Vanadium concentration formation constant

Unlike V(II), both the V(III) and V(IV) oxidation states are stable in water. However, neither the V(III) nor the V(IV) oxidation states are easily maintained in the presence of oxygen if the pH is neutral or above, although, under acidic conditions, both these states are rather easily maintained. Somewhat surprisingly, the V(IV) species is more readily oxidized by 02 than is the V(III) species. In aqueous acidic solution, the vanadium(III) ion exists as a hexaqua octahedral complex that can deprotonate to form the 2+ and 1+ species, dependent on pH. Additionally, di, tri and tetra polymeric forms are known. Structures have been proposed and their formation constants determined [10], The occurrence of the various polymeric forms in the presence of sulfate has also been described and is particularly relevant to concentration of vanadium by bioaccumulators [10],... 

The first term is the law observed in the absence of catalyst. The effect is dramatic, however, with associated rate constants ko and ki being 50.3 1 mol s and 3.43 x 10 1 mol s respectively, and may be ascribed to the formation of a Mo -BrOa" complex with no evidence for any change in the oxidation state of the catalyst during the course of the reaction. The kinetics and mechanism of the bromate-ascorbic acid reaction have also been reported, and the effects of phosphate on the oxidation of iodide by chlorate in the presence of catalytic concentrations of vanadium(iv) have been described, the latter systems being considered to involve vanadium(iv)-phosphate complexes. 

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