Effects of Electrolytes in Hydrophobic Systems. III. Studies with Mixtures of Electrolytes: Ion Antagonism.

Abstract

The flocculation value of a mixture of two electrolytes for an arsenic trisulfide sol can be computed additively, if the precipitating power of each of the electrolytes is of the same order of magnitude (4), while, if the electrolytes differ markedly in their precipitating power, as do potassium chloride and barium chloride, the flocculation value of the mixture is greater than the additive value (7).The phenomenon of ion antagonism has been observed for a number of electrolyte pairs with several colloidal systems, e.g., Odén's sulfur sol (1), copper ferrocyanide sol (6), mercuric sulfide sol (3) and selenium sol (3). The explanation offered by Freundlich and Scholz (1), namely, that hydration is a critical factor in determining ion antagonism, has been evaluated by Weiser (7), who has pointed out that other factors also must be considered: (1) the antagonistic effect of each precipitating ion on the adsorption of the other, and (ß) the stabilizing influence of the ions having the same charge as the sol. Kruyt and van der Willigen (3) correlated flocculation data with electrophoretic measurements and reached the conclusion that, whenever a salt raises the charge (mobility) of the particles, its addition also will raise the flocculation value of a second salt.The present study is concerned with the electrophoretic and the coagulating behaviors of the salt pairs potassium chloride-barium chloride and potassium chloride-chromium chloride with a manganese dioxide sol and an arsenic trisulfide sol. The investigation is the third of a series of reports which have dealt with anomalies of monovalent ions as applied to the above colloidal systems. The same stock samples of sols were used throughout the investigations and the experimental methods wrere the same. results Flocculation data for the two sols, each at three different concentrations, are given in tables 1 and 2 in terms of millimoles of. electrolyte per liter. The experiments wrere conducted by adding 2 cc. of sol to 3 cc. of electrolyte mixture. The amounts of barium chloride and of chromium chloride required to coagulate the colloidal systems were determined when each of these electrolytes was present with 25, 50, and 75 per cent of the flocculating concentration of potassium chloride.