The extraction of antimony from an aqueous halide medium into an organic solvent has been frequently used for both the separation and spectrophotometric determination of antimony. The methods for the solvent extraction-photometric determination of antimony(V) based on the extraction of the ion-association complexes of the chloride-complex (SbCl6 -) of antimony(V) with cations of some dyes, such as Malachite Green, 1 Brilliant Green, 1-4 Crystal Violet, 1,2,5 Ethyl Violet 2 and Rhodamine B [6][7][8][9][10][11][12] have been reported. However, the equilibrium for the solvent extraction of the ion associates of hexachloroantimonate(V) has not been studied.In the present work, the extraction constants (log Kex) for the ion associates of hexachloroantimonate(V) ion with various quaternary ammonium ions distributed between an aqueous and four organic phases (chloroform, benzene, toluene and carbon tetrachloride) were determined and correlated with the number of carbon atoms in the quaternary ammonium ions. The extractability of hexachloroantimonate(V) was also considered based on those of other metal-halogeno complex anions. [13][14][15][16][17][18] Experimental ApparatusThe apparatus for recording spectra and absorbance measurements, horizontal shaking and phase separation after extraction were described in a previous paper. 19 ReagentsThe supplier and purity of quaternary ammonium ions, and the preparation of the quaternary ammonium ion solutions were as described in a previous paper. 15A standard antimony(III) solution (4 × 10 -4 M) was prepared by dissolving antimony(III) chloride with 8 M hydrochloric acid solution. Hydrochloric acid was used for the formation of a antimony(V)-chloro complex. Cerium(IV) sulfate solution was prepared by dissolving with a diluted sulfuric acid solution, and was employed as the oxidant for the oxidation of Sb(III) to Sb(V). A hydroxylammonium chloride aqueous solution was employed as the reductant for the reduction of any excess cerium(IV) sulfate. Commercially available chloroform, benzene, toluene and carbon tetrachloride were used without further purification, and were saturated with distilled water before use. Standard procedure for a stoichiometry measurementOne milliliter of a 4 × 10 -4 M antimony(III) solution was transferred to a 25 ml stoppered test-tube; then, 0.5 ml of a 9.44 M hydrochloric acid solution, 0.5 ml of a 2 × 10 -2 M cerium (IV) sulfate solution (in 6 M sulfuric acid), 1 ml of a 15 M sulfuric acid solution, 2 ml of concentrated hydrochloric acid solution, 0.5 ml of a 0.2 M hydroxylammonium solution and an appropriate amount of aqueous quaternary ammonium salt solution were added. The solution was diluted to 6 ml with distilled water. The aqueous solution was mechanically shaken with 6 ml of an extracting solvent for 20 min at 25˚C. After centrifugation of the mixture, the absorbance at 280 nm of the aqueous phase was measured for the determination of antimony. Calculation of the extraction constantsIn the chloride-ion concentration of 6 M, the antimony(V)-chl...
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