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

A Discussion of selected references
331
[1971PET2]
The interaction of molybdate with pyrophosphate ion have been studied by
potentiometry. The author reported reliable dissociation constants of phosphoric acid in
3 M NaClO 4 .
[1972DES/JOV]
Equilibrium potentials of the redox couple Sn(IV)/Sn(II) on Hg were measured as
functions of concentrations of Sn 2+ , Sn 4+ , Cl – , and H + in aqueous solutions containing
4 M HCl and 1 M Na 2 SO 4 + 1 M H 2 SO 4 , respectively. To identify the Sn(IV) species
present in these solutions and to determine their stabilities, a method of analysis of
potentiometric data was developed, based on the comparison of the Sn(IV) complexes
with those of Sn(II) determined at I = 0 by [1949RIC/POP]. The derived stability
constants have been tabulated, and the calculated distribution of the Sn(IV) complexes
as a function of the Cl – concentration has been presented.
In order to re-evaluate the results of [1972DES/JOV] Figures 2, 3 and 5 of this
paper have been digitalised.
From Figure 2 equilibrium potentials of Reaction (A.47)
Sn 4+ + H 2 (g, r) Sn 2+ + 2 H + (aq, r)
(A.47)
in solutions (I) and (II) were obtained. In Eq. (A.47) “r” is used to indicate that H 2 (g)
and H + (aq) are at the chemical conditions in the reference electrode compartment, see
Eq. (B.14).
I: [Sn(IV)] = 1.0 × 10 –1 M, [HCl] = 4.0 M, [Sn(II)] = 0.003 to 1.0 M.
II: [Sn(IV)] = 1.0 M, [HCl] = 4.0 M, [Sn(II)] = 0.0003 to 1.0 M.
Figure 3 provides equilibrium potentials of Reaction (A.47) in solutions (III)
and (IV).
III: [Sn(II)] = 1.0 × 10 –1 M, [HCl] = 4.0 M, [Sn(IV)] = 0.001 to 1.0 M.
IV: [Sn(II)] = 1.0·M, [HCl] = 4.0 M, [Sn(IV)] = 0.001 to 1.0 M.
Figure 5 contains equilibrium potentials of Reaction (A.47) in solutions (V). V:
[Na 2 SO 4 ] = 1.0 M, [H 2 SO 4 ] = 1.0 M, [Sn(IV)] = [Sn(II)] =0.01 M, [Cl – ] = 0.06 to 3.0 M.
The equilibrium potentials of Reaction (A.47) in solutions (V) can be
represented by Eq. (A.48).
ο
E = E
V
(Sn 4+ /Sn 2+ ) − (RT/2F)·ln(10)·log 10 {[Sn 2+ ]/[Sn 4+ ]}
(A.48)
According to Despić et al. the total concentrations of di- and tetravalent tin can
be expressed by
[Sn(II)] = [Sn 2+ ] + [SnCl + ] + [SnCl 2 ] + [ SnCl − 3
] + [ SnCl − ]
2
4
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012