2336
R. KAY,T. VITUCCIO,C. ZAWOYSKI,AND D. EVANS
Viscosity B Coefficients for the Tetraalkylammonium Halides
by Robert L. Kay, T. Vituccio, C. Zawoyski, and D. F. Evans' Mellon Institute, Pittsburgh, Pennsylvania
16g16 (Received February 8, 1966)
Viscosity measurements a t concentrations up to 0.2 M for the tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutylammonium bromides and iodides are reported in H20, D20, CHaOH, and CHICN a t various temperatures between 0 and 65". The viscosity B coefficients calculated from the Jones-Dole equation exhibit the same behavior as would be predicted from the dependence of the Walden product on solvent and on temperature. In aqueous solutions, the Pr4N+ and Bu4N+ ions appear to be excellent structure makers and the Me4N+ ion appears to be a structure breaker, while for the Et4N+ ion the two effects appear to cancel.
Introduction I n the preceding paper,2 the Walden product for spherical ions in aqueous solution was shown to be influenced by solvent structural effects. Gurney3 has shown that there is a relationship between the temperature coefficients of the Walden product and viscosity B coefficients obtained from the Jones-Dole4 equation for the alkali halides in aqueous solution. Here we report viscosity B coefficients for the tetraalkylammonium bromides and iodides and show that a similar relationship exists for these large symmetrical ions depending on the specific structure-making or structure-breaking ability of the ions involved. Temperature dependence of the B coefficients have been measured in H20, D20, methanol, and acetonitrile solutions to illustrate clearly the dependence of transport properties on the amount and type of structure in the solvent. These B coefficients have been usedalready to correct the concentration dependence of conductance for the viscosity effect of these large cation^.^
for all of the solutions at 65" were assumed to be identical with those at 45". Two Ubbelohde-type suspended-level viscometers with flow times for water at 25" of 500 sec were employed in all of the measurements. One of the viscometer# was found to give the same calibration for a number of nonaqueous liquids of low surface tension, whereas the other was constructed here and gave accurate results for aqueous solvents. Neither viscometer was found to require a kinetic energy correction based on the results of repeated runs on a number of concentrated sugar solutions. Runs were repeated until three determinations within 0.2 sec were obtained.
Results The relative change in viscosity, I,due to the addition of salt to the solvent, was obtained from the measured flow times, t and to, for solutions and solvent, respectively, by means of
-
#E--= 3 70
Experimental Section The purification of all materials used as well as procedures in preparing solutions have been discussed in detail already.6 All viscosity measurements were carried out in a constant-temperature bath controlled to within 0.02" of the stated temperature with the absolute temperature determined by a calibrated platinum resistance thermometer. All solutions were prepared on a weight basis and vacuum and density corrected. For this purpose, the density increments The Journal of Physical Chemistry
70
p(t
- At) - pot0 PO6
(1)
(1) Chemistry Department, Western Reserve University, Cleveland, Ohio 44106. (2) R. L. Kay and D. F. Evans, J . Phys. Chem., 70, 2325 (1966). (3) R. W. Gurney, "Ionic Processes in Solution," McGraw-Hill Book Co., Inc., New York, N. Y., 1953, p 170. (4) G. Jones and M. Dole, J . Am. C h m . SOC.,51, 2950 (1929). (5) R. L. Kay and D. F. Evans (a) J. Phgs. Chem., 69, 3878, 4208 (1965); 70, 366 (1966); (b) ibid., 69, 4216 (1965). (6) Cannon Instrument Co., State College, Pa.
