Dielectric relaxation of aqueous Na₂CO₃ solutions

Abstract

The complex dielectric permittivity of aqueous sodium carbonate solutions (0.05⩽c/mol L^-1⩽2.5) has been determined in the frequency range 0.2⩽ν/GHz⩽20 at 25.0°C with a commercial dielectric measurement system based on a vector network analyser. A superposition of three Debye relaxation processes was necessary to fit the complex permittivity spectra. The slow and intermediate dispersion steps are assigned to double solvent separated (2SIP) and solvent-shared (SSIP) NaCO₃^-(aq) ion-pairs respectively. The absence of contact ion-pairs was confirmed by Raman spectroscopy. The fast process is assigned to the collective relaxation of the solvent. Equilibrium constants for the formation of NaCO₃^-(aq) were determined from the ion-pair dispersion amplitudes. The effect of Na₂CO₃ concentration on the water dispersion amplitude allowed effective solvation numbers to be deduced.

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