D. F. EVANS, J. THOMAS, J. A. ADA AS,
1714
AND
14. A.
hbkTESICH
The Conductance of Electrolytes in Acetone and in 1-Propanol-Acetone Mixtures at 25
by D. Fennel1 Evans,* John Thomas,I John A. Nadas,2 D e p r t m e n t of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106
and Sister Mary A. Matesich3 Department o j Chemistry, Ohio Dominican College, Columbus, Ohio
43919
Publication costs assisted by the Ofice of Saline Water, U . S. Department of the Interior
Conductance measurements are reported for BudKCl, EtrNBr, Pr4NBr, Bu4NBr, Et4hTI, Pr4NI, €lueNI, iilmaBuNI, Me4NC104, BuaNC104, KaBPhr, KBPh4, CsBPh4, ille4KBPh4, Bu4NBPh4, and i-Am3EEDuNBPh4 in acetone at 25" and for Bu4NC1, Bu&Br, BudNI, Bu4NC104, and LiCl in 20,40,60,80,and 90 mol acetone in 1-propanol at 25". Density, viscosity, dielectric constant, and 25-MH.z ultrasonic absorption data are also reported for the solvent mixtures. Conductance data were analyzed by the Fuoss-Onsager equation. Limiting equivalent conductance and ionic association in the solvent mixtures are compared with behavior in the two pure solvents. Walden products and association constants can be interpreted in terms of preferential anion solvation by 1-propanol through most of the composition range.
Introduction The pattern of ionic association in the two isodielectric solvents acetone and 1-propanol differs dramaticall^..^ I n acetone Bu&Cl is almost five times as extensively associated as Bu4XC1O4. I n propanol, on the other hand, the perchlorate is five times more associated than the chloride. Since the dielectric constant in the two solvents is the same, this behavior must arise from specific solvent-ion interactions. I n an effort t o obtain more information about these effects the conductance of tetrabutylainmonium chloride, bromide, iodide, and perchlorate and lithium chloride has been measured throughout the entire composition range 0-100% acetone. Before investigating the variation of K A in these mixtures, it was desirable t o obtain a complete and precise set of data for acetone, so that behavior in both pure solvents would be well established. Pistoia and Pecci have recently reported studies of the conductance of several electrolytes in acetoneethanol mixture^.^^^ They found complex behavior in the dependence of both the Walden product and the association constant upon solvent composition. However, limited solubility prevented their studying any of the electrolytes throughout, the entire composition range. Conductance measurements have also been reported in methanol-nitromethane-acetonitrile mixt u r e ~and ~ in methanol-acetonitrile mixtures.* Due to their higher dielectric constants, ionic association is much less extensive in these solvents.
Experimental Section All experimental equipment, cells, salt cup dispensing device, and general techniques for the conductance measurements were the same as those previously deThe Journal of Physical Chemistry, Vol. 76, N o . 11, 1971
scribed. 9-11 Briefly, the measurements were carried out in Kraus-type conductance cells'* and increments of salt were added t o the cell in small Pyrex cups with the aid of the Halves-Kay cup-dropping devicesg The exception to this procedure was for LiCl and BuJSCl; a weight buret was used. The tetraalliylammonium halides were purificd by recrystallization. The solvents used in recrystallization and the temperature at which the salts were dried have been given e l s e ~ h e r e .,13~ ~Tetrabutylam '~~~~ monium perchlorate was prepared by the method described by Coetzee.14 Lithium chloride (reagent grade) from a freshly opened bottle was dried under a nitrogen atmosphere in a platinum boat a t 400", ground in :in agate (1) For further details see J. Thomas, Ph.D. Thesis, Cake Western Reserve University, Jan 1970. (2) Supported by the Undergraduate Research Participation Program of the Kational Science Foundation. (3) Supported by the Research Participation for College Teachers Program of the National Science Foundation. (4) D. F. Evans and P. Gardam, J . Phys. Chem., 72, 3281 (1968). (5) G. Pistoia and G. Pecci, ibid., 74, 1450 (1970). (6) G . Pistoia, Ric. Sei., 38, 1250 (1968). (7) 11.A. Coplan and R . hI. Fuoss, J . Phys. Chem., 68, 1181 (1964). (8) F. Conti and G. Plstoia, ibid., 72, 2245 (1968). (9) J . L. Hawes and R. L. Kay, ibid., 69,2787 (1964). (10) D. F . Evans, C. Zawoyski, and R. L. Kay, ibid., 69, 3878 (1965). (11) C. G. Swain and D. F. Evans, J . Amer. Chem. Soc., 88, 388 (1966). (12) H. M . Daggett, E. J. Btiir, and C. A. Kraus, i b i d . , 73, 799 (1951). (13) R. L . Kay, C. Zawoyski, and D. F. Evans, J . Phys. Chem., 69, 4208 (1965). (14) J. F . Coetzee and G. P. Cunningham, J . Arne?. C h e w Soc., 79, 870 (1957).
