Some Important Properties of Polar Solvents

A number of properties, including dielectric properties, should be considered in assessing a given polar solvent. Important bulk properties are density, vapor pressure, thermodynamic properties related to vaporization, heat capacity, viscosity, compressibility, and surface tension. Some of these are summarized in table 4.1 and are discussed briefly in this section. 

Water is unique among polar solvents in that it is a small molecule with a low molar volume. As a result, the concentration of water in pure water is 55.5 M. This means that the mole fraction of water in dilute aqueous solutions is close to one, and the partial molar quantities in these solutions are close to the corresponding quantities for the pure solvent. Other solvents have considerably higher molar volumes, and therefore, lower concentrations in the pure solvent. The 

Solvent Molecular Mass /g moP Molar Volume /cm mop Enthalpy of Vaporization /kJ mop Entropy of Vaporization /K- moP Molar Heat Capacity /J K mop  

The dielectric properties of the solvents considered here are summarized in table 4.2. These properties are important in evaluating the solvation of ions in polar solvents under both static and dynamic conditions. The relative permittivity of a solvent at high frequencies, Sop, can be calculated from the refractive index, nop, the relationship being 

Some molecular properties of polar solvents are summarized in table 4.3. The dipole moment and molecular polarizability are the molecular parameters which lead to the solvent permittivity. The other parameters listed are the molecular diameter and the Lennard-Jones interaction energy, Elj. These are of interest in assessing the role of van der Waals forces in determining the properties of a polar liquid. 

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