Electrical conductance of some paraffin-chain salts in propanol—water and propionic acid—water mixtures

Abstract

Measurements have been carried out with aqueous solutions of 1- and 2-propanol and propionic acid, respectively, with the object of studying the effect of changes in polar third components of related structure on the soap—water systems. The addition of propionic acid does not alter the form of the conductance function; the Λ − √ C curve exhibits a normal break point. Replacement of the carboxyl group by the hydroxyl, however, produces a maximum in the plot. When present in small amounts the three additives lower the critical concentration and thus favor micelle formation. Larger additions of the acid raise the critical concentration for micelle formation. With increasing alcohol concentration the effects are complex. As the temperature is raised the critical concentration of sodium dodecyl sulfate in water passes through a minimum. In the alcohol—water mixtures this minimum occurs at lower temperatures than for pure water. Values for the heats of aggregation have been calculated from these observations.