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

VII.1 Aqueous tin hydroxido complexes 111
Sn 2+ + 3 H 2 O(l) Sn(OH) − 3
+ 3 H + ; * β
3,1
(VII.5)
In the neutral pH range Sn(OH) 2 is the main species, which has very low solubility. The
only reliable solution equilibrium study concerning this complex is reported by Pettine
et al. [1981PET/MIL] using a very low tin(II) concentration ([Sn 2+ ] tot = 5.4 × 10 –7 M).
As mentioned above, the graphical data reported in [1981PET/MIL] were re-evaluated
by the present review, neglecting the possible presence of nitrato complexes. The SIT
analysis of the recalculated formation constants (Figure VII-3), assuming the
temperature correction to 25 °C negligible, resulted in the selected value:
* ο
log10 β
2,1
((VII.4), 298.15 K) = − (7.68 ± 0.40)
and Δε((VII.4), NaNO 3 ) = − (0.31 ± 0.60) kg·mol –1 .
Figure VII-3: Extrapolation of the equilibrium constants for reaction Sn 2+ + 2 H 2 O(l)
Sn(OH) 2 (aq) + 2 H + recalculated from the data measured in NaNO 3 media
[1981PET/MIL].
-4
-5
Sn 2+ + 2H 2
O(l) Sn(OH) 2
(aq) + 2H +
log 10
*
β12 + 2D – 2log 10
a w
-6
-7
-8
-9
-10
0.0 0.5 1.0 1.5 2.0 2.5 3.0
I / mol·kg –1
Five reliable reports are available for the equilibrium constant of
Reaction (VII.5). The primary data related to the alkaline dissolution of SnO(s) reported
in [1941GAR/HEI] have been re-evaluated for the purposes of this review using the
* ο
SIT, which resulted in log K = (4.46 ± 0.01) for the reaction (VII.6):
10 3
−
−
Sn(OH)
2(aq) OH Sn(OH) 3
+ (VII.6)
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012