Volumetric properties of aqueous solutions of alkali halides

Abstract

The density of aqueous solutions of LiF, NaF, or KF, at room temperature, is measured as a function of the concentration. The measurements, together with corresponding data available on other alkali halides, are used to illustrate the concentration dependence of the apparent molar volume of the electrolytes in aqueous solution. The data is in accordance with the conception that an essential, negative contribution to the volume is due to a progressive hydration of the ions upon dilution (i.e. with increasing water concentration). The peculiar behaviour of the Li+-salts, compared with the other alkali halides, is associated with the small size of the Li~-ion compared with a water molecule.

What is the fundamental ion-specific series for anions and cations? Ion specificity in standard partial molar volumes of electrolytes and electrostriction in water and non-aqueous solvents

“…Some of these methods rely on the ionic radii to estimate the intrinsic molar volume of an electrolyte, we think these values are sensitive to the assumptions of the model chosen so we do not follow this approach. According to Marcus, 58 reasonable estimates (independent of the ionic radii) of the intrinsic molar volume of an electrolyte in solution are the ones proposed by Pedersen et al , 72 who extrapolated the intrinsic volume of the molten electrolyte down to room temperature (assuming the expansivity coefficient is constant), and by Marcus, 73 who calculated the intrinsic volume for highly soluble salts, by extrapolating their partial molar volumes in concentrated solution up to a concentration where all the water present is completely electrostricted. If this information was not available, an acceptable estimation of the intrinsic molar volume was obtained from the crystal molar volume V cryst (eqn (4)), which was first used by Padova: 74 where V cryst is the molar volume of the crystalline electrolyte, M i the molar mass of the electrolyte and ρ salt is the density of the salt.…”

“…Therefore, for the purpose of this work, we used the estimates calculated by Pedersen et al 72 when available, otherwise we used the ones given by Marcus in his 2010 paper, 73 and V cryst as the last resort. These criteria were used to determine V i intr for all the electrolytes used in this work.…”

Electrostriction in Electrolyte Solutions

“…Padova 52 listed the molar volumes of the crystalline salts, V cryst = M salt /F salt , in a table of intrinsic volumes and compared them with values obtained by various methods but without specifying them. In a rarely mentioned paper, Pedersen 53 employed the molar volume of the molten alkali metal halides extrapolated with assumed constant values of the expansibilities down to ambient temperatures, V melt = M salt /F salt extrap , as a measure of their intrinsic volumes. He argued that the volume occupancy in crystals is constrained by the crystal structure and that the real intrinsic volume of ions in solution is more akin to that of the molten salt, albeit requiring a very long extrapolation down from the melting points.…”

A Model for Calculating the Heat Capacity of Aqueous Solutions, with Updated Density and Viscosity Data

“…Density data are available only at 25 °C, and therefore conversions of kinematic to dynamic viscosities at other temperatures are subject to systematic errors. Perdersen 260 has detailed data available for 25 °C, with more than 150 densities at different concentrations. Only some of the data are used here.…”