Dielectric relaxation studies of solutions of 1:2, 2:1 and 2:2 electrolytes in water

Abstract

The complex permittivity of a series of aqueous solutions of 1:2, 2:1 and 2:2 electrolytes has been measured in the frequency range, 0.3 to 37 GHz at 21°C. For solutions of K₂SO₄, Ni(ClO₄)₂ and the nickel salt of m-benzene disulphonic acid, the experimental data are adequately described by a single relaxation time characteristic of the solvent. With solutions of NiSO₄, CuSO₄, hexammine nickel(II) sulphate and bis-ethylene diamine copper(II) sulphate, an additional Debye-type relaxation process characteristics of the salt is observed. From the amplitude of this solute dispersion, the dipole moments of the ion pairs, assumed to be responsible for it, have been calculated. Centre-to-centre distances estimated from these electric moments are all of the order of 0.4 nm and are also consistent with the values of the experimental relaxation times for the solute dispersion, provided that the ion pairs can be regarded as prolate ellipsoids, which relax by rotational diffusion at a rate which is inversely proportional to the macroscopic viscosity of pure water.