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

IX.1 Sulfur compounds and complexes 227
The SIT analysis of the experimental constants reported in [1975WAD/ITO]
for Reaction (IX.9) in perchlorate media at 25 °C (Figure IX-5), resulted in the
following values
ο
log10 β
1
((IX.9), 298.15 K) = (3.43 ± 0.25)
and Δε(IX.9) = (0.11 ± 0.33) kg·mol –1 . From Δε(IX.9), the ion interaction coefficient
ε(SnSO 4 (aq),NaClO 4 (aq)) = (0.19 ± 0.35) kg·mol –1 can be calculated, which is a
relatively high value for a neutral species, however considering the uncertainty range, it
ο
is acceptable. The above log10 β
1
value is slightly higher than expected based on the
recently reviewed Pb 2+ - SO 2−
system ( log β ο = (2.72 ± 0.05), [2009POW/BRO]).
and hence
4
10 1
The selected thermodynamic formation constant, listed above, corresponds to
Δ G ((IX.9), 298.15 K) = – (19.6 ± 1.4) kJ mol –1 ,
r
ο
m
ο
ΔfG m
(SnSO 4 , aq, 298.15 K) = – (791.0 ± 1.5) kJ mol –1 .
Wada and Ito also studied the temperature dependence of complex formation
processes at I = 0.5 M and at four different temperatures between 15 and 45 °C
ο
[1975WAD/ITO]. The authors reported ΔrH m((IX.9), I = 0.5 M NaClO 4 ) =
16.9 kJ·mol –1 ο
, which can be used as tentative value for Δ H (IX.9).
r
m
IX.1.2.2
Aqueous sulfato complexes of tin(IV)
The complex formation between tin(IV) and sulfate ion has been studied by Brubaker
[1954BRU], [1955BRU], [1957BRU]. He explained the solubility of SnO 2 in 0.2 to
1.0 M H 2 SO 4 solution by Reaction (IX.11),
SnO 2 (s) + 2 H 2 SO 4
ο
2
SnSO + 2
4 + SO − 4 + 2 H 2 O(l)
ο
(IX.11)
and reported the value log10
K ((IX.11), 303.15 K) = − 1.30 and log10
K ((IX.11),
291.15 K) = − 1.55 [1955BRU]. In 1.0 to 4.0 M sulfuric acid solution Brubaker reported
2
the formation of bis-sulfato complex ( SnSO + 2
4 + SO − 4 H 2 Sn(SO 4 ) 2 (aq), K 100)
[1957BRU]. Although the existence of tin(IV)-sulfato complexes is indisputable, due to
the reasons mentioned in Appendix A, the above equilibrium constants cannot be used
to derive selected values.
IX.1.2.3
Solid tin sulfates
Anhydrous SnSO 4 can be prepared from aqueous solutions containing an excess of
sulfuric acid [1926CAR], [1960DON/MOS]. In oxygen-free atmosphere it is thermally
stable until 360 − 370 °C [1960DON/MOS]. Crystal structure analysis reveals trigonal
pyramidal coordination of tin by oxygen atoms of three different sulfate groups
[1972DON/PUX]. No evidence for a hydrated form of neutral tin(II) sulfate exists. Due
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012