P. R. DANESI,F. SALVEMINI, G. SCIBONA, AND €3. SCUPPA
554
Behavior of Liquid Anion Membranes. Biionic Potentials NO;-Br-,
Br--CI- Couples
.Danesi, F. Salvemini, G. Scibona,” and B. Scuppa Iwivstrzal Chemistry Laboratory, C.,V.E.Y., CSS-Casaccia, Rome, Italg
(Receizled January 16, 1970)
Pztbiicatzon costs assisted by C.N.E.N., CSN-Casaccia
The membrane potentials of benzene solutioiis of nitrate, chloride, and bromide salts of tetraheptylammoniun interposed between two aqueous electrolyte solutions are reported. In the case of biionic potentials with the NO,!-.-Cl-, N08--Br-, Cl--Br- couples a quantitative correlation between the measured potential, the ionexchange coiistaiits, the ion-pair formation constants, and the ionic mobilities is discussed. The existence of a lraiisieiit potential is also analyzed and correlated to both the solubility of the alkylammonium salt in the water phase and to the ion-exchange rate (in the case of biioiiic potentials).
Introduetion The elec%roeheq-kxdproperties of low dielectric constant solutions of ‘liquid ion exchangers interposed between two :qiieous electrolyte solutions containing ions to \vl-hich 1 he organic phase is permeable have been mainly for the case of monoionic potentials. In the present papcr both monoionic and biionic potential me~sitrcmentsfor such systems (also known as liquid membrane electrodes) are reported and discussed at the light QC the current s e of the available theory wit11 the aim t o contribute to a better understanding of the potential oiiginating mechanism and then t o the design of highly selawtiveliquid membrane electrodes.
~ x ~ ~ r i~~~~~Q~ ~ e ~ t a ~
Df
I’hyyieal Chemistry, Val. 76,)Yo.
Ag, AgXILiX with M constant1
9.1 M THAX in benzene/
Reayeilk. HCI,HBr, HK03, LiBr, LiCl, and T,iNQ3 of analytical grade purity, supplied by Carlo Erba, have been u,sed in the experiments. Benzene of the same type of purrtv, supplied by Carlo Erba, has been used. Tet raheptyl ammonium iodide (THAI) supplied by Eastman Kodal; has been used to prepare the other alkylammoniinm salts. The preparation of THACl and THAIC’Qd has been already rep0rted.j THABr has been prepared- lolloning the same procedure used for THA GI. T o take into account possible concentration variations due to solubilization of the alkylammonium salt or exchange reletions (in the case of biionic potentials), ali aqireorrs and organic solutions have been analvzed by sl-andud analytical procedures before and after the membrarLepotential measurements. Silversilver chloride, silver-silver bromide, and saturated calomel electrodes have been prepared according to ref 6 and ?. Xolubzlity. The solubility of the THACl salt in EiCl solutions has teen determined by measuring potentiometrically tlie chioride concentration in the aqueous The Journal
phase before and after the equilibration of the aqueous solutions with the benzene solutions of TI-IACl (phase ratio 1:1). Interfacial Tension Measw*ements. The rneasurements have been performed following the procedure reported in ref 8. Il/lenabrane Potential Measurements. Monoionic Potentials. All the membrane potential rneasurements have been performed by using cells with stirred organic and aqueous phases unless differently indicated. I n the case of the halide ions the membrane potentials have been measured by means of the eel1
4,i97l
LiX with M variable/AgX, h g
(1)
where X- = Br- or C1-. The ernf of this cell is given by E = - RTIF In (a,’/a,”) n-here a, stands for the mean aqueous activity of the ions, “0 represents the membrane potential, and the symbols ’ and ” refer to the two aqueous sides of the cell. ]in the case of the S O 3 - anion, the membrane potential has been measured by means of the cell (1) G. Eisenman, Anal. Chem., 40, 310 (1968) (2) C. S. Coetze and H. Freiser, ibid., 40, 2071 (1968). (3) C. S. Coetze and H. Freiser, ibid., 41, 1128 (1969).
(4) (a) C. Botri! and G. Scihona, Ann. Chim.. ( R o m e ) , 5 2 , 1199 (1962); (b) J. W. Ross, Jr., Science, 155, 1378 (1967); (c) 3. W. Ross, Jr., Orion Research Inc. Bulletin 92-81. ( 5 ) P. R. Danesi, M . Magini, and 6. Scibona, “Progress in Coordination Chemistry,” Elsevier, Amsterdam, 1968, paper 6 1 9 . (6) J. Janz, “Reference Electrodes,” Academic Press. New York, N.Y., 1961, Chapter 4. (7) A. S. Brown, J . A m e r . Chem. Soc., 5 6 , 646 (1934). (8) K . Reilly and L. Rae, “Physico Chemical Methods,” T’ol. 1, Methuen, London, 1943, and bibliography therein.
555
ELECTROCHEX~CAL E~EHAVIOR OF LIQUIDANION~\IEMBRANES benzenellldcl LiC1, ddnr LiBr
gzC12,KCl(satd)/
lanr = 0.1 ;
agar-agar 0.1 Ai' LiK03/
McI/XI~ variable) ~ 1
Li?Y\p'c)3 n.ith Ad constant 1
agar-agar 0.1 11f I
