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

A Discussion of selected references
381
ο
E (Sn 4+ /Sn 2+ , 6.0 M HCl, 298.15 K) = 99.0 mV
ο
vs. the standard hydrogen electrode (SHE), as E
h
(SCE) = 244.4 mV [1961IVE/JAN].
The authors state in this context that 130 mV (NHE) = − 138 mV (SCE), which would
be correct for the standard calomel electrode, leading to
ο
E (Sn 4+ /Sn 2+ , 6.0 M HCl, 298.15 K) = 122.6 mV.
Unfortunately the authors fail to clearly identify their reference electrode,
consequently it cannot be decided which value is the correct one.
Probably the following cell was used
Hg | SnCl 4 , SnCl 2 , HCl KCl (sat.) KCl (sat.) | Hg 2 Cl 2 | Hg.
Regardless of the meagre experimental details the advantage of these
measurements is that in 6 M = 6.8508 mol·kg –1 HCl Sn(IV) hydrolysis can no longer
play an important role. Thus provided a series of such cell-potential data in, say, 4, 5, 6,
ο
7 molal HCl would exist E (Sn 4+ /Sn 2+ , 298.15 K) could probably be derived without
taking Sn(IV) hydrolysis into consideration.
[1981IZU]
The Rietveld profile-analysis refinement procedure has been applied to X-ray powder
diffractometer data collected from tin(II) oxide with CuKα radiation. Four symmetric
profile functions were tested; the use of a modified or an intermediate Lorentz function
led to a more satisfactory fit than the use of the Gauss or Lorentz function. The
positional parameter of the tin atom was found to be 0.2369, which is almost identical
with the corresponding value reported for isomorphous lead(II) oxide.
With the unit cell parameters, a 0 /Å = 3.7986(1), c 0 /Å = 4.8408(2), Z = 2, the
density of SnO(tetr.) is calculated to be ρ = (6409 ± 1) kg·m –3 .
[1981LAV/TIM]
Lavut et al. used combustion calorimetry to measure the enthalpy of reaction of tin (IV)
and tin (II) oxides yielding the energies of the reactions:
Sn(tetragonal) + O 2 (g) SnO 2 (tetragonal)
SnO(tetragona1) + 0.5 O 2 (g) SnO 2 (tetragonal)
and the enthalpies of formation of SnO 2 (cr), and SnO(cr) were calculated.
They emphasise that particular attention was given to the analytical
characteristics of the starting samples. They employed two different samples and
characterised the sample to a purity of 99.99% or better. They also used X-ray
diffraction and showed the crystals to belong to the tetragonal system. They carefully
timed the experiments to attain equilibrium for two hours prior to commencement of the
measurement. The duration of the main period was 1 hour. Relevant checks showed that
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012