Electrostriction partial molal volume

Let us now ask how this value could be used as a basis from which to measure the local disturbance of the water structure that will be caused by each ionic field. The electrostriction round each ion may lead to a local increase in the density of the solvent. As an example, let us first consider the following imaginary case let us suppose that in the neighborhood of each ion the density is such that 101 water molecules occupy the volume initially occupied by 100 molecules and that more distant molecules are not appreciably affected. In this case the local increase in density would exactly compensate for the 36.0 cm1 increment in volume per mole of KF. The volume of the solution would be the same as that of the initial pure solvent, and the partial molal volume of KF at infinite dilution would be zero. Moreover, if we had supposed that in the vicinity of each ion 101 molecules occupy rather less than the volume initially occupied by 100 molecules, the partial molal volume of the solute would in this case have a negative value. 

Vj is called the partial molal volume of species / [/xy is actually the partial molal Gibbs free energy, SG/dnj)TPEhn as discussed in Chapter 6, Section 6.1, and Appendix IV]. The partial molal volume of a substance is often nearly equal to the volume of a mole of that species. However, because there is in general a slight change in total volume when substances are mixed, the two are not exactly equal. Indeed, the addition of small concentrations of certain salts can cause an aqueous solution to contract —a phenomenon known as electrostriction — which in this special case results in a negative value for Vy. 

MiUero FJ (1971) Molal volumes of electrolytes. Chem Rev 71 147-176 Morris DFC (1968) Ionic radii and enthalpies of hydration of ions. Struct Bond 4 63-82 Morris DFC (1969) Ionic radii and enthalpies of hydration of ions. Struct Bond 6 157-159 Mukerjee P (1961) Ion-solvent interactions, I. Partial molal volumes of ions in aqueous solutions, II. Internal pressure and electrostriction of aqueous-solutions of electrolytes. J Phys Chem 65 740-746... 

A related matter is the electrostriction suffered by these water molecules in the first solvation sphere. One of the ways to approach it is through determination of the partial molal volumes of the ions (with various assumptions we will not go into here). These ionic partial molal volumes can be split, using the semi-empirical Hepler equation (eq. 1), into a geometric... 

Mukerjee P (1961) Ion-solvent interactions. I. Partial molal volumes of ions in aqueous solutions. II. Internal pressure and electrostriction of aqueous solutions of electrolytes. J Phys Chem 65 740-744... 

Marky LA, Kupke DW (2000) Enthalpy-entropy compensations in nucleic acids contribution of electrostriction and stmctural hydration. Meth Enzymol 323 419-441 Masterton WL, Lee TP (1970) A classical model for the low-energy electron(positron)-atomic hydrogen(l s) elastic scattering. J Phys Chem 79 1776-1782 Mathieson JG, Conway BE (1974) Partial molal compressibilities of salts in aqueous solution and assignment of ionic contributions. J Sol Chem 3 455-477 Mauzerall D, Hou J-M, Boichenko VA (2002) Volume changes and electrostriction in the primary photoreactions of various photosynthetic systems estimation of dielectric coefficient in bacterial reaction centers and of the observed volume changes with the Drude-Nernst equation. Photosyn Res 74 173-180... 

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