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

A Discussion of selected references
287
measurements no appreciable amount of SnCl −
3
can be detected in the solution, and the
value of log10 β
2
is also strongly affected. Considering the above facts, only log10 β
1
=
(1.07 ± 0.4) will be considered further in this review.
[1951DUK/PIN]
The reaction rate between Fe(III) and Sn(II) has been studied as a function of the halide
ion (Cl – , Br – , I – ) concentrations at 25 °C in 2.03 M HClO 4 medium. The authors
concluded that a minimum of three halide ions (bound to the reacting Fe(III) and Sn(II)
ions in total) are required to be added to the activated complex for any appreciable
reaction rate, and more halides considerably enhance the possibility of the reaction. The
order of increasing effectiveness is Cl – < Br – < I – , which is probably due to the
increasing ease of oxidation of the halide ions.
The formation constants of the complexes SnCl + and SnBr + derived in this
work can be only regarded as a rough approximation, therefore an uncertainty of ± 0.5
has been assigned to the reported log10 β 1 values.
[1951POW/LAT]
The standard partial molar entropies of monatomic ions and of non-electrolytes in
aqueous solutions can be represented by empirical expressions, for monatomic ions the
following equation has been found to be valid:
ο
S
m
/cal·mol –1·K –1 = 1.5·(R/cal·mol –1·K –1 )·ln (M /g·mol –1 ) + 37 – 270·z·(Å/r e ) 2
where z is the absolute value of the charge on the ion, M the molar mass and r e the
effective radius of the ion. For cations r e /Å = 2.0 + r x /Å, r x being the crystal radius.
In Table A-8 partial molar entropies of monoatomic ions, its uncertainties and
the respective references as well as the effective ionic radii, r x (‘IR’), given by Shannon
[1976SHA] are listed. The Powell-Latimer equation has been fitted to these data,
weighted by uncertainties of entropies. The uncertainties of S ο m (Cr 3+ ) and S ο m (Th 4+ )
have been estimated according to the discussion in [1976DEL/HAL] and set equal to the
ο
m
uncertainty of S (Zr 4+ ) [2005BRO/CUR], respectively. Slightly modified coefficients
were obtained for the Powell-Latimer equation.
ο
S
m
/J·K –1·mol –1 = 1.5·(R/J·K –1·mol –1 )·ln (M /g·mol –1 ) + (156.84 ± 0.26)
– (1237.62 ± 2.14)·z·(Å/r e ) 2
It should be emphasised that aqua americium(III) and aqua uranium(IV) ion
appear twice in this correlation, with the conventional coordination number n = 6 and
those coordination numbers assigned to them by [1992SAS/SHO], namely n = 8 and
n = 9, respectively.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012