Method for analysis of the composition of acid soaps by electrolytic conductivity measurements

Here, we propose a method for determining the stoichiometry of acid-soap crystallites. The method is based on dissolving the crystallites in water at an appropriate working temperature, followed by measurement of the electrolytic conductivity of the obtained solutions. The working temperature is chosen in such a way that the only precipitate in the solutions is that of carboxylic acid, whereas the carboxylate salt is dissociated, and its content in the dissolved crystals determines the solution's conductivity. In the theoretical model for data interpretation, we took into account the dependence of the molar conductance on the ionic strength. The method was applied for determining the stoichiometry of acid-soap crystals collected from solutions of potassium myristate (tetradecanoate) at 25 °C. The crystals were dissolved in water at working temperature of 40 °C, at which the conductivity was measured. The stoichiometry of all samples determined in the present study coincides with that independently obtained by another method that is based on in situ pH measurements.

The acid-soap crystallites that are spontaneously formed in carboxylate soap solutions represent complexes of j molecules carboxylic acid and n   molecules neutral soap. A method is proposed for determining their stoichiometry, j:nj:n, by electrolytic conductivity measurements.Figure optionsDownload as PowerPoint slide