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

A Discussion of selected references
315
Figure A-25: Temperature dependence of ε(H + , ClO − 4 ) (: data from linear regressions;
solid line: ∂ε / ∂ T = 0, ε(H+, ClO − 4 ) = 0.147 kg·mol –1 ; dashed line: linear fit ∂ε
/ ∂ T =
− (0.97 ± 4.7) × 10 –4 kg·mol –1·K –1 ; dotted lines: 95% confidence limits).
0.156
0.154
0.152
ε(H + ,ClO 4
–
)/kg·mol
–1
0.150
0.148
0.146
0.144
0.142
0.140
280 285 290 295 300 305 310 315
T / K
[1966MES/IRA]
The stability of tin(II)-pyrophosphate and -tripolyphosphate complexes has been
determined by equilibrating the polyphosphate solutions with solid SnO. The
measurements were performed between pH 5 to 7, at 25 °C and in 1 M NaClO 4 solution
under nitrogen atmosphere. High purity SnO (Baker and Adamson) was used, but
further characterisation is not provided. The dissolved tin(II) was determined
iodometrically. The equilibration of the two phases lasted 24 hours. Sodium complexes
of pyrophosphate were not taken into account in the calculations. The solubility of SnO
showed a maximum around pH 5. The pyrophosphate proved to be a strong complex
forming ligand, since the concentration of the dissolved tin(II) exceeded the
4
concentration of pyrophosphate in solution with [ PO − 2 7
] T = 0.005 or 0.015 M, therefore
the authors suggested the formation of polynuclear complexes. The whole set of data
was explained by the following three reactions and equilibrium constants
2 SnO + H + + HPO x
2 SnO + H + +
2 SnO + HPO x
−4
x 2 4
4
2H P2O x −
x 4
−4
x 2 4
complex 1 (K 1 = 6 × 10 5 )
complex 2 (K 2 = 2 × 10 8 )
complex 3 . (K 3 = 0.3)
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012