2337
VISCOSITY B COEFFICIENTS FOR TETRAALKYLAMMONIUM HALIDES
This can be written as
Table I: Viscosity Data for the Tetraalkylammonium Halides between c) and 65"
low
!b/c'/2
102c
-HzO, Bu4NBr 0.80 0.16 1.97 0.244 3.96 0.343 4.36 0.360
0"
------HzO, Pr4NBr 0.99 0.100 4.91 0.213 9.73 0.307 14.44 0.384 19.01 0.463 Et4NBr 0.99 0.037 11.94 0.139 Pr4NI 1.08 0.095 5.07 0.201 9.70 0.285 14.46 0.363 18.94 0.423
10"-
!b/cl/2
BunNI 3.95 0.333
Bu4NBr 0.42 0.108 1.09 0.160 1.81 0.202 2.98 0.258 3.98 0.300 5.19 0.343 Me4NBr 15.89 0.029 Bu~NI 0.50 0.109 0.99 0.144 1.39 0.172 2.86 0.246 3.93 0.289
Hz0, 25"-Pr4NBr Pr4NI 0.99 0.085 0.50 0.064 1.08 0.081 4.90 0.182 5.06 0.170 9.70 0.256 9.67 0.242 14.39 0.315 14.42 0.297 18.95 0.373 Bu4NBr 18.88 0.351 1.81 0.178 B u.4NI 0.50 0.120 2.98 0.220 0.99 0.117 3.97 0.250 1.39 0.142 5.18 0.291 MerNBr 2.85 0.206 3.92 0.244 15.84 0.040 -HzO, Bu4NBr 1.25 0.145 2.22 0.167 4.81 0.226 8.90 0.304 Et4NBr 8.07 0.092 15.78 0.131
l o w */c'/e
Pr4NBr 2.44 0.108 4.18 0.139 9.94 0.212 18.73 0.302 Me4NBr 17.73 0.051 25.75 0.063 Me4NBr 16.63 0.052 32.00 0.070 34.92 0.074
Et4NBr .4.02 0.059 10.57 0.096
102c
!b/c'/n
DzO, 10"Bu4NBr 1.33 0.188 2.75 0.268 5.12 0.359 Pr4NBr 0.90 0.117 3.97 0.204 Pr4NI 4.00 0.191
Bu~NI 0.90 0.149 1.58 0.192 4.15 0.310 Me4NBr 0.89 0.013 9.85 0.021
me4n1 9.98
Dz0, 25"-
0.005
-
Bu4NBr 1.33 0.155 2.75 0.228 5.12 0.294 Pr4NI 3.99 0.160 Bu~NI 3.94 0.250
Pr4NBr 0.89 0.091 3.96 0.169 Me4NBr 0.89 0.010 9.84 0.029
-CH30H, Bu4NBr 0.65 0.096 2.58 0.163 4.93 0.213 15.56 0.371
10"Bu~NI 1.79 0.131 7.03 0.237 Me4NBr 6.68 0.105
-CHIOH, Bu4NBr 0.31 0.079 0.64 0.094 2.54 0.158 4.84 0.205 15.31 0.354 Bu~NI 1.76 0.127 6.91 0.226
25"Me4NBr 3.12 0.078 6.57 0.105 19.32 0.169 Et4NBr 6.64 0.145 11.62 0.181 12.42 0.185 Pr4NBr 6.05 0.181 12.50 0.253
-CHsOH, Bu4NBr 5.27 0.220 10.46 0.299 Pr4NBr 5.93 0.180 11.56 0.249
45"Et4NBr 6.49 0.149 11.35 0.189 12.13 0.192
-CH,CN, Bu4NBr 0.79 0.089 2.84 0.153 4.90 0.195
10"Bu~NI 4.95 0.195
-CHsCN, Bu4NBr 0.78 0.087 2.78 0.143 4.80 0.180
25"-
46"-
Hz0, 65"BuaNBr 3.76 0.173 7.24 0.229 10.21 0.268 14.97 0.333 Pr4NBr 5.85 0.138 14.62 0.214
rl, =
me4n1 9.97
0.290
Bu~NI 4.85 0.183
\LM -
pAt/poto
(2)
where At is a flow time correction found necessary for some of the salts studied in aqueous solution and was detected by the fact that r l , ~did not extrapolate to zero as C --t 0. The magnitude of At was determined by measuring the viscosity of solutions so dilute (C < 10-6 M ) that the flow time should have been that of the pure solvent. The maximum difference in time encountered amounted to 2 sec. The At determined in this way were found to give rl, that extrapolated to zero as C --t 0 in every case where the correction was required. This correction was required for only three sets of data, Bu4NI, Pr4NBr, and Pr4N1, in aqueous solutions. The fact that At was detectable in such extremely dilute solutions suggests that it is a surface tension effect resulting from a minute trace of surfaceactive impurity in the salts in question. We have detected this same behavior in the data for Bu4NBr reported by other workers.' The values of rl,/C'/2 in Table I for all systems studied have been corrected where necessary. The solution densities used in eq 1 were obtained by direct measurement generally on the most concentrated solution studied. It was found that the relationship d = do B f i , where f i is the concentration in moles per kilogram of solution, held over a wide concentration and temperature range. Consequently, many of the required values of 0 could be estimated from values obtained by direct measurement. The viscosity B coefficients in Table I1 were obtained empirically from the Jones-Dole4 equation
+
rl,/C'/z = A
+ BC'/?
