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

VII.2 Solid tin oxides and hydroxides 121
similar result (47.756 J·K –1·mol –1 ο
) by linear regression of C p,m
between 263 and 311 K,
see Appendix A on [1978KOS/SAM].
From T ≈ 250 K upwards the heat capacities of SnO(cr) measured by
[1929MIL2] deviate increasingly from those of [1978KOS/SAM] and thus were not
considered in this review.
ο
( Cp,m
The entropy may be calculated by integrating /T) with respect to T
ο
where C
p,m
is given by Eq. (VII.15), but the coefficients of Eq. (VII.15) were slightly
ο
modified by non linear regression of data T, C / p,m
T , see Appendix A entry on
[1978KOS/SAM].
ο
m
ο
C p,m
S (SnO, cr, 298.15 K) = (4.281 K)/3 +
298.15K
∫ 4.281K
ο
p,m
( C / T)dT
= (57.180 ± 0.220) J·K –1·mol –1 .
–1
This value of the entropy overlaps with the value of (57.17 ± 0.08) J·K
–1·mol
given by [1978KOS/SAM] and the CODATA key value (57.17 ± 0.30) J·K –1·mol –1 )
[1989COX/WAG].
VII.2.2.3
Solubility of SnO(cr)
The determination of the solubility constant of SnO(cr) in aqueous solutions, such as
defined by Eq. (VII.16), is in principle a straightforward method and can be used to
ο
evaluate the standard Gibbs energy of formation, Δ fGm(SnO, cr, 298.15 K), of the solid
SnO phase.
SnO(cr) + 2 H + Sn 2+ + H 2 O(l)
Δ
Δ
ο
solGm
ο
fGm
(VII.16)
(VII.16) = − RT· log K (VII.17)
ο
m
* ο
10 s0
(SnO, cr) = Δ G (Sn 2+ ) + Δ G (H 2 O, l) −
f
f
ο
m
Δ s ln
G (VII.16)
ο
m
(VII.18)
In the case of solubility studies on SnO(cr) complications arise, because Sn 2+
forms hydroxido complexes such as SnOH + 2
and Sn3(O H) +
4 at comparatively low pH
values as well as chlorido complexes at rather low chloride concentrations. Thus
reactions described by Eqs. (VII.19) to (VII.21) will contribute to the dissolution
process even in the acidic range.
SnO(cr) + H + SnOH +
3 SnO(cr) + 2 H + 2
+ H 2 O(l) Sn 3(OH) +
4
SnO(cr) + 2 H + + Cl – SnCl + + H 2 O(l)
(VII.19)
(VII.20)
(VII.21)
There are only three solubility studies which report data useful for the
ο
evaluation of Δ G (SnO, cr): [1941GAR/HEI], [1942GOR/LEI] and [1966MES/IRA].
f
m
Garrett and Heiks [1941GAR/HEI] equilibrated SnO(s) in dilute HCl solutions.
An attempt was made to approach equilibrium from supersaturation and
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012