Partial Molal Volumes and Expansibilities of Sodium Salts of some Fatty Acids in Water at Various Temperatures

Department of Chemistry, Visva-Bharati University, Santiniketan-731 235

Manuscript received 12 April 1983, revised 3 September 1984, accepted 6 February 1986

The partial molal volumes ($\varphi$^o_$\vartheta$$\equiv$ $\overline{V_2^0}$) of the sodium salts of formic acid, acetic acid, propionic acid, n-butyric acid and n-valeric acid have been obtained from density measurements (pycnometrically) at 25, 35, 45 and 55°. The partial molal expansibilities (E°) have also been calculated from the temperature dependence of partial molal volumes. Both partial molal volumes and expansibilities have been dissected into ionic contributions using the additivity principle. The partial molal volumes of the hydrophobic anions have been found to vary in the order, n-valerate > n-butyrate > propionate > acetate > formate, and the expansibilities vary in the same order.

The partial molal volumes at different temperatures do not present a clear picture about the structure altering properties of these solutes, but the expansibilities do.