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

336
A Discussion of selected references
entropies, Gibbs energy function and vapour pressure. Recommended data are tabulated
in the temperature range 0 to 3000 K.
[1973KLI/BAR]
The solubility of synthetic cassiterite (SnO 2 ) in pure water at 25, 100, 200 and 300 °C,
and in 0.05 to 0.5 M NaOH solutions at 200 °C was studied using an autoclave. The
equilibrium between the solid and solution phases was established within 20 days at
100 °C, and within ten days at 200 °C. The dissolved tin(IV) was determined
colorimetrically using phenylfluoron and p-nitrophenylfluorone. The detection limit,
reported by the authors, is 0.08 μg·ml –1 tin(IV) (in [1970BAR/KLI] 0.5 μg·ml –1 is given
for the same method). The experimental data indicated only formation of the complex
2
6
Sn(OH) − . The solubility of SnO 2 both in water and in alkaline solutions (as compared
to the data reported in [1970BAR/KLI]) increased with increasing temperature. From
ο
the measured solubility at different temperatures Δ
rH
m
= 14.3 kJ·mol –1 was determined
for the enthalpy of reaction SnO 2 (s) + 2 H 2 O(l) Sn(OH) 4 .
*
Using the log10 β
q,1
(q = 1 to 4) values reported in [1971NAZ/ANT] for
I = 1.0 M NaNO 3 and the Vasil'yev coefficient (b) determined for the hydrolysis of
Ge(IV), the authors calculated the thermodynamic hydrolysis constants of tin(IV), by
* ο
* ο
means of the SIT related Vasil'yev equation: log10 β
1,1
= 0.49, log10 β
2,1
= 0.30,
log β = − 0.58, log β = − 2.61.
log
* ο
10 3,1
* ο
10 4,1
Since even the original data of [1971NAZ/ANT] are only estimates, the above
β values cannot be accepted.
*
10 q,1
The solubility data determined in NaOH solution at 200 °C have been
re-evaluated for the purposes of this review, using pK w = 11.2 for I = 0 and T = 200 °C.
The non-linear curve fitting of the data points resulted in the following constants:
* ο
2
log10 K
s,0
= − (5.52 ± 0.06), log10 β
6,1
(Sn(OH) 4 + 2 H 2 O(l) Sn(OH) − 6
+ 2 H + ) =
2
− (20.16 ± 0.09), and Δε(Sn(OH) 4 + 2 H 2 O(l) Sn(OH) − 6
+ 2 H + , NaOH) =
− (0.81 ± 0.17) kg·mol –1 (see Figure A-32). Since the determined solubility of SnO 2 in
alkaline solutions at 200 °C is lower than can be expected from the values selected in
this review at 25 °C, the above constants can be regarded only as estimates.
[1973MIK]
Mikler [1973MIK] measured the enthalpy change at 298.15 K for the reactions
involving iodine and CS 2 . They first measured the enthalpy of formation of SnI 4 from
elements in solution according to the reaction:
ο
f 1
β-Sn + 2 I 2 (cr) +CS 2 (l) SnI 4 (CS 2 solution) ( Δ H = − (195.39 ± 1.2) kJ·mol –1 )
and then
ο
f 2
SnI 4 (cr) + CS 2 (l) SnI 4 (CS 2 solution) ( Δ H = (13.39 ± 0.42) kJ·mol –1 )
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012