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

104 VI Simple tin aqua ions
has been selected in this review. Due to the experimental limitations, high ionic strength
and mixed background electrolyte, the ion interaction coefficient can be estimated only
crudely ε(Sn 4+ , ClO − , 298.15 K) = (0.7 ± 0.2) kg mol –1 4
.
ο
E
As indicated in the beginning of Section VI.3 selected values for
(Sn 4+ /Sn 2+ ο
) and Δ G (Sn 2+ , 298.15 K) enable selection of
f
f
m
Δ G (Sn 4+ , 298.15 K) = (46.7 ± 3.9) kJ mol –1 .
ο
m
VI.3.2 Entropy estimation methods for aqueous tin(IV) ion
As discussed in Chapter X of [1997ALL/BAN] there are several methods available to
estimate entropies of aqueous species. These methods use correlations between ionic
entropies and a combination of crystallographic radii, molar mass, molar volume,
electrical charge etc. The most reliable effective ionic radii for metal ions are listed in
[1976SHA]. Unfortunately no ionic radius can be defined for Sn 2+ , see Appendix A
entry on [1976SHA].
With Sn 4+ the situation is quite different, as pointed out in Appendix A entry on
[1951POW/LAT]. A modified Powell-Latimer correlation was based on 33
experimentally determined and comparatively reliable entropies of monatomic uni-, di-,
tri-, and tetravalent cations, see Figure VI-3.
This modified Powell-Latimer correlation led to (Sn 4+ , 298.15 K) =
− (468 ± 33) J·K –1·mol S m
–1 .
When the correlation functions suggested by [1992SAS/SHO] are applied (see
o
Appendix A) to the 33 monatomic cations, the average absolute difference ( δS m )
ο
o
between the measured and calculated S m values, δ S m = 10.23 J·K –1·mol –1 . By this
method, the partial molar entropy of Sn 4+ can be estimated to be:
ο
S m (Sn 4+ , 298.15 K) = − (472.5 ± 20.5) J·K –1·mol –1 ,
where the uncertainty has been taken twice the average value of the 33 monatomic
cations mentioned above. Although the correlation functions of [1992SAS/SHO] and
ο
[1951POW/LAT] are different, the predicted values of S (Sn 4+ m , 298.15 K) as well as
the estimated uncertainties are similar. While only experimentally determined values
ο
can be selected, S (Sn 4+ , 298.15 K) = − (472.5 ± 20.5) J·K –1·mol –1 m
is the best
estimate for this quantity obtained by this review.
ο
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012