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

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A Discussion of selected references
solubility data up to [I – ] ini = 1.0 M, therefore further studies are required to establish the
composition and stability of the formed complexes at higher iodide concentrations.
[1968HAL/SLA]
The formation constants for the fluoride complexes of Sn(II) were determined by
potentiometric measurements by using both tin amalgam and fluoride ion selective
electrodes under nitrogen atmosphere. The experiments were performed using constant
tin(II) concentration at ionic strength of 0.85 M and at three different temperatures
(t = 25, 45 and 60 °C). The background electrolyte used in this study is ambiguous.
Although, no information is provided about the inert electrolyte (0.85 M) used for the
measurements, the calibration of the fluoride selective electrode was made in 0.1 and
1.0 M perchlorate media, thus 0.85 M NaClO 4 was presumably the background
electrolyte. Some further experimental details (concentration of [Sn 2+ ] tot and [H + ] tot in
the solutions) were not reported in [1968HAL/SLA], too. Taking into account the fact
that ([F – ] tot – [F – ] free )/3 should be nearly equal with [Sn 2+ ] tot at the end of the titrations,
[Sn 2+ ] tot ≈ 0.015 M can be estimated. Using such a high [Sn 2+ ] tot concentration pH ≤ 2
have to be used to prevent the hydrolysis of tin(II), but below pH ≈ 3 the protonation of
fluoride ion should be taken into account, and this is not the case in [1968HAL/SLA].
Nevertheless, the experimental data given in [1968HAL/SLA] were re-evaluated for the
purposes of this review. The following formation constants were obtained: log10 β 1 =
(4.60 ± 0.24) (3σ), log10 β 2 = (8.01 ± 0.24), log10 β 3 = (10.38 ± 0.18) at t = 25 °C;
log10 β 1 = (4.62 ± 0.15) (3σ), log10 β 2 = (7.92 ± 0.21), log10 β 3 = (10.40 ± 0.15) at
t = 45 °C and log10 β 1 = (4.72 ± 0.12) (3σ), log10 β 2 = (8.73 ± 0.09), log10 β 3 =
(10.47 ± 0.24) at t = 60 °C. Considering the missing experimental details, the
reported/recalculated formation constants were not considered any further in this
review.
[1968HOW/MOS]
Single crystals of tin(II) hydroxide oxide have been obtained. The crystals of tin(II)
hydroxide oxide possess tetragonal symmetry. The space group is determined uniquely
as P 4 /mnc. The unit cell dimensions (a = (7.93 ± 0.01), c = (9.13 ± 0.01) Å) refined by
comparison with published diffraction data [1961DON/MOS], and the density of the
material are compatible only with the presence of four formula units of 3SnO·H 2 O per
unit cell.
Donaldson and Moser [1961DON/MOS] have shown that there is only one
stable solid tin(II) hydroxide, a unique crystalline phase quite distinct from other tin(II)
oxides, which can be described as hydrous oxide or better tin(II) hydroxide oxide. The
formula of the finely divided material was determined analytically as 5SnO·2H 2 O.
Table A-22 shows that analytical results may not be able to distinguish between these
and the alternative formula Sn 3 O(OH) 2 of Howie and Moser [1968HOW/MOS].
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012