CONDUCTANCE O F ELECTROLYTES IN ACETONE AND
IN
~-PROPANOL-ACETONF, AT 25"
1715
oxide for several days and then distilling from a fresh mortar, and redried in a vacuum oven at 100" ; all mabatch of calcium oxide.18 Tests for unsaturated imnipulations of this hygroscopic salt were carried out in a purities with bromine water were negative. drybox. Boride salts were prepared by metathesis of sodium tetraphenyl boride with corresponding halide The solvent mixtures employed in the conductance measurements were individually prepared in the cell salts. These salts were recrystallized five times by disjust prior to the measurements. The acetone was solving in a minimum amount, of acetone and reprecipadded from the distillation receiver in an all-glass itating by addition of peroxide free dry ether. They system. After the weight of acetone in the cell had were dried at about 50" under vacuum for several days. been determined, the propanol was added under a niConductivity grade acetone was prepared by distrogen atmosphere until the desired composition was tilling Allied Chemical reagent grade acetone from preobtained. The mixture concentrations given in the conditioned molecular sieve 3 A, 1/16-in.pellets. These tables are within 0.05%. pellets were pretreated by soaking in water for days, The density and viscosity of the solvent mixtures washing in a stream of distilled water for a day, and were determined a t 20, 40, 60, 80, 90, and 95 mol % drying first in an oven a t 140" for a month and finally in a dry nitrogen stream in a furnace at 360" for 8 hr. acetone. The density measurements were carried out The molecular sieves were stored in sealed bottles. in single-neck capillary tube pycnometers. The visThe distillations were carried out in a 1.3-m Stedman cosity measurements were made in two Cannon Ubbelcolumn and only middle fractions were retained. The ohde viscometers. The dielectric constants were meawhole process was carried out in a closed system with a sured in the all-glass platinum cells described by Kay mercury safety valve. All ground-glass joints were and Vidulich . sealed with parafilm layers. Distillations carried out Results under nitrogen gave a solvent density of 0.78433 =t The measured equivalent conductance and corre0.00002, identical with that obtained using the closed sponding electrolyte concentrations in moles per liter apsystem. Density measurements made in atmospheric pears in the microfilm edition of this volume of the conditions and in dry atmosphere did not differ. Denjournal.20 Density measurements on the most consities of 0.7845 and 0.7840 were reported by K r a ~ s ' ~ ~ ' ~ centrated solution used in the conductance measureand Hughes, l7 respectively. ment were used to obtain the volume correction necesThe results of Hughes" made it clear that extreme cauc. The density was assumed to follow sary to calculate tion should be exercised at all times to prevent contamd = do Am, where m is the moles the relationship ination of the acetone by moisture. For the conducThe solvent densities, of salt per kilogram of solution. tance runs involving pure acetone, the following proviscosities, and dielectric constants used in the evaluacedure was followed: after cleaning, the cells were tion of the conductance data are given in Table I. The dried in a vacuum oven at room temperature for sevsolvent densities were found to be linear in composition eral hours. It has been suspected that drying the cell and to be given by the relationship after cleaning causes a change in the condition of the electrodes which results in an uncertainty in the cell p = 0.79974 - 0.01544Xa,e~0ne (1) constant. The cell constant was therefore checked to better than 0.01%. These solvent properties have after drying and showed less than 0.05% variation. also been measured by Johari;21he obtained a density This was deemed preferable to the greater error that curve which displayed a slight positive deviation would result from moisture contamination of the ace(0.27%) at 50 mol%. I n Figure 1 the variation of vistone by the cell. The dried cell was flushed with argon cosity and dielectric constant with solvent composition for about 15 min and acetone was transferred directly to is shown. Our viscosity results agree very well with it from the distillation flask using an all-glass system, those of Johari, but are 30% lower than those reported The cup-dropping device was placed on the cell with dry nitrogen being flushed completely through the system. (15) M. B. Reynolds and C. A. Kraus, J . A m w . Chem. SOC.,7 0 , 1709 The exception to this careful procedure was for IJC1 and (1948). Bu4NC1. Because of their hygroscopic nature, the con(16) M. J. McDowell and C. A . Kraus, ibid., 73, 3293 (1951). ductance runs were done using a weight buret. A con(17) J. F. J. Dippy and S. R. C. Hughes, J . Chem. SOC., 953 (1954). centrated solution was made with all manipulations (18) W. C. Vosburgh, L. C. Connel, and J. A . V. Butler, ibid., 933 (1933). being carried out in a drybox. Small increments were (19) G. A. Vidulich and R. L. Kay, Rep. Sci. Instrum., 37, 1662 added from the weight buret to the cell, and in order to (1966). prevent atmospheric contamination while the cell was (20) The measured equivalent conductance and corresponding electrolyte concentrations in moles per liter will appear following these open, solvent saturated nitrogen was passed through the pages in the microfilm edition of this volume of the journal. Single side arm. The runs were made in the shortest time copies may be obtained from the Reprint Department, ACS Publioations, 1155 Sixteenth, St., N . W., Washington, D. C. 20036, by possible. referring to the author, title of article, volume, and page number. Conductivity grade 1-propanol was prepared by Remit $4.00 for photocopy or $2.00 for microfiche. drying the Fisher reagent grade alcohol over calcium (21) G. P. Johari, J . Chem. Eng. Data, 13, 541 (1968).
+
The Journal of Physical Chemistry, Vol. 76, N o . 11, 1971
D. F. EVANS, J. THOMAS, J. A. NADAS,AND 181. A. MATESICH
1716
r
I
I
I
I
I
Also given, for comparison purposes, are the corresponding values in pure propanol. I n acetone and acetone-rich mixtures the parameters obtained were found to depend upon the concentration region analyzed if K& > 0.1. Only those points below 25 x were used in the analysis. A number of duplicate conductance determinations which agree to within 0.1% in the parameters can be found in ref 1.
Table 11: Conductance Parameters for Acetone Solutions at 25”
0
20
40
100% PROPANOL
60
% ACETONE
100
80
100% A C E T O N E
Figure 1. Viscosity and dielectric constant a t 25’ as a function of mole fraction acetone in 1-propanol.
by Mocharnyuk.zz The values we obtained for the dielectric constant are consistently 0.1 unit above those determined by Johari. Also shown in Table I is the ultrasonic absorption of the mixtures at 25 MHZ. ~~
Table I : Physical Constants for Acetone-Propanol Mixtures a t 25”
a/.c
Mol % acetone
t
7
P
0 20 40 60 80 90 95 100
20.45 19.02 18.47 18.64 19.37 19.96 20.27 20.56
0.01952 0.01026 0.00647 0.00463 0.00361 0.00332 0.00316 0.00303
0.7995 0.7967 0.7936 0.7905 0.7873 0.7859 0.7861 0.7843
a
1017 26 MHza
70 47 42 38 33
30
Nepers sec-2 em-’.
