Volumetric and Viscometric Studies on Sodium Nitrate and Potassium Nitrate in Aqueous and H2O-urea Solutions
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 (φv) of the electrolytes were found to be linear functions of the square root of the solute molality (b). The φv and \(\) data were fitted to the Masson equation  by the least square method to obtain the apparent molar volume at infinite dilution (φv^), 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  equation. The activation parameters for viscous flow (ΔG≠, ΔS≠, and ΔH≠) were calculated according to Eyring . 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.
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