Ultrasonic behaviour of the system magnesium soap-benzene and methanol

Abstract

The colloid chemical behaviour and the micellar features of magnesium caprylate and caprate in benzene-methanol mixtures (v:v = 9:1,1:1,1:4) were investigated by ultrasonic velocity and density measurements at 40° ± 0.1. The critical micelle concentrations (c.m.c.) depend upon the composition of solvent mixtures and are found to decrease with the increasing chain length of the soap anion. Acoustic parameters such as adiabatic compressibility, intermolecular free length show deviations at different concentrations indicating effective soap-binary solvent interaction. The specific acoustic impedance and molar sound velocity increase, while adiabatic compressibility and intermolecular free length decrease with increasing soap concentration. With respect to soaps, the values of specific acoustic impedance and ultrasonic velocity follow the order Caprylate > Caprate. The result reveals that soaps behave as weak electrolytes in dilute solutions and show significant interaction between the soap-solvent molecules. The data confirm that the behaviour of the soap below and above 1:1 is quite different.