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

A Discussion of selected references
285
No solubility experiments in pure water were tried due to hydrolysis, but it was
attempted to fix the eutectic temperature (t = − 6.8 °C and 37.9% SnCl 2 ). Points on the
ice curve are given at (− 6.25 °C, 36.8%) and (− 6.45 °C, 37.3% SnCl 2 ).
Approximate solubility data are plotted for 0 °C from measurements in a
company lab.
Temperature variation given as ± 0.05 K. Evidence for equilibrium is given,
but no explicit information that oxidation of tin(II) was avoided in starting material and
during experiments.
[1947SAP/KOH]
SnO in the solid state is unstable, disproportionation according to 4 SnO → Sn 3 O 4 + Sn
is observed between 400 and 1040 °C. Molten SnO, however, is stable. Melts of the
composition SnO are obtained if cold pellets of SnO or SnC 2 O 4 are introduced into
Al 2 O 3 crucibles heated to approximately 1200 °C. Melts of similar appearance are
obtained if mixtures of Sn and SnO 2 (1:1) or SnO 2 and C (1:1) are treated similarly.
SnO forms a yellow Sn(II) silicate glass with SiO 2 at 1000 °C. Neither Sn nor SnO 2
reacts similarly with SiO 2 . The SnO melts solidify at 1040 °C; this is also the
temperature at which the disproportionation begins on cooling. In comparison with Sn
and SnO 2 , SnO is very volatile; the boiling point is estimated to be approximately
1700 °C. The thermal properties of SnO are compared with those of CO, SiO, and GeO.
[1949RIC/POP]
Composition and stabilities of Sn(II)-chlorido complexes were investigated
polarographically in KCl solutions.
From the half-wave potential of the reaction Sn 2+ + 2 e – Sn(0) vs. the
normal calomel electrode according to Reaction (A.24)
Sn 2+ + 2 Cl – + (sat)Hg(l) Sn(Hg) sat + Hg 2 Cl 2 (s)
and the standard potential of Reaction (A.25)
(A.24)
2 H + + 2 Cl – + 2 Hg(l) H 2 (g) + Hg 2 Cl 2 (s) (A.25)
and accounting for a Sn in a saturated tin amalgam [2003YEN/GRO], the half-cell
potential for Sn 2+ + 2 e – Sn(cr) was determined in 1 M KCl solutions. For Reaction
ο
ο
(A.24), E (1 M KCl, 298.15 K) = − 433 mV and for Reaction (A.25) E (1 M KCl,
298.15 K) = − 278 mV are reported. This leads to a half-cell potential for Sn 2+ + 2 e –
Sn(cr) of E
co ' (I = 1.0 M KCl, 25 °C) = − (154.03 ± 2.00) mV. The uncertainty of
± 2 mV has been estimated by this review. With a value for ε(Sn 2+ , Cl – ) = (0.14 ± 0.10)
kg·mol –1 , Eq. (II.35), and Eq. (VI.5) lead to:
o 2+ o ⎛RT
ln(10) ⎞ ⎡ ⎛mKCl
⎞
⎤
Em(Sn /Sn) = Ec ' + νi
log10 2D ε m −
⎜ ⎟⋅⎢∑
⋅ + +Δ ⋅
Cl ⎥
nF
⎜
c
⎟
⎝ ⎠ ⎣ ⎝ KCl ⎠
⎦
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012