POLAROGRAPHIC AND COULOMETRIC STUDIES ON AQUO IONS OF MOLYBDENUM IN 0.1 M H2SO4

Solutions containing 4 X 10(-4) M Mo(VI) in 0.1 M H2SO4 exhibited three polarographic waves. The first corresponds to reduction of Mo(VI) to Mo(V) and the second from Mo(V) to Mo(IV). The third one is due to the reduction of a dimeric Mo(V) species (Mo2O42+) to Mo(III). The dimer is formed because the Mo(V) generated at the electrode is extremely labile, undergoing dimerization. The Mo(IV) species was not isolated experimentally, and its labile formation was based on computational analysis of the second polarographic wave. This molybdenum form reacts in the presence of oxidants, and the existence of a catalytic process in the Mo(VI) + H2SO4 system was observed in the presence of nitrate. Under suitable experimental conditions the Mo(IV) form suffers a disproportionation reaction and the second polarographic wave (Mo(V) --> Mo(IV)) is kinetically controlled. The kinetic reaction is prevented at low temperatures and short drop times, and under these conditions the reduction of Mo(V) is controlled by diffusion.