Ion Pair Formation in NaNO3/D2O Solutions: Raman and Infrared Spectra, Partial Molal Volumes, Conductance, and Viscosity

Abstract

Laser Raman and infrared vibrational spectra of solutions of NaNO3 in deuterium oxide reveal the presence of both [Formula: see text] ion pairs and solvated nitrate ions. The degree of association has been measured. The concentration quotients are remarkably independent of concentration and almost equal to the thermodynamic association constant, 0.060 ± 0.006 kg mol−1 at 25.0 °C. The latter quantity was obtained by an extrapolation procedure, taking account of the activity coefficients. Values are reported for the activity coefficient of the ion pair. Interpretation is also considered in terms of a place-exchange equilibrium involving the solvent. Vibrational assignments are made to the two forms of nitrate ion present. Density, partial molal volume, conductance, and viscosity data are also presented and discussed in terms of the reported constitution.