Effect of magnesium chloride (2:1 electrolyte) on the aqueous solution behavior of some saccharides over the temperature range of 288.15–318.15 K: a volumetric approach

Abstract

Infinite-dilution standard partial molar volumes, V 2 0 , for various mono-, di-, and trisaccharides, and their derivatives (methyl glycosides) at molalities ranging from 0.04 to 0.12 mol kg −1 in aqueous solutions of magnesium chloride of 0.5, 1.0, 2.0, and 3.0 mol kg −1, have been evaluated over a range of temperatures from 288.15 to 318.15 K by density measurements employing a vibrating-tube densimeter. These data have been utilized to determine the corresponding standard partial molar volumes of transfer, Δ t V 2 0 , of saccharides and methyl glycosides from water to aqueous magnesium chloride solutions. The Δ t V 2 0 values have been found to be positive, and their magnitudes increase with an increasing concentration of magnesium chloride in all cases. Partial molar expansion coefficients, ( ∂ V 2 0 / ∂ T ) P and second derivatives thereof, ( ∂ 2 V 2 0 / ∂ T 2 ) P have been estimated. The magnitude of V 2 0 values increases with an increase in temperature, indicating that hydration effects in solutions are strongly sensitive to temperature. Pair and higher order volumetric interaction coefficients ( V AB, V ABB) have also been obtained from Δ t V 2 0 values by using the McMillan–Mayer theory. The various parameters have been discussed in terms of the solute (saccharide or methyl glycoside)–co-solute (magnesium chloride) interactions and are thus used to understand the mixing effects due to these interactions. These results have been compared with those earlier reported in the presence of electrolytes. An attempt is made to interpret the volumetric properties data in terms of the stereochemistry of the solutes.