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

A Discussion of selected references
323
Table A-22: Composition of tin(II) hydroxide oxide [1968HOW/MOS].
Composition Sn 3 O(OH) 2 Sn 5 O(OH) 4 [1961DON/MOS]
w(SnO) 95.73% 94.92%
w(H 2 O) 4.27% 5.08%
[1968HSE/REC]
The authors prepared a new Ag 2 S based membrane electrode to determine the sulfide
ion concentration in aqueous solutions. The authors characterised the electrode, and
then used it to determine the equilibrium constants for reaction
in 0.1 M NaNO 3 solution.
SnS 2 (s) + S 2–
2
SnS −
3
(A.38)
The electrode showed excellent sensitivity, but due to the high uncertainty of
the first protonation constant of sulfide ion, the calibration of the electrode is
questionable. Using log10 K 1 = 14.44 for the first protonation constants of sulfide ion,
ο
the authors determined log10 K s,0
= − 50.83 for the solubility product of Ag 2 S. In
ο
[1989GAM/BAR], the authors recalculated the earlier reported log10 K s,0
values for
ο
Ag 2 S, and determined log10 K s,0
= − 54.7, using log10 K 1 = 18.57 and log10 K 2 = 6.99
ο
for the protonation constants of sulfide ion. Considering this log10 K s,0
value, it is
possible to recalibrate the electrode used in [1968HSE/REC]. In this way, however, the
experimental data reported in [1968HSE/REC] result in negative concentrations for the
2
dissolved SnS −
3 below pH 9. Refinement of the first protonation constant of sulfide
ion, to obtain a coherent equilibrium constant for Reaction (A.38) for all experimental
points, resulted in log10
K ((A.38), 298.15 K) = (9.1 ± 0.1), log10 K 1 = 18.19, and is an
excellent fit to the experimental data. The first protonation constant of sulfide ion
determined in this way agrees well with the currently accepted thermodynamic value
ο
( log10 K 1 = (19.0 ± 2.0)), while log 10 K ((A.38), 298.15 K) is similar to that
re-evaluated from the data reported in [1956BAB/LIS]. Due to the high uncertainty of
the first protonation constant of sulfide ion, the reviewers assigned a considerably
higher uncertainty to log10
K ((A.38), 298.15 K) (± 2.0, see Table IX-1). Therefore,
these reviewers prefer not to select a thermodynamic equilibrium constant for Reaction
(A.38) based on these reports (see also the comments on [1956BAB/LIS]), but the
recalculated values can be used until more data will be published on this system.
[1969CAR]
Electrophoretic measurements were carried out to study, among others, the complex
formation between tin(II) and chloride ion at 25 °C. The author determined the
migration of tin(II) as a function of the HCl concentration. The results indicated the
formation of three complexes (SnCl + , SnCl 2 (aq) and SnCl − 3
) up to [HCl] tot = 0.9 m.
From the curve of the mobility the following constants were derived: log10 β 1 = 1.05,
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012