Ion–ion–solvent interactions in solution. Part 3.—Aqueous solutions of sodium nitrate

Abstract

The profile of the band due to the symmetric stretching vibration in the Raman spectrum of aqueous solutions of NaNO₃ has been studied as a function of concentration. Analysis based on the Fourier transform indicates that there are at least three principal components in the band. Analysis gives the positions of the three components as 1047.6, 1050.0 and 1052.0 cm^–1, with a fourth component appearing at 1070.0 cm^–1 in the most concentrated solutions. On the basis of concentration dependence and band shape these components have been assigned to the free aquated nitrate ion (1047.6), the solvent-separated ion pair (1050.0), the contact ion pair (1052.0) and ion aggregates (1070.0). Association quotients K₁ and K₂ for the two equilibria Na⁺(aq)+ NO^–₃(aq) [graphic omitted] Na⁺· H₂O · NO^–₃(aq) [graphic omitted] Na⁺· NO^–₃·(aq) are K₁= 2.7 dm³ mol^–1(0.5 mol dm^–3) and K₂= 3.3 (6 mol dm^–3).