(3) The validity of the relationship was established for each of the solvent systems investigated and for the temperature range studied by measuring at least one salt containing the larger ions at a number of points covering a wide concentration range. Once this was established, only one or two points were required to obtain B coefficients for other salts. Included in Table I1 are the data of Laurence and Wolfendens for EtrNBr and the data of Huckel and Schaaf9 for Et4NI and Me4NIin aqueous solutions. The intercepts A on a plot of eq 3 were small in every case and contributed very little to the concentration (7) R. M. Fuoss and C . A. Kraus, J . Am. Chem. SOC.,79, 3304 (1957). (8) V. 0.Laurence and J. H. Wolfenden, J . Chem. Soc., 1144 (1934). (9) E. Htickel and H. Schaaf, 2. Physik. Chem., 21, 326 (1959). The values of B for 10" were extrapolated from data a t somewhat higher temperatures.
Volume 70,Number 7 July 1966
R. KAY,T. VITUCCIO, C. ZAWOYSICI,AND D. EVANS
2338
Table 11: Viscosity B Values at Various Temperatures t,
“C
MerNBr
EhNBr
PrrNBr
BudNBr
65 45 25 10 0
0.11 0.10 0.083 0.058
0.27 0.30 0.34” 0.38
0.54 0.64 0.82 0.98
0.83 0.99 1.24 1.46 1.68
25 10
0.076 0.049
0.79 0.94
1.26 1.56
0.67 0.66
CHsOH 0.86 0.85 0.89
0.80 0.82
CHsCN 0.74 0.80
0.75 0.80
MaNI
ECNI
PrrNI
BurNI
0. 049’ 0. O2Sb
0.31‘ 0.33b
0.77 0.93
1.19 1.41 1.61
0.74 0.88
1.21 1.48
Hz0
D20
45 25 10
0.35 0.35
25 10
“ See ref 8.
0.50 0.48
0.034 0.00
’See ref 9.
dependence of viscosity with the possible exception of the aqueous tetramethylammonium salts. At most A amounted to 0.01 in aqueous and 0.02 in nonaqueous solutions. This term in the viscosity equation is interpreted as the contribution from interionic forces that tend to interfere with the flow of one layer of solution past another. Theoretical values calculated from the Falkenhagen equationlo agreed within 25% with the measured values. Plots of eq 3 were found to be linear up to concentrations of 0.1 M in aqueous solution and to somewhat higher concentrations in methanol. In aqueous solution, positive deviations were observed at higher concentration of the larger salts and introduced some uncertainty in the determination of B. The internal consistency of our results is shown in Table I11 by the constant difference in B for bromides and iodides in HzO and DzO solution. Our value of 0.05 compares well with the generally accepted value of 0.03 for aqueous solutions.” Furthermore, the difference between our MerNBr and Huckel and Schaaf’s values for Rfe4NI is 0.03 over the whole temperature range as can be seen in Figure 1, although the agreement between Et4NBr and Et4NI is not as good at temperatures above 25”. Our values for Et,NBr a t higher and lower temperatures are consistent with that of Laurence and Wolfenden at 25”, as is also shown in Figure 1. Kaminskyl2 has demonstrated the additivity of ionic B coefficients for aqueous solutions at various temperatures. The Journal of Physical Chemistry
Table III: Value.3 of (BBT- BI-) t,
BurN +
PnN
Hz0
10 25
0.05 0.05
0.05 0.05
DzO
10 25
0.08 0.05
0.06 0.05
O C
+
MerN
+
0.05 0.04
