Ion-solvent interactions and Viscosity B-Coefficients of aqueous solutions of some ionic solutes at different temperatures


Oyebade, A; Omodara, N. B and Oloyede, H. O.

Adeyemi college of education, Ondo


Abstract: Viscosities of various concentrations of the solutions of sodium iodate, sodium chromate and trisodium phosphate were measured at the temperature range of 25-40oC. The objectives were to examine the effects of the charge and size of the anions on solute-solvent interactions; determine the extent of perturbation of the solvent structure by the solutes; and determine the contribution of each ion to the solution B-coefficients. The overriding aim was to understand the composite solute-solvent microscopic structure. Viscosities and densities of the various concentrations of the salt solutions were measured at constant temperatures of 25, 30, 35 and 40oC using a calibrated Cannon-Fenske viscometer and a standard pycnometer respectively. Data obtained were fitted into different models for the evaluation of the apparent molar volumes at infinite dilution, the B-coefficients, the molar expansibilities, the Hepler’s constants and some thermodynamic quantities associated with viscous flows. The B-coefficients obtained from the Jones-Dole and Mahuiddin equations were respectively in the range 0.1654-1.8274 (dm3 mol-1) and 0.1327-1.6788 (dm3 mol-1). The Mahuiddin model was adjudged to be more accurate from the high linearity of the plots at fairly high concentrations. The ionic B-coefficients obtained for the anions were , and , giving the order , and the trend implicated the surface charge of the ions to cause the extent of solute-solvent interactions. A-coefficients obtained from the Jones-Dole model for the solutes decreased with temperature increase, indicating weak ion-ion interactions in the systems arising from greater thermal agitation. The apparent molar expansibilities were negative within the temperature range. The Hepler’s constants were positive, suggesting that all the solutes were structure makers. The activation energies of viscous flow were consistent with the number and kind of ions in solution. On the strength of the B-coefficients, the derivative of the B-coefficients with temperature, the Hepler’s constants and the activation energies per mole of solute, the three salts were classified as structure makers of the solvent with the tendency of the solute to modify the structure of the solvent increasing as the charge of the anions increases.

Keywords: Ion-solvent interactions, Structure maker/breaker, Viscous flows, Perturbation.