The decomposition of tris-(oxalato)-manganate (III) complex ion as the reaction suitable for the laboratory practice on chemical kinetics

The complex ion [Mn(C2O4)3]3- is very photosensitive and rapidly decomposes at the daylight even at ambient temperatures. Although the mechanism of this reaction is complicated, its kinetic equation obeys the pseudo-first order. In addition, the tris-(oxalate)-manganate ion has a low thermal stability, and the reaction of its decomposition is highly affected by temperature. This makes this reaction very suitable for demonstrating the laws of chemical kinetics to the students – both the first-order reaction kinetics and the dependency of the rate constant on temperature. The kinetic studies of this reaction using a photocolourimetric method were performed; the influence of the initial concentrations of the reagents and temperature on the rate was studied. The didactic implementation of the reaction was discussed. The methodical instruction for the organization of the laboratory practice is provided. Keywords: activation energy, Arrhenius equation, chemical kinetics, decomposition, first order reaction