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

IX.1 Sulfur compounds and complexes 225
299 K, s = 0.7 M at 333 K). Babko and Lisetskaya [1956BAB/LIS] report data on
solubility of very finely dispersed or colloidal SnS 2 in dependence of pH (pH = 8 to 12,
10 –5 to 10 –2 M) at 273 K. A series of solubility determinations in relatively concentrated
solutions of HCl and CaCl 2 has been performed by Topgyna and Kochetkova
[1983TOP/KOC], [1984KOC/TOP] at 298 K. On the basis of thermodynamic
modelling from the collected results, the Gibbs energy of formation of SnS 2 was
estimated to be − 180.75 kJ·mol –1 for a good crystallised product and − 172.80 kJ·mol –1
ο
for a nearly amorphous product [1984KOC/TOP]. These values of Δ (SnS 2 , s,
298.15 K) are 30 − 40 kJ·mol –1 fGm
more negative than the value of – 143 kJ·mol –1 obtained
from the data recommended in this review. The model and experimental data of
[1984KOC/TOP] are obviously not suitable for the derivation of standard
thermodynamic quantities (see Appendix A).
IX.1.2 Tin sulfates
IX.1.2.1
Aqueous sulfato complexes of tin(II)
Only two papers report equilibrium data for the SnSO 4 (aq) complex [1975WAD/ITO]
and [1981PET/MIL]. Since in the latter work the authors applied very high
2
[ SO − ]/[Sn 2+ ] ratios (up to 1.5 × 10 6 4
), they also detected the formation of a bis-complex
(Eq.(IX.10)).
Sn 2+ + SO 2−
SnSO 4 (aq) (IX.9)
4
SnSO 4 (aq) +
2
SO −
4
2
Sn(SO
4) −
2
(IX.10)
The recalculated constants for zero ionic strength – based on the published
data – are rather different (see Table IX-15). In the case of [1981PET/MIL] the
calculation is based on a few points determined with increasing concentration of the self
medium (Na 2 SO 4 ). On the other hand, [1975WAD/ITO] performed potentiometric
titrations at several ionic strengths, therefore our SIT treatment (Figure IX-5) was based
only on their values. Nevertheless, the log 10 β 1 value derived from the data of
[1981PET/MIL] at constant ionic strength (I = 1.5 M) Na(NO 3 ,SO 4 ) agrees relatively
well with the value extrapolated by using the data reported in [1975WAD/ITO] (see
filled square in Figure IX-5). It should be mentioned, that in [1975WAD/ITO] the
authors evaluated their data by assuming the formation of Sn(HSO 4 ) + as well as the
species SnSO 4 (aq). However, the SIT treatment of the data reported for the
reaction Sn 2+ 2
+ 4 SnSO 4 (aq) resulted in an unreliably high Δε value
(Δε = 0.85 kg·mol –1 ), therefore in our re-evaluation the formation of the latter species
was neglected.
SO − CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012