Volumetric studies of some electrolytes in water and in aqueous sodium dodecylsulfate solutions at different temperatures

The apparent molar volumes (phi(v)) of KCl, KNO3, MgCl2, and Mg(NO3)(2) have been determined in water and in aqueous sodium dodecylsulfate solutions from density measurements at 303.15, 308.15, 313.15, 318.15, and 323.15 K. The limiting apparent molar volumes (phi(0)(v)) and experimental slopes (S-v) were derived from the Masson equation. The partial molar volume transfer (Delta(V) over bar (tr)) of the electrolytes were obtained from limiting apparent molar volume data from water to aqueous sodium dodecylsulfate solutions and have been interpreted in terms of ion-ion, hydrophilic-hydrophilic, and hydrophobic-hydrophobic interactions on the basis of a co-sphere overlap model. It is shown that the transfer volumes (Delta(V) over bar (tr)) are positive and increase with increasing sodium dodecylsulfate concentration for all electrolytes. The structure making or breaking capacities of the electrolytes have been inferred from the sign of [partial derivative(2)phi(0)(v)/partial derivative T-2](p), i.e., the second derivative of the limiting apparent molar volume with respect to temperature at constant pressure. In water, KCl and KNO3 exhibit structure breaking and MgCl2 and Mg(NO3)(2) exhibit structure making behavior. All the studied electrolytes were found to act as structure makers in aqueous sodium dodecylsulfate solutions.