Equilibrium between micelles and simple ions, with particular.pdfVIP

EQUILIBRIUM BETWEEN MICELLES AND SIMPLE IONS, WITH PARTICULAR REFERENCE TO THE SOLUBILITY OF LONG-CHAIN SALTS. BY R. C. MURRAY AND G. S. HARTLEY (London). Received 3rd August, 1934. In 1927, Jones and Bury,l in discussing their freezing-point data for aqueous solutions of butyric acid, pointed out that these showed a sudden departure from the normal within a small range of concentra- tion, and that this was a natural consequence of the law of mass action where micelles containing a considerable number of simple molecules were formed. Later, Grindley and BuryY2 and Davies and BuryYa extended this principle to a study of the partial specific volumes of butyric acid and potassium octoate in aqueous solution and found that these properties also showed fairly abrupt changes in the neighbourhood of FIG. I. what they called the “ critical concentration for micelles.” This con- centration for potassium octoate was in agreement with the evidence from the freezing-point data of McBain, Laing and title^.^ The reason for this effect is that the concentration of micelles con- taining m simple molecules will be proportional to the mth power of the simple molecule concentration, and therefore, once it has become an appreciable fraction of the whole, will commence to increase very rapidly if m is large, as reference to the equations given later will make clear. In Fig. I the fraction of the solute existing in micellar form is Jones and Bury, Phil. Mag., 4, 841, 1927. Grindley and Bury, J . Chem. SOC., 679, 1929. Davies and Bury, J - Chem. SOC., 2263, 1930. McBain, Laing and Titley, J . Chem. SOC., 121, 6 2 2 , 1922 ; see also Randall, McBain and White, J . A m . Chem. SOC., 48, 2517, 1926. 183 P u b l i s h e d o n 0 1 J a n u a r y 1 9 3 5 . D o w n l o a d e d b y U n i v e r s i t y o f H u l l o n 0 8 / 1 0 / 2 0 1 5 1 5 : 2 3 : 3 6 . View Article Online / Journal Homepage / Table of Contents for this issue 184 EQUILIBRIUM BET