The conductance data were analyzed with the Fuoss-Onsager equationz3in the form A = A. - X(Cy)l’z ECr log Cy 4( J - Bho)Cr - K4fzCy ( 2 )
+
The value of B , which corrects for the effect of the added electrolyte on the viscosity of the solvent was set equal to zero since it makes only a slight change in the 8, the ion-size parameter, and has little effect on KA. Shown in Table I1 for acetone and in Table I11 for the mixtures are the parameters obtained from eq 2 by a least-squares computer program. Where no association was detected, y was set equal to 1 and K A to zero. Included are the standard deviations in each parameter, and the standard deviations of the individual points. The .Tournu1 of Physical Chemistry, Vol. 75, KO.11, 1971
Bu4NC1 Et4NBr Pr4NBr Bu4NBr Et4NI Pr41L’I Bu~NI i-AmaBuNI MedNC104 BuaNClOi NaBPh4 KBPh4 CsBPh4 Me4NBPh4 BurNBPha i-Am3BuNBPhr LiCl
187.6 i O . l 208.8110.04 194.0 i O . l 185.34f 0.09 207.48 i 0.02 193.08 f 0.07 1 8 4 . 3 9 2 ~0 . 0 6 180.83 i 0.02 215.1 f O . l 184.75=k0.04 140.14 i 0.07 1 4 1 . 3 9 i 0.06 1 4 6 . 1 7 i 0.09 1 8 9 . 2 8 2 ~0.03 129.05 + 0.08 125.29 It 0 . 0 4 181 f 11
5.7 & O . l 5 . 2 8 i 0.07 4.8 f O . l 5.0 k O . 1 4.82 f 0 . 0 4 5.1 f O . l 5.1 1 0 . 1 5 . 1 8 f 0.07 5.3 rt0.2 5 . 7 f 0.01 6.46 f 0 . 0 7 6.73 f 0.08 4.5 f O . l 4 . 7 7 i 0.02 5.51 10.06 6 . 1 2CO.05
4 3 0 f 5 0.05 3 3 0 f 2 0.02 3 3 5 4 ~ 4 6.06 2 8 5 f 5 0.04 l 5 5 i 1 0.02 1 7 4 3 ~ 3 0.04 1 5 5 i 3 0.03 155 11 0 . 0 1 1 8 6 1 3 0.03 9 0 i 2 0.04 0.08 0.07 0.09 0.04 0.09 0.06 21 x 104 f 2 x 104
Discussion Acetone. A comparison of Table I11 with similar data given in the literature shows that the values of A. obtained in the present work are higher by about 2 conductance units. This difference can be ascribed to the lower water content of the acetone as evidenced by the low density of 0.7843 g/cc. With one exception, the densities given in the literature are 0.7845 g/cc or higher. The lowest density reported is 0.7840 g/cc; however, only the conductance of KT (A0 = 196.7 k 0.5) was rep0rted.l’ Although we did not measure the conductance of this salt, its conductance can be calculated from Table I11 by combining Ao(i-Am3BuXI) AO(I I- > Br- > C1-. Heat of transfer data reveal that chloride receives much greater additional stabilization in alcohols attributable to more effective than p e r ~ h l o r a t ea, ~result ~ hydrogen bonding to the smaller anion. This is compatible with chloride having the largest hydrodynamic radius of the anions studied, due to increased solvation. I n pure acetone, on the other hand, there is virtually no difference in the anionic mobilities. Acetone is a typical aprotic solvent in that it solvates cations strongly but anions only weakly. The mobility order for the tetrabutylammonium salts observed in pure propanol persists until the mole fraction of acetone reaches approximately 80%. This suggests that the same hydrodynamic entities present in pure propanol exist through this composition range. The salts show nearly parallel behavior in the small variations in Walden product up to 80% acetone, suggesting a common origin. The most likely explanation is a variation in the Zwanzig effect which results in a retardation in mobility at about 50% acetone. The 10% decrease in dielectric constant at this composition is in Y h e Journal of Physical Chemistry, Vol. 7 6 , N o . l l ?1971
0 Bu4NC104
0 Bu4N8r
A Bu4NI
0
V LiCl
Bu4NCI
0
F 0
