Interactions of Ions with Other Solutes

Solvated ions interact in solution with other solutes, whether the latter are ions of the same charge sign (they repulse each other electrostatically), ions of the opposite sign (they attract each other), or non-ionic solutes. If the other solute is non-ionic, it may be non-polar (ions salt such solutes out) or polar (where several kinds of interaction may take place). In some cases, such interactions may cause changes in the solvation structure and dynamics of the ions in question, and such issues are dealt with in this chapter. 

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The problan of assignment of the so-called absolute individual ionic values to these infinite dilution electrolyte data is solved mainly on the basis of chemical intuition (Chapter 4) that can be assisted by the results from computer simulations. Once individual ionic values of their properties in a given solvent (or solvent mixture) at a given thermodynamic state [tanperature and pressure, usually specified as 298.15 K (25 C) and O.lMPa (less commonly now latm=0.101325MPa)] have been established, they may be compared with other properties of the ions (e.g., their sizes) or with theoretical expectations (models). The latter are the main incentives to obtaining the absolute values. Such comparisons and correlations provide insights into the ion-solvent interactions that take place and form the basis for understanding interactions of ions with other solutes, be they ionic themselves or nonionic. 

Ions in solntion play important roles in many fields of science and the interaction of the ions with the solvent (their solvation) or with solvent mixtures (leading to preferential solvation) affects the nse of such solution. So does also the interaction of ions with other solutes, be they other ions, leading to ion association, or nonionic solutes, causing them to be salted-ont (or -in, in rare cases). 

This interface is critically important in many applications, as well as in biological systems. For example, the movement of pollutants tln-ough the enviromnent involves a series of chemical reactions of aqueous groundwater solutions with mineral surfaces. Although the liquid-solid interface has been studied for many years, it is only recently that the tools have been developed for interrogating this interface at the atomic level. This interface is particularly complex, as the interactions of ions dissolved in solution with a surface are affected not only by the surface structure, but also by the solution chemistry and by the effects of the electrical double layer [31]. It has been found, for example, that some surface reconstructions present in UHV persist under solution, while others do not. 

To investigate ionic equilibria so as to obtain information about the interactions of ions with each other, with non-ionic solutes and with the solvent. 

For any practical application of polyelectrolyte brushes the influence of multivalent ions, hydrophobic ions, and other polyelectrolyte molecules present in a contacting solution on to the structure of the surface-attached layers or the cylindrical polyelectrolyte brushes are of utmost importance. In particular, study of the interaction of brushes with other polyelectrolyte molecules in solution might open an avenue for the understanding of interaction of proteins or other charged biomolecules such as DNA, as a special form of charged macromolecules, with charged surfaces. It has become clear that not only the influence of the surface on to the conformation of the protein, but also the influence of the protein on the structure of the polymer layer is important. 

The interactions of ions with water molecules and other ions affect the concentration-dependent (colligative) properties of solutions. Colligative properties include osmotic pressure, boiling point elevation, freezing point depression, and the chemical potential, or activity, of the water and the ions. The activity is the driving force of reactions. Colligative properties and activities of solutions vary nonlinearly with concentration in the real world of nonideal solutions. 

The interactions between charged defects may be accounted for by using the Debye-Huckel theory in analogy with the interactions of ions in aqueous solutions. This requires knowledge of the relative dielectric constant, the smallest distance between charged defects, and other parameters for the solid. Debye-Huckel corrections have, for instance, been worked out and tested for cation vacancy defects in metal-deficient Coi-yO and Nii-yO. At infinite dilution the... 

The approach introduced by E. A. Guggenheim and employed by H. S. Harned, G. Akerlof, and other authors, especially for a mixture of two electrolytes, is based on the Br0nsted assumption of specific ion interactions in a dilute solution of two electrolytes with constant overall concentration, the interaction between ions with charges of the same sign is non-specific for the type of ion, while interaction between ions with opposite charges is specific. 

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