MEAN ACTIVITY AND THE ACTIVITIES OF THE SEPARATE IONS OF SODIUM DECANOATE ABOVE AND BELOW THE CMC DETERMINED BY A SURFACTANT SELECTIVE SILVER-SILVER DECANOATE ELECTRODE

The mean activity a±, and the mean concentration, m±, of sodium decanoate have been determined at concentrations above and below the critical micelle concentration (CMC) at 25°C, using a surfactant selective silver/silver decanoate electrode and a cation exchange membrane electrode responsive to the sodium ions. It was found that both a± and m± increase somewhat above the CMC. The activity of the singly dispersed decanoate ions and the sodium ions were also determined separately above and below the CMC, using a calomel reference electrode. It was found that the activity of the free surfactant ions decreased above the CMC. The fraction of associated counterions was found to increase with increasing concentration of the surfactant. © 1979.