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

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XI Group 14 compounds and complexes
For reasons mentioned in Appendix A, the constants reported in
[1976SAM/LYA] were not considered in this review. The re-evaluation of the
potentiometric data of [1961GOL/OGN] determined at 293.15 K indicated that the
consideration of two species (SnSCN + and Sn(SCN) 2 (aq)) is sufficient to describe the
experimental data up to 20% replacement of the background electrolyte (at higher
thiocyanate concentrations a notable medium effect may arise). The temperature
correction to 298.15 K is assumed to be negligible. The constants for Reaction ((XI.1),
q = 2 and 3) reported in [1980FED/BOL] were not considered, since these reactions
take place in a region where an important medium effect can be expected. Similarly, the
value of log 10 β 1 reported in [1980FED/BOL] for I = 0.5 M was rejected, as the amount
of SnSCN + formed up to [SCN – ] tot = 0.1 M (20% replacement of the background
electrolyte) is probably too small to produce a reliable value.
The SIT analysis of the remaining 3 values (Figure XI-1) resulted in the
following selected constant
ο
log10 β
1
((XI.1), q = 1, 298.15 K) = (1.5 ± 0.7).
The corresponding ion interaction coefficient is Δε((XI.1), q = 1) = − (0.07 ± 0.29)
kg·mol –1 .
Figure XI-1: Extrapolation to I = 0 of the experimental data for reaction Sn 2+ +
SCN – SnSCN + in NaClO 4 media. Experimental data from [1961GOL/OGN] and
[1980FED/BOL].
3.0
2.5
Sn 2+ + SCN – SnSCN +
2.0
log 10
β 1
+ 4D
1.5
1.0
0.5
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
I / kg·mol –1
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012