Static Relative Permittivity of some Electrolyte Solutions in Water and Methanol

Abstract

Experimental results are presented for the relative permittivity of several chlorides in water and methanol at 25°C measured at 5–20 MHz up to concentration of 0.1 mol dm–3. These permittivities are interpreted as the static values ε° and show in general an initial increase with concentration, followed by a decrease below the static value of the relative permittivity ε°s of the solvent. The changes in ε° with respect to ε°s are of comparable magnitude for all chlorides in water at equal equivalent concentration, with a noticeable exception for HCl which exhibits much larger decrements. The decrements in methanol relative to ε°s are larger than in water. These results for the static relative permittivity of the electrolyte solutions have been shown to be interpretable in terms of a superposition of the Debye–Falkenhagen effect and the kinetic depolarization deficiency recently proposed by Hubbard and Onsager. At concentrations ⩽2.5 × 10–2 mol dm–3 the observed increments are in fair agreement with the theoretical values according to Debye and Falkenhagen.

At higher concentrations the experimental decrements seem to follow the theoretical relation proposed by Hubbard and Onsager, at least semi-quantitatively, and after correction for the former effect. The dependence of the relative decrements on the specific conductivity of the solution and the dielectric relaxation time of the solvent, predicted by Hubbard and Onsager, has been confirmed. No definite conclusion could be reached as to whether or not the dielectric saturation effect has some influence on the observed decrements.