Volumetric and viscometric studies on sodium nitrate and potassium nitrate in aqueous and H2O-urea solutions

Abstract

Density and viscosity of NaNO3 and KNO3 in aqueous and in H2O-urea solutions were determined as a function of electrolyte concentrations at 308, 313, 318, 323, and 328 K, respectively. The apparent molal volume (φ v ) of the electrolytes were found to be linear functions of the square root of the solute molality (b). The φ v and data were fitted to the Masson equation [1] by the least square method to obtain the apparent molar volume at infinite dilution (φ v ^), which is practically equal to the partial molar volume . The viscosity coefficients A and B were calculated on the basis of the viscosity of the solutions and the solvent concerned using the Jones–Dole [2] equation. The activation parameters for viscous flow (ΔG ≠, ΔS ≠, and ΔH ≠) were calculated according to Eyring [3]. The values of for the two systems were also calculated from B-coefficient data. The results were found to be of opposite nature in the two electrolyte systems. Where sodium nitrate showed structure making behaviour both in aqueous and in H2O-urea solutions, KNO3 showed structure breaking behaviour in aqueous solutions and structure making behaviour in 5 molal H2O-urea solutions in the studied temperature range. The behaviour of these two electrolytes in aqueous binary and in aqueous-urea ternary systems are discussed in terms of charge, size, and hydrogen bonding effects.