Reactivity of Mn III Compounds

The important reactions of Mn(III) compounds and complexes are oxidations during which the reductant is oxidised and Mn(IIl) is reduced. If the reactions are not too fast, their kinetics can be easily studied. 

Another interesting reaction is ligand replacement which may take place at a measurable rate. The process is then sometimes referred to as leaching. 

Mn203 is commercially available and is expected to oxidise Cr(lII) to dichromate in acidified solution. Since this is more strongly absorbing than Cr(III) solutions and since their spectra do not overlap, the kinetics of the reaction can be readily studied by withdrawing aliquots of a thermostatted suspension and measuring [Cr(Vl)] spectro photometrically. 

Prepare a stock solution of 0.01 M K2Cr207 solution. By successive dilution, prepare solutions of a concentration range from 0.00025 to 0.000025 M and run the spectrum of the most concentrated solution over the range 300-600 nm and locate the wavelengdi of maximum absorption. Measure accurately the absorbance at this wavelength of your prepared solutions and check the applicability of Beer s law. 

2 Leaching Mn20j with pyrophosphate solution Pyrophosphate forms a strongly coloured complex in 

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