Spectrophotometric kinetic study of formation of .beta.-12-molybdosilicic acid

Microelectrode procedures for the determination of silicate and phosphate in waters – fundamental studies

“…The reaction of phosphate with molybdate is significantly faster and in order to obtain reliable data using this steady state microdisk technique, it is necessary to work at temperatures<288 K. The results were then of a similar form and data as a function of pH and temperature are also reported in Table 1. The values for the rate constants for the formation of both molybdophosphate and molybdosilicate complexes are comparable with the limited amount of data determined spectrophotometrically in earlier articles [29,301. The rate constants for the formation of the two complexes clearly show a different dependence on pH.…”

Spectrophotometric and stopped-flow reaction-rate study of the formation of 10-molybdo-2-vanadophosphoric acid

“…We suggest that, at the acidity and V(V) concentrations used in this study, H2V206 or H3V206+ may be the predominate vanadium species in solution. A single mechanism is proposed which satisfactorily accounts for all the data, and is consistent with mechanisms that have been proposed for the formation of 12-molybdophosphoric and 12-molybdosilicic acids (24,26).…”

“…It is unfortunate that so little is known about the exact nature of Mo(VI) and V(V) in acidic solution. Previous studies (23)(24)(25)(26) along with our stoichiometry data indicate that Mo(VI) exists as a dimer in moderately acidic solution, and while the proposed structures Mo206 or 2 6+ seem reasonable, more direct chemical evidence would be reassuring. While data on the composition of Mo(VI) in moderately acidic solution is scarce, similar information about V(V) is almost non-existent.…”

“…Recent stoichiometry and reaction-rate studies of 12-MPA and 12-molybdosilicic acid (12-MSA) have been successful in determining the basic mechanism by which these compounds are formed and have provided some additional information about the nature of Mo(VI) in highly acidic solutions (23)(24)(25)(26)(27). Stoichiometry studies have shown that Mo(VI) is primarily dimeric in strongly acidic solutions (23,26,28) and this dimer has also been determined to be the reactive species (24). Thus, it has been postulated that 12-poly complexes are formed by successive reaction of phosphate or silicate with six Mo(VI) dimers.…”

Zur Bildungskinetik der ß‐Dodekamolybdatokieselsäure. 1. Die Umsetzung von monokieselsäure mit Molybdänsäure

“…Wird das pH der Losung variiert, so lndern sich in Ubereinstimmung mit HARGIS [14] im Bereich von pH = 1,4-2,l weder die Reaktionsordnung in Bezug auf SiO, noch die Reaktionsgeschwindigkeit. Steigt der pH-Wert der Losung uber pH = 2 , l an, so nimmt die Reaktionsgeschwindigkeit ab, die Reaktion gehorcht aber bis pH = 3,l weiter einem Geschwindigkeitsgesetz erster Ordnung.…”