Influence of polymerization of Mo6 on its electroreduction

Reduction of different molybdenum ions on Pt-electrode has been investigated with the aim to apply them for amperometric titration. The experiments have shown that in sulphate solutions Mo6 gives one reduction wave at a concentration of 9.8x10-2 mol. The current is proportional to molybdenum concentration within the range from 4.2x10-2 to 1.96x10-1 mol., which can be used for amperometric titration. It has been established that only polymer particles with a certain polymerization degree n reduce on Pt-electrode. From experimental data it follows that for Mo6, which does not reduce on Pt-electrode, n(<=)2; only reduction of Mo6 for which n=3 is observed. Chromatographic data have shown that, with increasing acidity and MoO42- ion-concentration, the mobility of ions decreases, i.e. polymerization grows. The process of Mo6 reduction under the conditions studied can be schematically presented as follows (without taking into account the hydration processes): Mo3O82++anti e→Mo3O8+, which means that polymer trimolybdates are reduced with the addition of one electron