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

186
VIII Group 17 (halogen) compounds and complexes
Δ G ((VIII.11), q = 4, 298.15 K) = − (54.6 ± 1.8) kJ mol –1 ,
r
r
ο
m
Δ G ((VIII.11), q = 5, 298.15 K) = − (62.3 ± 2.3) kJ mol –1 ,
r
ο
m
Δ G ((VIII.11), q = 6, 298.15 K) = − (56.1 ± 2.8) kJ mol –1 .
ο
m
VIII.3.3 Aqueous bromide complexes
VIII.3.3.1 Aqueous Sn(II) bromides
Experimental equilibrium date on the bromide complexes of tin(II) obtained from
potentiometric [1928PRY], [1952VAN], [1969FED/BOL], [1975FED/BOL],
[1976SAM/LYA], kinetic [1951DUK/PIN] and voltammetric [1981PET/MIL]
investigations are reported for the following reactions
Sn 2+ + q Br – SnBr
2−q
q
(VIII.13)
The formation of six bromido complexes (q = 1 to 6) was reported in
[1969FED/BOL]. However, the re-evaluation of the experimental data reported in
[1969FED/BOL] indicated, that up to I = 4 M the potentiometric data can be well
reproduced considering the formation of the species SnBr + , SnBr 2 (aq) and SnBr − 3 . At
higher ionic strength (I > 4 M) higher excess of bromide over tin(II) can be achieved,
2
4
therefore a further complex ( SnBr − ) should be also taken into account. The
experimental data of Prytz [1928PRY] and Vanderzee [1952VAN] were also
re-analyzed, while the constants reported in [1976SAM/LYA] and [1981PET/MIL]
were not considered in this review (see Appendix A). The formation constants
determined for 25 °C and I ≤ 6 M were extrapolated to zero ionic strength using
the SIT. The weighted linear regression of the eigth available data for SnBr + (Figure
VIII-26), resulted in the following selected values
ο
log10 β
1
((VIII.13), q = 1, 298.15 K) = (1.33 ± 0.18)
and Δε((VIII.13), q = 1) = – (0.10 ± 0.05) kg·mol –1 . From the latter value, the ion
interaction coefficient ε(SnBr + , ClO − 4
) = (0.15 ± 0.07) kg·mol –1 is calculated.
The SIT treatment (Figure VIII-27 and Figure VIII-28) of the accepted
formation constants for the Reactions ((VIII.13), q = 2 and 3) resulted in the selected
values:
and
ο
log10 β
2
((VIII.13), q = 2, 298.15 K) = (1.97 ± 0.21)
ο
log10 β
3
((VIII.13), q = 3, 298.15 K) = (1.93 ± 0.27).
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012