Aqueous solution data polarizability

Three years later, Wasastjema was able to present a table with more accurate radii for 16 ions, including 0 , F, Na", and Mg" (Table 3) [36]. Wasastjema fixed the ratio between the radius of an alkali metal cation and the radius of the isoelectronic halide anion (for instance, the ratio between the radii of Na" and F ) using polarizability data from aqueous solutions. The polarizabilities of the halide anions were first determined under the assumption that the hydrogen ions do not contribute significantly to the molar polarizabilities of dissolved hydrogen halides. The polarizabilities of the cations could then be obtained from measurements on the salts. Molar polarizabilities are roughly proportional to the ionic volumes, and Wasastjema fixed the radius ratio r+/r as the fourth root of the polarizability ratio of the two ions (Table 3). 

The electrical double layer at pc-Zn/fyO interfaces has been studied in many works,154 190 613-629 but the situation is somewhat ambiguous and complex. The polycrystalline Zn electrode was found to be ideally polarizable for sufficiently wide negative polarizations.622"627 With pc-Zn/H20, the value of Eg was found at -1.15 V (SCE)615 628 (Table 14). The values of nun are in reasonable agreement with the data of Caswell et al.623,624 Practically the same value of Eff was obtained by the scrape method in NaC104 + HjO solution (pH = 7.0).190 Later it was shown154,259,625,628 that the determination of Eo=0 by direct observation of Emin on C,E curves in dilute surface-inactive electrolyte solutions is not possible in the case of Zn because Zn belongs to the group of metals for which E -o is close to the reversible standard potential in aqueous solution. 

Ggawa, T. and Satoh, K. Density, partial molal volume, refractiye index, polarizability, and viscosity of concentrated and saturated aqueous solutions of Rochelle salt, J. Chem. Eng. Data, 21(l) 33-35, 1976. 

In the case of the study of the adsorption of molecular solutes at the polarizable interface, different tactics are often employed in data analysis. Suppose a study of the adsorption of pyridine is carried out at the mercury solution interface from an aqueous solution containing KCl. The Gibbs adsorption isotherm for this system using a reference electrode reversible to the CU anion is... 

In the following discussion some important features of the experimental results for anion adsorption are presented. Emphasis is placed on data obtained at mercury electrodes in aqueous solutions. This simply reflects the fact that a large fraction of the existing data were obtained for these systems. This is followed by a presentation of the theory applied to ion adsorption at polarizable interfaces. 

The effect of the solvent is usually modelled either by the use of the Onsager s self consistent reaction field (SCRF) [20] or by the polarizable continuum method (PCM) [21]. With regard to the relative stability of cytosine tautomers in aqueous solution, these methods provided results [14,15] which, in spite of some discrepancies, are in reasonable agreement with experimental data [3]. However, continuum-based methods do not explicitly take into consideration the local solvent-solute interaction which is instead important in the description of the proton transfer mechanism in hydrogen-bonded systems. A reasonable approach to the problem was recently proposed [22,23] in which the molecule of interest and few solvent molecules are treated as a supermolecule acting as solute, while the bulk of the solvent is represented as a polarizable dielectric. 

Cu crystallizes in the fee system. The experimental data for single-crystal CUIH2O and for PC Cu are controversial [2-5,7,44,45[. The first studies with Cu(lll), Cu(lOO), Cu(llO), and PC Cu in surface-inactive electrolyte solutions show a capacitance minimum at E less negative than the positive limit of ideal polarizability of Cu electrodes. More reliable values of cr=o for Cu single-crystal faces have been obtained by Lecoeur and Bellier [44] with EP Cu(l 11) and Cu(lOO) (Table 1). Eoresti etal. [46] have found =o = -0.93 0.01 V (SCE) for the Cu(l 10)-aqueous solution interface, and the validity of the GCSG model has been verified. As for Zn single-crystal electrodes, reliable values of cr=o have been obtained indirectly from the dependence of the adsorption-desorption peak... 

The degree of polarizability of system can be found from the data calculated by Le Hung [25] with the use of Eqs. (16) and (17). In the equilibrium state of the interphase between the solutions of 0.05 M LiCl in water and 0.05 M TBATPhB in nitrobenzene, the concentrations of Li and CL in the organic phase lower than 10 M, and the concentrations of TBA and TPhB in the aqueous phase are about 3 x 10 M each [3]. These concentrations are too low to establish permanent reversible equilibria. They are, however, significantly higher compared to those of the components present in the mercury-aqueous KF solution system [20]. 

The Wilhelmy plate technique has also been modified to measure surface or interfacial tensions under special conditions. By way of illustration we mention the application to the measurement of electrocapillanj curves for the mercuiy-aqueous electrolyte solution interface by Montgomery and Anson ), extending earlier work by Smith ). Electrocapillary curves are plots of y as a function of the potential applied across the interface, which should be polarizable. In fig. II.3.48 we already gave a few such curves. Montgomery and Anson found that their curve in 10 2 M NaF agreed within 0.005 mN m- with data obtained using the maximum bubble pressure. 

The connectivity indices and the polarizability parameters, however, relate a solutes solubility directly to its molecular structure, and thus could be more useful in the design and evaluation of new chemicals. A particular drawback of the polarizability parameter used here is that, unlike the LSER descriptors, it is not universally applicable to all solute-solvent interactions. It has to be defined and optimized for each property being studied. The log p descriptor is purely empirical, and does not poru ay any direct mechanistic significance in relation to the solutes molecular structure. Further, since Model 1 is significantly improved by including melting point data, it can be noted that log p alone docs not encode sufficient information relating aqueous solubility. 

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