The hydrolysis of metal ions. Part 10. Kinetic and equilibrium measurements of molybdenum(VI)

Abstract

The potentiometric titration technique has been used to study molybdenum(VI) equilibria in 1.0 mol dm^–3 sodium nitrate and at 25 °C. Numerical treatment of the data indicates that the ‘best’ model includes the species [HMoO₄]^–, H₂MoO₄, [Mo₇O₂₄]^6–, [Mo₇O₂₃(OH)]^5–, [Mo₇O₂₂(OH)₂]^4–[Mo₇O₂₁(OH)₃]^3–, [Mo₈O₂₆]^4–, and [Mo₁₀O₃₄]^8– whose formation constants, log β_pq, are, respectively, 3.92, 8.09, 52.49, 57.57, 61.33, 64.96, 73.18, and 79.15. Evidence is given for the existence of a high-molecular-weight species even though computational limitations preclude its identification. A ‘slow’ region of equilibrium has also been found and its kinetics studied. The reaction mechanism is discussed; the rate constants of the forward and backward reaction, k₁ and k_–1, are 642 ± 300 dm⁶ mol^–2 s^–1 and (2.51 ± 1.00)× 10^–5 s^–1, respectively. Further evidence for the co-ordination numbers of the protonated forms of the molybdate ion is given.