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

A Discussion of selected references
359
calculations in acid solutions. The mean values thus obtained (molarity basis, I = 3.0 M
(Na)ClO 4 , 25 °C) were:
SnO(s) + H 2 O(l) Sn 2+ + 2 OH –
log10 K s,0 (A.69) = − 25.43 (SnO(s) dissolved in hydroxide)
log10 K s,0 (A.69) = − 25.4 (SnO(s) dissolved in acid).
(A.69)
The value for SnO(s) dissolved in hydroxide has been obtained by combining
Mark’s (I = 3.0 M (Na)ClO 4 ) and Garret and Heiks’ (I = 0) results for 25 °C
[1941GAR/HEI]:
Sn 2+ + 3 OH – Sn(OH) − 3
log10 β 3 = 24.58
SnO(s) + H 2 O(l) + OH – Sn(OH) −
3
log ο
10 K 1,1 = − 0.85.
As Garret and Heiks’ dissolution reaction is isoelectronic, the ionic strength correction
is probably small and can be neglected indeed.
The value designated by SnO(s) dissolved in acid, has been recalculated using
the re-evaluation of [1941GAR/HEI] by this review:
* ο
log10 K s,0 (m) =
* ο
log10 K s,0 (M) =
SnO(s) + 2 H + Sn 2+ + H 2 O(l)
*
10 s,0
log K (m) – 2D + log10 a H2O
+ {ε(Sn 2+ , ClO − 4 )
– 2ε(H + , ClO − 4 )}·m( ClO − 4 )
*
log10 K s,0 (m) + log10
ξ
*
log10 K s,0 (M) = 2.00 + 0.5004 + 0.0535 + 0.3163 + 0.0674 = 2.94.
Combining this value with the ionic product of water at I = 3.0 M (Na)ClO 4 ),
log10 K w = − 14.22 [1957ING/LAG] results in log10 K s,0 = − 25.50 in reasonable
agreement with Mark’s estimation.
[1977SMI/KRA]
The potential of a tin-amalgam electrode as a function of tin(II) and hydroxide ion
concentration has been determined at 298 K in 3 M NaClO 4 medium. Since between
[OH – ] = 0.02 and 1 M only the species Sn(OH) −
3 exists in the solution, the electrode
reaction can be defined as Sn(OH) − 3 + 2 e – Sn(s) + 3 OH – ο
. E ( Sn(OH) − 3 /Sn) =
0.87 V was determined as the standard potential of this reaction. Using the literature
ο
data E (Sn 2+ /Sn(0)) = − 0.136 V, the authors calculated the formation constants of
Sn(OH) − 3 (Sn 2+ + 3 OH – Sn(OH) − 3 , log10 β 3 = 24.8). The authors observed some
deviation from the linearity of the E ( Sn(OH) − 3 /Sn) vs. [OH – ] curve below [OH – ] =
0.02 M. This was explained by the dissociation of the complex Sn(OH) − 3 . A value of
pK d = (1.95 ± 0.05) was reported for the reaction Sn(OH) − 3 Sn(OH) 2 (aq) + OH – .
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012