CHAPTER 11 • Hydrolysis Processes of Organotin(lV) Compounds in Sea Water
223
linities is reported in Table 11.6 (De Stefano et al. 1994 and refs. therein). Therefore, besides the hydrolysis processes of organotin cations, interactions with seawater anions
(chloride and sulfate) must also be considered, after all the internal interactions of background salt components have been taken into account (De Robertis et al. 1994). In order
to simplify equilibrium calculations, and to give a cumulative picture of the complexing
capacity of seawater toward this class of compounds, the composition of SSWE can be
expressed in terms of a single salt, BA, whose ions have a charge z = ±1.117 (De Stefano
et al. 1998a). Concentrations of BA (mean ionic concentration) at different salinities are
reported in Table 11.6, too. The anion (A) of this salt forms the species BAo, HA(z-l).
The chemical speciation model for artificial seawater (expressed both as six components and as a single salt, BA) and the equilibrium constants and thermodynamic
parameters for the system BA are reported in Table 11.7.
By using the single salt approximation (BA), a chemical model where, as well as
hydrolysis processes, the binary and ternary interactions of each [RxSn(4_x)lz+ cation
with A z- and BZ+ and the internal association of BA have also been taken into account,
has been built up according to the scheme in Table 11.8.
Table 11.6. Composition of SSWE at 35%0 and T = 25 DC (concentrations in mol dm -3, at 25 DC)
Component
5(%0)
S
1S
2S
3S
NaCI
0.0590
0.1782
0.2992
004221
Na 2 S0 4
0.0040
0.0122
0.0204
0.0288
KCI
0.0015
0.0046
0.0078
0.01 1
CaCI 2
0.0015
0.0047
0.0078
0.01 "
MgCl 2
0.0077
0.0231
0.0389
0.0548
BA
0.0803
0.2428
004078
0.5751
0.1000
0.3030
0.5090
0.717
Table 11.7. Speciation model for SSWE
Equilibrium
logK a
H+
Na+
K+
Mg2+
M + Hp= M(OH) + H+
-14.0
-14.3
-11.7
M+Ci=MCI
-0.6
-0.5
0.1
M+50 4 =MS0 4
1.70
0.5
0.6
1.6
a Formation constants at 'eff = 0.56 mol dm -3 (35%0 salinity) and T = 25 'c.
b S1.117+ + A1.117-=ASo.
( H+ +A1.117-=HAo. 117 -.
4S
0.5467
0.0373
0.0142
0.0143
0.0710
0.7449
0.929
Ca 2 +
81.117+
-12.9
-12.9
0.0
(-0.39)b
1.5
(-0.04)(
223
linities is reported in Table 11.6 (De Stefano et al. 1994 and refs. therein). Therefore, besides the hydrolysis processes of organotin cations, interactions with seawater anions
(chloride and sulfate) must also be considered, after all the internal interactions of background salt components have been taken into account (De Robertis et al. 1994). In order
to simplify equilibrium calculations, and to give a cumulative picture of the complexing
capacity of seawater toward this class of compounds, the composition of SSWE can be
expressed in terms of a single salt, BA, whose ions have a charge z = ±1.117 (De Stefano
et al. 1998a). Concentrations of BA (mean ionic concentration) at different salinities are
reported in Table 11.6, too. The anion (A) of this salt forms the species BAo, HA(z-l).
The chemical speciation model for artificial seawater (expressed both as six components and as a single salt, BA) and the equilibrium constants and thermodynamic
parameters for the system BA are reported in Table 11.7.
By using the single salt approximation (BA), a chemical model where, as well as
hydrolysis processes, the binary and ternary interactions of each [RxSn(4_x)lz+ cation
with A z- and BZ+ and the internal association of BA have also been taken into account,
has been built up according to the scheme in Table 11.8.
Table 11.6. Composition of SSWE at 35%0 and T = 25 DC (concentrations in mol dm -3, at 25 DC)
Component
5(%0)
S
1S
2S
3S
NaCI
0.0590
0.1782
0.2992
004221
Na 2 S0 4
0.0040
0.0122
0.0204
0.0288
KCI
0.0015
0.0046
0.0078
0.01 1
CaCI 2
0.0015
0.0047
0.0078
0.01 "
MgCl 2
0.0077
0.0231
0.0389
0.0548
BA
0.0803
0.2428
004078
0.5751
0.1000
0.3030
0.5090
0.717
Table 11.7. Speciation model for SSWE
Equilibrium
logK a
H+
Na+
K+
Mg2+
M + Hp= M(OH) + H+
-14.0
-14.3
-11.7
M+Ci=MCI
-0.6
-0.5
0.1
M+50 4 =MS0 4
1.70
0.5
0.6
1.6
a Formation constants at 'eff = 0.56 mol dm -3 (35%0 salinity) and T = 25 'c.
b S1.117+ + A1.117-=ASo.
( H+ +A1.117-=HAo. 117 -.
4S
0.5467
0.0373
0.0142
0.0143
0.0710
0.7449
0.929
Ca 2 +
81.117+
-12.9
-12.9
0.0
(-0.39)b
1.5
(-0.04)(