A plot of our B values for the bromides in water and methanol solutions at the various temperatures studied is given in Figure 2. Although WenW3 values for Bu4NBr in water are somewhat lower, the temperature dependence is in good agreement with our own. The value of 1.34 quoted by Fuoss and Kraus’ reduces to 1.27 if the high points at the two lowest concentrations reported are corrected for At as mentioned above. This value is in good agreement with our value of 1.24 quoted in Table 11. nightingale'^'^ B value for Me4NBr is in good agreement with our data only at (10) H. Harned and B. B. Owen, “The Physical Chemistry of Electrolytic Solutions,” 3rd ed, Reinhold Publishing Corp., New York, N. Y., 1958,p 240. (11) R. H. Stokes end R. Mills, “Viscosity of Electrolytes and Related Properties,” Pergamon Press Inc., New York, N. Y . . 1965, p 34. (12) M. Kaminsky, Di8CU88wnS Faraday Soc., 24, 171 (1957). (13) W. Y.Wen, Ph.D. Thesis, University of Pittsburgh, 1957. (14) E.R. Nightingale, Jr., J . Phys. Chem.,66, 894 (1962).
VISCOSITYB COEFFICIENTB FOR TETRAALKYLAMMONIUM HALIDES
'
-0.21
IO
I
1
I
1
1
20
30
40
50
60
T'C Figure 1. The temperature dependence of viscosity B coefficients for aqueous solution: EtdNBr: 0, our data; 8 , see Laurence and Wolfenden, ref 8; Et4NI and Me4NI, see Huckel and Schaaf, ref 9; MeaNBr, our data; I-, see Kaminsky, ref 12.
2339
the smaller ions from 12.5 to 45". He justified this split on the basis of the almost identical cation and anion transference numbers for KC1 at all temperatures and by the fact that he obtained ionic values in good agreement with those reported by Cox and Wolfenden15 that were based on the mobility difference for the Li+ and IO3- ions. We have followed Kaminsky's procedure and have used his data for the iodide ion shown in Figure 1 and the difference ( B Y ~ ~ N B ~ - BH~,NI), also shown in Figure 1, to calculate B B ~ and consequently all of the ionic B coefficients for the tetraalkylammonium ions given in Table IV. A similar split cannot be used to obtain ionic B values for methanol and acetonitrile solutions because of the lack of suitable data for KC1 and KBr in these solvents. Viscosities of dilute methanol solutions of KCl and KBr as determined by Jones and FornwalP produced two values of B, depending on the concentration range considered, whereas our data for the quaternary salts gave very linear plots of eq 3 and a single value of B over the same concentration range. Ionic B values for methanol solutions will require a reinvestigation of at least KC1 in methanol solutions.
I
70
Tabie IV: Ionic B Values a t Various Temperatures in HzO t,
OC
BUN+
Pr4N+
EtrN+
MedN+
Br -
0
1.75 1.52 1.28 1.01 0.84
1.04 0.86 0.66
0.44 0.38 0.32 0.28
0.13 0.12 0.12 0.12
-0.07
10 25 45
65
-
Q t
c
v
*
I1
v
I
I
I
To, Figure 2. Viscosity B coefficients for the tetraalkylammonium bromides in water and methanol solutions as a function of temperature: @, Fuoss and Kraus, ref 7; C), Wen, ref 13; 0, Xightingale, ref 14.
-0.08
0.55
-0.04 -0.02 -0.01
Our data for Me4NBr and Bu4NBr in CH30H at 25" are in acceptable agreement with the values 0.42 and 0.84, respectively, quoted by Tuan and F U O S S , ~ ~ but our values for Bu4NBr and Bu4NI in CH,CN are consistently lower than their values of 0.93 and 0.87, respectively.
