Apparent Molar Volume and Apparent Molar Expansibility of Tetraethyl-, Tetra-n-propyl-, Tetra-n-butyl-, and Tetra-n-pentylammonium Cyclohexylsulfamates in Aqueous Solution†

Cveto Klofutar, Jaka Horvat and Darja Rudan-Tasič*
Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia

The apparent molar volume of tetraethyl-, tetra-n-propyl-, tetra-n-butyl, and tetra-n-pentylammonium cyclohexylsulfamates was determined from the density data of their aqueous solutions at 293.15, 298.15, 303.15, 313.15, 323.15 and 333.15 K. From the apparent molar volume the partial molar volume of the salts and water was determined. The limiting apparent molar volume and apparent molar expansibility were apportioned into their ionic components. The limiting apparent molar volume of the salts was found to be a linear function of the cation molecular weight. The partial molar ionic volumes at infinite dilution were treated by a model proposed by Marcus. From the second derivative of the limiting apparent molar volume with temperature it was found that the investigated solutes behave as structure-making ones in water. The packing density of the ions in solution were evaluated and compared with the corresponding data for tetra-n-alkylammonium halides. The density of aqueous solutions of the investigated salts can be adequately represented by an equation derived by Redlich.

Keywords: Density data, partial molar volume, expansibility, cyclohexylsulfamates, aqueous solutions.