Apparent Molar Volume and Apparent Molar Expansibility of Sodium Saccharin, Potassium Acesulfame and Aspartame

Cveto Klofutar, Jaka Horvat and Darja Rudan-Tasič

Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia

The apparent molar volume of sodium saccharin, potassium acesulfame and aspartame 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. Solutions of sodium saccharin and potassium acesulfame were treated as 1:1 strong electrolyte, while aspartame was considered as a non-electrolyte. From the apparent molar volume, determinated at various temperatures, the limiting apparent molar expansibility was calculated. The limiting apparent molar volume and expansibility of ionic solutes were divided into their ionic components and discussed in terms of the various effects of the ion in solution on the structure of water. The limiting apparent molar volume of aspartame was discussed in terms of the scaled particle theory. The density of the investigated aqueous solutions can be adequately represented by an equation derived by Redlich. The coefficients of thermal expansion of the investigated solutions at 298.15 K were calculated and are presented graphically.
The thermal expansion coefficient, α* defined as
α*=1/V02F(JV02F/JT)P and their temperature dependence was estimated.
It was shown that α* of electrolyte solutes is greater than that of aspartame and that α* of ionic solutes decreases linearly with increasing temperature, while α* of aspartame shows a slight increase with temperature. The limiting apparent molar volume and expansibility were correlated with the relative sweetness of the sweeteners investigated and some other alternatives.

Key words: density data, expansibility, sweeteners, aqueous solutions