Discussion
2oo
since his temperature dependence differs significantly from ours and from that reported by Huckel and Schaafs for Me4NI (see Figure 1). _A_ satisfactorv discussion of the temDerature dependente Of coefficients requires the ionic rather than salt values. Unfortunately, there is no exact method of performing this operation since the equivalents of transference numbers do not exist for viscosity data. Kaminsky12assumed that B K += Bcl- a t all temperatures and calculated ionic B values for a number of
Viscosity B coefficients from the Jones-Dole equation Can be interpreted, at least qualitatively, by the Einstein
(15) W. M. Cox and J. H. Wolfenden, Proc. Roy. SOC. (London), ~145,475(1934). (16) G. Jones and H. J. Fornwalt, J. Am. Chem. SOC.,57, 2041 (1935). (17) D. F.-T. Tuan and R. hl. Fuoss, J . Phys. Chem., 67, 1343 (1963). (18) A. Einstein, Ann. phg8ik, 19,289(1906); 34,591 (1911).
Volume 70,Number 7 July 1966
R. KAY,T. VITUCCIO,C. ZAWOYSKI, AND D. EVANS
2340
for aqueous solutions, whereas the values are about constant for methanol solutions. These effects must where v is the total volume occupied by the ions per be due to the large R&+ ions since the contribution milliliter of solution. This equation predicts that the to the B values from the bromide ion is very small, presence of ions should increase the solution viscosity as can be seen in the ionic values in Table IV. Corin proportion to their size, and the increase should be responding behavior has been observed in the Walden independent of temperature inasmuch as electrostrictive product for these ions.2 Thus, the viscosity data consolvation is independent of temperature. B coeffifirm the conclusions reached from the conductance cients for the relatively small alkali and halide ions in data that water enforcement about the hydrocarbon aqueous solution have been shown to deviate considerside chains of the Pr4N+and Bu4N+ions forms a larger ably from this behavior. The B values decrease with moving entity and, at the same time, increases the bulk increasing ion size, often to negative values,3,11 and in viscosity by increasing the degree of hydrogen bonding such cases B increases with increased t e m p e r a t ~ r e . ' ~ ~ ' ~ *in' ~their vicinity. This interpretation is in agreement This is in the opposite direction for hydration effects, with all known data for these ions as was pointed out and, consequently, this behavior has been attributed to in the preceding paper. the ability of these ions to disrupt water structure in The B values for Me4NBr show a much different betheir v i ~ i n i t y . ~These , ~ ~ ions have become known havior. They are much smaller in aqueous than in as structure breakers, and the same explanation has methanol solution at all temperatures, and they show been used to account for the Walden product and its a slight increase with increasing temperature. This temperature dependence.2 As a matter of fact, it has temperature dependence, however, is most likely due been s h o ~ n ~that, z ~ ~owing to this dependence on entirely to the Br- ion, as can be seen from the data in water structure, B and the X O product ~ for structureTable IV. These results indicate that, if the B CObreaking ions are related reciprocally in that, if B is efficient for the Me4N+ ion has any temperature delow, is high, and, if B increases with temperature, pendence, it is small. This result is in agreement with Xov decreases with increasing temperature. that found by Huckel and Schaffg from more precise No previous systematic stJudyas is reported here has data on &!fe4NI. The true temperature dependence been carried out for B coefficients of the tetraalkylamhere is difficult to determine because of the arbitrary monium ions. Frank and Evans have used Bingham'sZ1 nature of the split used to obtain ionic values. The A values (the viscosity increase for a 1 m solution) to Walden product for this ion was found2 to be higher in illustrate the relatively large increase in viscosity obaqueous than in methanol solutions and to decrease tained in aqueous solutions of these ions and have with increasing temperature. At least in its behavior attributed this excess viscosity to "iceberg" formation. in aqueous as opposed to nonaqueous solvents, these However, in light of the Einstein equation, the measviscosity data confirm the structure-breaking properured viscosity could be attributed to the increased size ties of the i\4e4N+ion. of the tetraalkylammonium ions. Better criteria for The Et4N+ ion shows a mixed behavior since B for structure