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

A Discussion of selected references
433
The values of ε 1 = 0.0865 (0.10559) kg mol –1 and ε 1.5 = 0.0290 (0.00932)
kg 1.5·mol –1.5 were obtained from log 10 γ ± data at 0.1 ≤ m −
ClO /mol kg –1 ≤ 8.0
4
[1965HAA/DUC] and 0.001 ≤ m HCl /mol kg –1 ≤ 8.0 [1972HAM/WU], the ε values of
HCl are in parenthesis.
(ii) Let us assume that the analysis of log10 γ +
H vs. m −
ClO results in
4
see Table B-6.
log γH =− D+ ε (H ,ClO ) m + ε (H ,ClO ) m log [ m ] (A.97)
+ − + −
10 + 1 4 −
ClO4 lg 4 −
ClO4 10
−
ClO4
For the sake of brevity ε 1 (H + , ClO4
− ) = ε 1 and ε lg (H + , ClO4
− ) = ε lg .
The modified SIT approach leads to Eqs. (A.98) and (A.99) for evaluation of
Δε:
o
E and
ο k
o k
E ' + { 10D+ 2εlgm −
ClO log }
4 10[ m −
ClO ] = E + Δ εm
−
4 ClO4
2 2
(A.98)
k ⎧⎪
⎡
4
Sn
o
log + ⎤
⎫⎪
k
E− ⎨ 10 10D 2ε
2
lgm −
ClO log
4 10[ m −
ClO ] E εm
−
⎢ ⎥− −
4 ⎬= + Δ ClO4
2⎪
m 2+ Sn
m +
⎩ ⎣ H ⎦
⎪⎭
2
(A.99)
The values of ε 1 = 0.1079 (0.1121) kg mol –1 and ε lg = 0.06506 (0.02126)
kg mol –1 were obtained from log 10 γ ± data at 0.1 ≤ m −
ClO /mol kg –1 ≤ 8.0
4
[1965HAA/DUC] and 0.001 ≤ m HCl /mol kg –1 ≤ 8.0 [1972HAM/WU], the ε values of
HCl are in parenthesis.
As pointed out in the beginning the measurements were carried out using a
mixture of HCl and HClO 4 as background electrolyte. Patwardhan and Kumar
[1986PAT/KUM] showed that the reduced overall activity coefficient of a mixed
electrolyte solution Γ * is related to the reduced activity coefficients Γ i,r of the single
electrolyte solutions, z i is the charge on single ionic species:
( )
log10 Γ
r
= log
10
γ ±
/ zz + −
m
For 1:1 electrolytes Γ
r
= γ ±
and i
is the ionic strength fraction, thus
I
*
log Γ = ∑ log Γi
(A.100)
10 r 10 ,r
i
where the individual ionic activity coefficients Γ = γ ±
have to be taken at m i = I.
With Eq. (A.100) the modified formulae used for extrapolation read as
Eqs (A.96) and (A.99), but ε 1.5 and ε lg were replaced by
ε mHClO
m
4
HCl
1.5,tot
=
1.5
(HClO
4
)
1.5(HCl)
I
ε +
I
ε
HClO4
HCl
and ε m
m
lg,tot
=
lg
(HClO
4
)
lg
(HCl)
I
ε +
I
ε , respectively,
and m
HClO 4
was replaced by I m .
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012