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

A Discussion of selected references
291
later re-evaluated by Rabideau and Moore [1961RAB/MOO] who rejected the
formation of hydroxido complexes [1961RAB/MOO]. Moreover, Tobias and Hugus
[1961TOB/HUG] demonstrated experimentally, that in the solutions with [H + ] tot = 0.05
to 0.5 M no hydrolysis of tin(II) should be considered [1961TOB/HUG].
The constants of the reactions
Sn 2+ + H 2 O(l) SnOH + + H +
SnOH + + Cl – Sn(OH)Cl
were evaluated from the variation of the cell data with acidity, and were recalculated on
the basis of the data given in Table 2 [1952VAN/RHO], the results could be reproduced
only approximately. As the total Sn 2+ concentration was not varied polynuclear complex
formation cannot be excluded. The experimental data were explained with 5 complex
formation constants, i.e. for SnOH + , Sn(OH)Cl, SnCl + , SnCl 2 , SnCl − 3 . The values for
the formation constants of SnOH + and Sn(OH)Cl can only be regarded as tentative.
Therefore, the experimental data reported in [1952VAN/RHO] were reevaluated
for the purposes of this review assuming that the differences between the
measurements performed at different [H + ] tot concentrations are due to some unknown
experimental errors. Due to the replacement of NaClO 4 by both HClO 4 and NaCl, up to
37% of the background electrolyte was substituted during the measurements. Although
no apparent medium effect was observed by [1961TOB/HUG] under similar conditions,
considering the above mentioned unknown experimental errors an uncertainty of ± 0.3
has been assigned to the recalculated log10
β
q
values (see Table VIII-9).
The temperature dependence of the formation constants allowed us to calculate
2−q
the reaction enthalpy for the formation of SnCl (q = 1, 2, 3) complexes:
q
Sn 2+ + q Cl – 2 q
SnCl
− . (A.27)
q
From the plot in Figure A-16, Δ
rH
m((A.27), q = 1) = (9.8 ± 1.0) kJ·mol –1 ,
Δ
rHm((A.27), q = 2) = (14.1 ± 2.0) kJ·mol –1 and Δ
rHm((A.27), q = 3) =
(17.2 ± 4.0) kJ·mol –1 can be derived.
[1953HUM/OBR]
The enthalpies of formation of tin(II) oxide and tin(IV) oxide at 298.16 K were
determined by combustion calorimetry of Reactions (A.28) and (A.29) at 303.16 K.
β-Sn + O 2 (g) SnO 2 (cr)
SnO(cr) + 0.5 O 2 (g) SnO 2 (cr)
(A.28)
(A.29)
The authors were careful in synthesising the SnO sample, and their final
sample was heated in hydrogen at 220 to 256 °C for 4 hours. The product after this
treatment gave w SnO = 99.5%, w HO 2 = 0.18% and w CO2
= 0.10%, leaving 0.15%
undetermined. There was evidence of the presence of Sn(IV) oxide which probably
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012