Study of Mo(3) complexing in hydrochloric acid solution by the oxidation potential method

The existence of a reversible redox Mo(3)/Mo(5) system makes it possible to study the complex formation of Mo(3) and Mo(5) with chloride-ions in a wide range of their concentrations. The complex formation was studied by measurements of electromotive force of the Galvani element, described. The Mo(3) and Mo(5) concentrations in the element were equal to each other and equalled 1x10-3M. The ionic power of the solution was 3.0, the HCl concentration ranged from 4x10-2 to 1.0 M, and that of acetic acid varied from 3.0 to 2.0 M respectively. Increase in HCl concentration leads to the Mo(5)/Mo(3) system potential growth. It is shown that under these conditions the [Mo(OH)Cl4]2- complex is formed, with the concentration stability constant β=400+-200