Silver(I) Extraction with Benzo-18-Crown-6 Ether from Water into 1,2-Dichloroethane: Analyses on Ionic Strength of the Phases and their Equilibrium Potentials

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 (∆φeq) based on the Pic− transfer at the water/DCE interface were obtained from the analysis of the KD,Pic [= KD,Pic exp{−(F/RT) ∆φeq}] values; the symbol KD,Pic shows KD,Pic at ∆φeq = 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-∆φeq plot for the above Ag(I) extraction systems with Pic−, ClO4, and NO3 gave a good positive correlation.