Potentiometric study of liquid membrane transports of ionic Na(I) species with some crown ethers into nitrobenzene and 1,2-dichloroethane

Abstract

Potentiometric measurements of the following liquid-membrane-transport cell were performed at 298 K. Cell: (−) Ag|AgCl | 0.05mol dm −3 (C 5 H 11 ) 4 N + Cl − ¦ nitrobenzene (NB) or 1,2-dichloroethane (DCE) ¦* 0.05mol dm −3 NaCl with L, NaOH, and picric acid | AgCl|Ag (+), where the symbols ¦ and L denote an interface with a sintered glass and a crown ether, respectively. 15-Crown-5 ether (15C5), benzo-15C5, 18-crown-6 one (18C6), and benzo-18C6 were used as L. Assuming emf={distribution equilibrium potentials (Δϕ eq /V) around the NB/-or DCE/water interface expressed by the asterisk} + other potentials in the cell, the relation of (F/RT)emf ≈ kt + ln K D ′ was derived under the conditions of K D >>1 and a steady state. Here, emf, k, t, K D and K D ′ refer to an emf (mV) measured between the two Ag/AgCl electrodes, an apparent first-order-reaction rate constant (minute −1 ) for the distribution of Na(I) species, a monitored time (minute), a conditional distribution constant of the Na(I) species into the NB or DCE phase, and its modified K D , respectively. With the Δϕ eq values previously-reported at 298K, positive correlations of the ln K D ′ values obtained from the (F/ RT)emf-vs.-t plots were observed in the systems with the four L employed; their correlation coefficients obtained from Δϕ eq -vs.-ln K D ′ plots were 0.909 for the NB system and 0.896 for DCE. These good correlations indirectly confirmed the presence of Δϕ eq for the liquidmembrane transport systems. The emf values of another cell was also analyzed.