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

284
A Discussion of selected references
As the perchlorate ion is not capable of forming complexes with Sn 2+ this study
is potentially very interesting.
The solubility determining species in the acid range investigated is Sn 2+ ,
whereas SnOH + 2
and Sn 3(OH) +
4 are responsible for only 5 to 10% of dissolved Sn(II).
When three reactions participate in a dissolution process it is far more reliable to base
the stability constant determination on experiments in homogeneous solution, e.g.
[1958TOB], [1976GOB].
Consequently the re-evaluation of Gorman and Leighton’s data was based on
the stability constants selected by this Review. For comparison with [1941GAR/HEI]
the data were transformed to the molality basis. The re-evaluation (see Figure VII-9) led
to the same result as [1941GAR/HEI]:
f
ο
m
which is equivalent to
Δ G (SnO, cr, 298.15 K) = − (253.29 ± 1.38) kJ·mol –1
log
*
10 s,0
K (SnO, cr, 298.15 K) = (2.05 ± 0.24)
for Reaction (A.23), when the selected Δ fGm(Sn 2+ , 298.15 K) = − (27.39 ± 0.30)
kJ·mol –1 ο
and Δ fGm(H 2 O, l, 298.15 K) = − (237.14 ± 0.04) kJ·mol –1 from the NEA
auxiliary data are taken into account.
SnO(cr) + 2 H + Sn 2+ + H 2 O(l).
ο
(A.23)
This work suffers from two methodological deficiencies. (1) The pH values of
the equilibrated solutions were not measured. Thus information on the concentration of
free H + can be obtained from the analytical charge balance only, but this depends on all
reactions participating in the dissolution process. As the evaluation has to be based on
the initial molality of HClO 4 and the equilibrium molality of Sn(II), it is necessarily less
precise. (2) The solid tin(II) oxide studied has not been characterised by taking its X-ray
powder diffraction pattern, thus the identity of the actually investigated phase has not
been unambiguously ascertained.
[1947RYS/TUR]
Solubility determinations in the system HCl-SnCl 2 -H 2 O at 5, 15 and 25 °C had been
performed at concentrations of HCl from 2 to 10%. Results are tabulated. Also results
from [1888ENG] at 0 °C are listed and discussed as not in agreement with this work.
Solubility experiments were performed in a thermostat rotating the closed tubes
“over-head” for 3 hours. Previous experiments from sub- and supersaturation confirmed
equilibrium after 2-3 h. After density determination the liquid samples were titrated for
Sn 2+ (iodometrically) and for total acid with NaOH against phenolphthalein in boiling
solutions. Solid phase composition was determined by Schreinemakers method yielding
the dihydrate in all cases.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012