TATB assumption

It is interesting that the experimentally measured zero-charge potential is practically identical with the value of A = 0, calculated using the TATB assumption (3.2.64). This fact helps to justify the use of this assumption. 

The following data are for the Gibbs energy of transfer from water to propylene carbonate for 1-1 electrolytes at 25°C [37]. Use these data to estimate the corresponding quantities for the individual ions on the basis of the TATB assumption. 

Several extrathermodynamic assumptions have been considered to separate experimental values of Atr//° into cationic and anionic contributions [35]. The one commonly used is the TATB assumption, namely, that the contributions to... 

Ion solvation in polar solvents is also an important aspect of the subject matter considered here. This is traditionally studied by measuring the Gibbs energy and enthalpy of transfer of a variety of electrolytes from water to another polar solvent. Single ion quantities are then derived on the basis of the TATB assumption. Study of these quantities for simple monoatomic ions like the alkali metal cations and the halide anions leads to the conclusion that specific molecular properties, namely, Lewis acidity and basicity, are important in ion solvation. On the other hand, the dielectric permittivity, a non-specific bulk property. 

Because the partition equilibria observed at the liquid liquid interface are relevant to interfacial phenomena in specific ion electrodes and biological membranes, there is an interest in determining single ion quantities associated with transfer of an ion from water to the non-aqueous phase. This quantity can only be estimated from experimental data after making an extrathermodynamic assumption. One common assumption discussed earlier in section 4.8 is the so-called TATB assumption, according to which... 

Table 8.11 Standard Gibbs Energy of Transfer for Monovalent Ions from Water to Nitrobenzene at 25°C (TATB Assumption) [18]...

This fundamental parameter quantifies the relative affinity of an ion in the two phases, but it is not directly accessible experimentally because it is associated with a single ionic component. Therefore, to make AGf 1 0 or logP1,0 amenable to direct measurement, an extrathermodynamic assumption must be introduced such as the Grunwald or TATB assumption [139], which states that the cation and the anion of tetraphenylarso-nium tetraphenylborate (TPAs+TPB or TATB) have equal standard Gibbs energies for any pair of solvents [140,141] ... 

Observed standard molar Gibbs transfer energies 4G , at 25°C for Cs ion, based on the TATB assumption (see Table 4). 

The TATB assumption was used for the experimental values of ACt,- Gibbs energy changes are expressed in kj/mol on the molarity scale. 

Original data were obtained as sodium salt partition constants (log/C,. ) but had been reported as the individual anion partition constants via the relation logATi(A ) = ogKi - log/CdNa" ), where log/Cj(Na ) = -6.0 (TATB assumption). 

Upon making an extrathermodynamic assumption such as the TATB assumption, the standard Gibbs energy of the salt partitioning process given by Eq. (33) becomes simply... 

All data were obtained at 25°C unless noted otherwise. The TATB assumption applies in all cases. 

An extra thermod3mamic assumption is required in order to describe the transfer properties of individual ions, and consistent values, obeying AtGi°° = Hi°° — TAiSi°°, are obtained when the transfer quantities of Pli As and BPh4 are assumed to be equal (the TATB assumption) as is widely employed [6]. The results for transfer of ions into many pure organic solvents have been summarized by Marcus [1] and those for transfer into mixed aqueous-organic solvents by him with coworkers [7]. 

On the whole, conceptually the reference electrolyte extra-thermodynamic assumption for A G ° is sound, and its implementation by means of the TATB assumption has been deemed to be reliable by a number of authors, [23, 24, 29, 30] among others, as the least objectionable one. The validity of other assumptions might be and has been tested against the TATB assumption, although there is no certainty in its own validity. An estimate of its possible reliability is 2kJ-mol from independent determinations by several authors for a given ion/target solvent system as shown by Marcus [31]. 

The uncertainty involved in the application of the TATB method was estimated as 1 kJ moF by Cox and Parker [40]. Indeed, if the TATB assumption is accepted for A,G" at 25°C, at which temperature it is generally applied, there is no good reason for not accepting it at any other temperature, and hence the TATB assumption should be valid also for the A,// of ions. The TPTB assumption has in more recent years replaced to some extent the TATB one, but with hardly any effect on the results. 

CsVCs, and T1+/T1 are also available [23]. They are compared in this table with values obtained by Inerowicz et al. [24] using the TATB assumption and with those obtained by Cox et al. [25] using the NUP assumption. The drawback of the polarographic method is that it is not directly applicable to the electrode potentials involving anions, say with an X /AgX, Ag electrode obtained potentiometrically. Such potentials for X=Cl and I obtained using the TATB assumption are shown in Table 8.3. Some additional values of standard electrode potentials are in the reports by Parker and coworkers and by Johnsson and Persson [27-29]. 

There are marked divergences between transfer chemical potential trends according to the Wells and TATB assumptions, and the conclusions... 

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