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

414
A Discussion of selected references
2−q
the reactions SnClq
+ Cl – 1−q
SnClq+ 1
(q = 0, 1, 2, 3) were also derived from the
temperature dependence of the thermodynamic formation constants. It was concluded
that tin(II) chlorido complexes could be important in the transport and deposition of tin
by hydrothermal ore solutions of moderate to high salinity. The extended Debye-Hückel
equation used by the authors to calculate the individual ion activity coefficients is not
strictly identical with that applied in the SIT, therefore an uncertainty of ± 0.3 has been
assigned to the log10
β ο
q
values reported for 25 °C. The values of ln β q values for the
stepwise formation SnCl + , SnCl 2 (aq) and SnCl −
3
as a function of temperature were fitted
to the equation
ln K q = A + B(T/K) + C(T/K) 2
(A.87)
where T is in Kelvin. The values that best fit the temperature variation of each
equilibrium constants are given in Table A-70.
Table A-70: Coefficients in Eq. (A.87) to define the stepwise equilibrium constants of
SnCl + , SnCl 2 (aq) and SnCl − 3 with temperature up to 598.15 K.
A B C
ln K° 1 = ln β° 1 4.1523 – 5.9524 × 10 –3 1.0187 × 10 –5
ln K° 2 3.7022 – 1.4290 × 10 –2 2.6030 × 10 –5
lnK° 3 7.3819 – 4.1145 × 10 –3 5.7661 × 10 –5
The equations describing the temperature variation of the stepwise equilibrium
ο
constants were differentiated to give Δ
rHm
for the formation of SnCl + , SnCl 2 (aq) and
SnCl − at different temperature (see Table VIII-19).
3
[2001PER/HEF]
A detailed investigation of the Pb(II)/OH- system has been made in NaClO 4 media
at 25 °C. Combined UV-vis spectrophotometric-potentiometric titrations at
[Pb(II)] T ≤ 10 μM using a long path length cell detected only four mononuclear
*
hydroxido complexes. The values of log10 β
1q
, for the equilibria Pb 2+ + q H 2 O(l)
2−q
Pb(OH)
q
+ q H + , were – 7.2, – 16.1, – 26.5, and – 38.0 for q = 1 to 4, respectively, at
ionic strength I = 1 M (NaClO 4 ). Similar results were obtained at I = 5 M (NaClO 4 ). No
evidence was found for higher order complexes (q > 4) even at very high [OH – ]/[Pb(II)]
ratios, nor for polynuclear species at [Pb(II)] T ≤ 10 μM. Measurements using
207Pb-NMR and Raman spectroscopies and differential pulse polarography (DPP)
2−q
provided only semiquantitative confirmation. The mononuclear Pb(OH)
q
(aq)
complexes are the only hydrolyzed species likely to be significant under typical
environmental and biological conditions.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012