Acta Chimica 87. (1975)
3. szám - ANALYTICAL CHEMISTRY - Marton Aurél–Halmos P.–Inczédy J.: Resin-Phase Concentration Dependence of Anion-Exchange Equilibria
206 MARTON et al.: RESIN-PHASE CONCENTRATION DEPENDENCE Thermodynamically meaningful equilibrium constants for a number of univalent anions were measured by Gregor et al. [7]. In some systems the selectivity coefficients varied little with the composition, while in others a marked dependence was observed. Examples of the former included systems made up of various pairs of ions from Group A: halide, acetate, iodate and nitrate, or of pairs of ions from Group B: thiocyanate, perchlorate, di- and trichloroacetate, trifluoroacetate, toluenesulphonate and naphthalenesulphonate. Examples of the systems, where the selectivity coefficient changed markedly, were made up of anion from Group A with one from Group B. This behaviour was explained by a special ion-pair cluster formation. Equilibrium selectivity coefficients for the whole range of equivalent fraction of the preferred ion were also measured by Boyd et al. [8] for the exchange of bromide writh chloride, iodide or fluoride. The connected selectivity coefficients slightly decreased with increasing resin loading. Bucher et al. [9] studied the selectivity of the exchange of chloride with perchlorate andtrichloroacetate as a function of resin composition. They found only a gentle increase in the selectivity coefficient with increasing of the chloride mole fraction in the resin. The phenomenon! was explained on the basis of the ion-water interaction the importance of which was earlier recognized by Chu et al. [10]. A statistical thermodynamic treatment of the anion—exchange equilibria was introdufced by Harvey' et al. [11]. The v alidity of the derived equation was successively proved for the exchange of chloride with sulphate, oxalate, carbonate and borate [12]. The purpose of our investigation was the experimental determination of the selecticity coefficients as a function of the equilibrium resin composition for monovalent and bivalent anions of maleic and fumaric acids. The chosen system lends itself for the study of the exchange of the monovalent and bivalent anions without a qualitative change of the chemical species and thereby the effect of the charge can be studied. Experimental Materials and solutions: Maleic (Schuchardt, München, GFR) and fumaric (Reanal, Budapest, Hungary) acids were reagent grade chemicals. Equilibrium measurements were carried out in total normalities, viz. 0.04 and 0.1. For the investigation of the monovalent anions at the total normality of 0.04 and 0.1 stock solutions of maleic and fumaric acids were prepared (0.04 and 0.1 M, resp.) by dissolving the appropriate amount of acids in water. By addition of sodium hydroxide the pH of the above stock solutions was adjusted to 4.0 and 3.7, respectively. For the investigation of the bivalent anions at total normality of 0.04 and 0.1 maleic and fumaric acid solutions (0.02 and 0.05 M, resp.) were prepared. The pH of the stock solutions was adjusted with sodium hydroxide to 8.0. Corresponding to the above total normalities the concentration of the sodium chloride stock solution was 0.04 and 0.1 iVf, resp. Ion-exchange resin. Dowex AG 1X4 (100 — 200 mesh) chloride form anion-exchange resin was used throughout. Approximately 20 g resin was placed in a 15 cm long glass filtered ion-exchange column of 3 cm in diameter. 1 M sodium hydroxide and 1 M hydrochloric acid Acta Chim. (Budapest) 87, 1975