Solvent extraction of permanganates (Na, K) by 18-crown-6 ether from water into 1,2-dichloroethane: elucidation of an extraction equilibrium based on component equilibria.
Ion-pair formation constants (K(MLA) mol(-1) dm(3)) of Na(+)- and K(+)-18-crown-6 ether (18C6) complexes with MnO(4)(-) in water (w) were determined potentiometrically at 25 degrees C. Simultaneously, extraction constants (K(ex) mol(-2) dm(6)) of the permanganates with 18C6 from w into 1,2-dichloroethane at 25 degrees C were obtained from the spectrophotometric determination of distribution ratios of the permanganates. These K(ex) values were divided into K(MLA) and other three component equilibrium constants and thereby extraction-selectivity and -ability were discussed in comparison with corresponding metal picrate-18C6 extraction systems reported before.
Potentiometric Determination of the Ion-Pair Formation Constant of a Univalent Cation-Neutral Ligand Complex with an Anion in Water Using an Ion-Selective Electrode
formation constants of univalent metal-crown ether complexes with anions in water. This is because stabilities of the crown ether-complex cations are low in water, where the concentration of the uncomplexed metal ion is not negligible as compared with the concentration of the crown ether-complexed one. Recently, the ion-pair formation constants of alkali metal-18-crown-6 (18C6) and -its derivative complexes with picrate (Pic–) in a water phase have been determined systematically by solvent extraction.1,2 In the present study, a theoretical equation has been derived to determine newly the ion-pair formation constant (KMLX) of a crown ether-complexed metal ion (ML+) with an anion (X–) by potentiometry with a M+ion selective electrode (ISE). Then the ion-pair formation constant (KMX) of NaPic and the KMLX values of Na(18C6)Pic and Na(18C6)ClO4 were measured in water at 25 ̊C.
Individual Activity Coefficients of Ions in Aqueous Solutions
Lewis and Randall2 in 1923 published a table of 26 individual ionic activity coefficients, which has subsequently been of frequent use to chemists. The authors emphasized, however, that the presented values should be regarded as preliminary values only. In 1927 Redlich3 reprinted the same table, and no corrections were made even by Jellinek4 in his comprehensive textbook of 1930. It has been pointed out5 that the concept of individual activity coefficients cannot be defined accurately, and such coefficients may not even be determined experimentally without some supplementary definition of non-thermodynamic nature. But the concept may not the less be, and has often been, quite u ~ e f u l , ~ ~ ~ when estimating mean ionic activity coefficients in cases where great accuracy is not claimed. I t is the purpose of the present paper to present a revised and extended table of ionic activity coefficients, which has largely been computed by independent means, taking into consideration the diameter of the hydrated ions,* as estimated by various methods. For sufficiently dilute solutions one may use the well-known Debye-Hiickel formula (aqueous solution a t 25’)