Tungsten(VI) equilibria: a potentiometric and calorimetric investigation
- 1 January 1987
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 7,p. 1701-1705
- https://doi.org/10.1039/dt9870001701
Abstract
Tungsten(VI) equilibria has been investigated in the range pH 5–7.8 (corresponding to a degree of protonation, Z 1.2) by potentiometric and enthalpimetric titrations at 25 °C in 1.0 mol dm–3 NaCl. The potentiometric data were treated with the computer program SUPERQUAD to examine a large number of reaction models. The model that gave the best fit to the data comprises [WO4]2– and the four polyions [W6O20(OH)2]6–, [W7O24]6–, [HW7O24]5–[H2W12O42]10– with formation constants log β6,6= 49.01, log β7,8= 65.19, log β7,9= 69.96, and log β12,14= 115.38. The enthalpy and entropy changes for the formation of the polyions were calculated from the enthalpimetric data using these constants. The enthalpy values are ΔH 6,6=–231, ΔH 7,8=–333, ΔH 7,9=–328, and ΔH 12,14=–542 kJ mol–1. The energetics of condensation is discussed in terms of the thermodynamid quantities for heptatungstate and heptamolybdate.Keywords
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