Abstract
Extraction constants (Kex & Kex±) for the extraction of silver picrate (AgPic) by benzo-18-crown-6 ether (B18C6) into 1,2-dichloroethane (DCE) were determined at 298 K and various ionic strength (I)-values of a water phase with or without excess HNO3. Here the symbols, Kex and Kex±, were defined as [AgLPic]DCE/P and [AgL+]DCE[Pic−]DCE/P with P = [Ag+][L]DCE[Pic−] and L = B18C6, respectively; [ ]DCE refers to the concentration of the corresponding species in the DCE phase at equilibrium. Simultaneously, KD,Pic (= [Pic−]DCE/[Pic−]) and K1,DCE (= Kex/Kex±) values for given I and IDCE values were determined, where the symbol IDCE shows I of the DCE phase. Also, equilibrium potential differences (Δφeq) based on the Pic− transfer at the water/DCE interface were obtained from the analysis of the KD,Pic [= KD,PicS exp{−(F/RT) Δφeq}] values; the symbol KD,PicS shows KD,Pic at Δφeq = 0 V. On the basis of these results, I dependences of logKex and logKex± and IDCE ones of logK1,DCE and logKex± were examined. Extraction experiments of AgClO4 and AgNO3 by B18C6 into DCE were done for comparison. The logKex±-versus-Δφeq plot for the above Ag(I) extraction systems with Pic−, ClO4−, and NO3− gave a good positive correlation.
Highlights
It is well known that crown compounds (L) extract alkali and alkaline-earth metal ions (Mz+, z = 1, 2) from water (w) into various diluents [1,2,3,4]
I/ 1 + I − 0.3I = −0.5 + 2×116 IDCE. The magnitudes of these changes in logKex± or logKex with I or IDCE were insignificant in practical separation
It was suggested that the style of M(I) employed in the extraction experiments with L, either the simple salt MPic or the mixture of MX with HPic and excess HX, largely control whether the logKD,Pic values are dependent on the log(IDCE /I ) ones or not
Summary
It is well known that crown compounds (L) extract alkali and alkaline-earth metal ions (Mz+ , z = 1, 2) from water (w) into various diluents [1,2,3,4]. The two representative constants, Kex and Kex± , for the extraction of a univalent metal salt (MI A) by L have been defined as [MLA]org /P [2,3]. The subscript ”org” denotes an organic phase and A− does a univalent pairing anion. For the latter Kex± , its thermodynamic equilibrium constants have been reported [4]. For the former Kex , its thermodynamic treatment seems to be few
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