-2903
https://doi.org/10.1135/cccc19902898

Kinetics of guyard's reaction with regard to permanganate chemical oscillators

Marta Mrákavová and Łudovít Treindl

Department of Physical Chemistry, Comenius University, 842 15 Bratislava

Abstract

Phosphoric acid is a necessary component of permanganate chemical oscillators. When Mn(II) ions are present in a stoichiometric excess, the reaction is of first order with respect to the concentration of MnO4- ions and of fractional order with respect to the concentration of Mn(II). When MnO4- ions are in a stoichiometric excess, the reaction is autocatalytic in nature and the inflexion time increases linearly with the concentration of H3PO4; analysis of the sigmoidal curve gave the rate constant of the non-catalytic step, k1, and that of the catalytic step, k2, which is indirectly proportional to the concentration of H3PO4. The probable mechanism of the Guyard reaction involves a reversible equilibrium between Mn(IV) and colloidal MnO2 and subsequent coagulation to form a MnO2 suspension. Similarly to permanganate chemical oscillators, phosphoric acid or its ions play the key role, since they stabilize the colloidal MnO2 which serves as a reservoir of Mn(IV) ions.