Ion-pair and solvent relaxation processes in aq. Na2SO4 solutions

Abstract

The complex dielec. permittivity of aq. sodium sulfate solns. (0.025 ≤ c/mol dm-3 ≤ 1.6) was detd. in the frequency range 0.2 ≤ ν/GHz ≤ 20 with a com. dielec. measurement system based on a vector network analyzer. The dielec. permittivity spectra were supplemented with interpolated literature data at 12 ≤ ν/GHz ≤ 89. To fit the spectra, a superposition of three Debye relaxation processes was necessary. The slow and intermediate dispersion steps were assigned to the tumbling motion of doubly solvent-sepd. (2SIP) and solvent-shared (SSIP) NaSO4- ion pairs, resp. The fast process, of amplitude S3, was explained with the collective relaxation of the solvent. Effective solvation nos. were deduced from the effect of Na2SO4 concn. on S3. From the ion-pair dispersion amplitudes, the following data were obtained: S1 and S2, the concns. c2SIP and cSSIP, and, eventually, the overall stoichiometric stability const., βNaSO4-.