influences can be obtained from the temperaEt4NBr is slightly lower in aqueous than in methanol ture dependence of the B coefficients. Huckel and solution but still shows a small decrease with increased Schaafg have investigated the temperature dependence temperature in aqueous solution. Both effects are too of only the smaller of these ions. Wen's datal3 for large to be accounted for by the bromide ion alone. Bu4n'Br at 20 and 30" in aqueous solution illustrates Huckel and Schaafe have come to the same conclusion the large negative temperature dependence of B COfor the Et4N+ion from their studies of aqueous Et4NI. efficients for the larger quaternary ammonium ions. The Walden product2 for this ion is lower in water It is evidence such as this, when combined with data than in methanol and shows little temperature defor nonaqueous solvents, that permits conclusions to pendence. Both the viscosity and conductance data be reached concerning the effects of ions on solvent can best be interpreted by assuming this ion is of an structure. intermediate size for which structure-making and structure-breaking effects cancel. The same type of relationship between B and XO? is Further evidence for the conclusions reached here is found here for the large quaternary ammonium ions contained in the B values for DzO solutions. They are in aqueous solution as was found for the alkali halides. I n Figure 2 it can be seen that, a t low temperatures, B for Bu4NBr and Pr4NBr in aqueous solution are (19) J. D. Bernal and R. H. Fowler, J . Chem. Phys., 1 , 515 (1933). larger than the corresponding values in methanol (20) H. S. Frank and hI. W. Evans, ibid., 13, 507 (1945). solutions and B decreases with increased temperature (21) E. C. Bingham, J . Phys. Chem., 45, 885 (1941).
B = 2.5v/c
The Journal of Physical Chemistry
(4)
2341
THERMAL DIFFUSION IN THE Bi-BiIs SYSTEM
almost identical Yith those for HzO solutions. We had hoped to verify the increase in structure-making properties of the large hydrophobic cations, Bu4N+ and Pr4N+, in DzO over that in HzO as was demonstrated from conductance measurement^.^^ Although the trends are in the expected direction, the effect is too small to be established by viscosity measurements with the precision reported here. It is interesting to calculate B coefficients from eq 4 using data reported by Robinson and Stokes22 for the ionic radii. The results are given in Table V and indicate a surprisingly good agreement with the observed data for these salts in methanol solutions. However, considering the assumptions involved in the model used and the general lack of data for nonaqueous
solvents, this agreement must be considered fortuitous a t the present time. Table V: Viscosity B Values Calculated from Eq 4 MerNBr
EtrNBr
PrlNBr
ButNBr
Br -
0.31
0.45
0.63
0.81
0.05
Acknowledgment. This work was supported by Contract No. 14-01-0001-359 with the Office of Saline Water, U. S. Department of the Interior. ~~
~
~~
(22) R. A. Robinson and R. H. Stokes, "Electrolyte Solutions," Butterworth Inc., New York, N. Y., 1959.
Thermal Diffusion in an Oxidation-Reduction Thermocell-the Bismuth-Bismuth Iodide System1
by Jordan D. Kellner Atomics International, A Division of North American Aviation, Inc., Canoga Park, California (Received January 4 , 1966)
The Soret effect was studied in a metal-fused salt system by measuring the final thermoelectric potential (in the Soret steady state) of a Bi-BiI, thermocell, containing inert electrodes, over the composition range 1-90 mole % bismuth. The value at 500" was large a t low metal concentrations (-4600 pv/deg at 1 mole % metal) and diminished exponentially to that of the initial thermoelectric power at about 30% dissolved bismuth metal. From 30 to 90% bismuth, the initial and final thermoelectric powers were identical. No Soret effect is observed at compositions where electronic conduction predominates. At these compositions the results suggest that the transport properties of the cations (Bi+, Bi3+) are indistinguishable because the electron exchange between cations is much faster than ionic migration.
Introduction The Soret effect occurs when a temperature gradient is imposed on a two-component liquid system. A partial demixing results which continues until a steady state is reached where the diffusion along the tempera-
ture gradient is just balanced by ordinary diffusion in the opposite direction along the concentration gradient. (1) This work was supported by the Research Division of the U. 9. Atomlc Energy Commission.
Volunw 70, Number 7 July 1966
