Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

VII.1 Aqueous tin hydroxido complexes 109
For Reaction (VII.2) remarkably consistent equilibrium constants are available
for I = 3 M NaClO 4 , but conflicting data were published for lower ionic strengths. The
constants reported in [1939GOR], [1941GAR/HEI] and [1952VAN/RHO] were rejected
for reasons mentioned in Appendix A. Only the data reported by Pettine et al. can be
* ο
used to determine the ionic strength dependence of log10 β
1,1
. However, these
measurements were conducted in NaNO 3 media, and Andreev et al. [1980AND/SAM]
reported the formation of weak nitrato complexes of tin(II). Under the experimental
conditions applied in [1981PET/MIL] such species were not detected by the authors.
Moreover the experimental data reported by Pettine et al. cannot be re-evaluated
correctly by considering the formation of nitrato complexes (see Appendix A).
2−x
Therefore, the presence of Sn(NO 3)
x complexes were ignored in the re-evaluation
performed by the reviewers, but the uncertainties of the resulting constants were
increased, due to their possible presence. The extrapolation of the recalculated constants
to zero ionic strength (Figure VII-1), assuming negligible variation between 20 and
25 °C, resulted in the selected value
log
β ((VII.2), 298.15 K) = − (3.53 ± 0.40).
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10 1,1
Figure VII-1: Extrapolation of the equilibrium constants for reaction Sn 2+ + H 2 O(l)
SnOH + + H + recalculated from the data measured in NaNO 3 media [1981PET/MIL].
The data for 3 M NaClO 4 () were not included in the regression.
0
Sn 2+ + H 2
O(l) SnOH + + H +
-1
log 10 * β 11
+ 2D – log 10
a w
-2
-3
-4
-5
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
I / mol·kg –1
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012