ACTIVITY OF LITHIUM IN LITHIUMAMALGAMS This indicates that the observed values of this factor differ widely from the theoretical value (h/,t)e-A8”E = 4.8 X where A is equal to h / k , as shown by Eyring, and the exponential factor has been taken to be nearly equal to 1 as AS, is a very small quantity. As given ir! Table 111, factor B’ which is very nearly equal to B, varies little within the observed range of temperature and is nearly twice Eyring’s estimated values of h N / V for the frequency factor B.
1017 The heats of activation for viscous flow of the solvent, AH,,, are found to be greater than that for dielectric
relaxation, AH,, in all of the molecules as expected. The entropies of activation for both of the processes are observed to be always negative, indicating that the activated state is more ordered than the normal state. Acknowledgments. We are deeply indebted to Dr. B. G. Gokhale, Professor Head of the Physics Department, for his continued interest and encouragement throughout the work.
The Activity of Lithium in Lithium Amalgams by David R. Cogley and James N. Butler Tyco Laboratories, Inc., Waltham, Massachusetts 02164 (Received September 8, 1967)
Activity coefficients of lithium in its amalgams have been measured using the cell Li(s)lLi+,X-lLi(Hg), where X- is C1- or Clod-, with anhydrous dimethyl sulfoxide a8 solvent. The activity coefficient (mole fraction scale, reference state infinite dilution) is given by the relation, log y ~ = i (14.6 0.4)X~i, for XLi < 0.013 (saturation), and the solutions appear to be regular within experimental error. The standard potential difference between the solid lithium and lithium amalgam electrodes is 0.8438 f: 0.0002 V. A saturated amalgam at 25’ contains 1.33 mole % lithium.
Introduction I n the course of our studies on the kinetics of the lithium amalgam-lithium ion electrode in nonaqeuous solvents,‘ we have measured the activity coefficient of lithium in its amalgams a t room temperature, as well as the potential difference between the amalgams and solid lithium. The potential difference between a lithium amalgam (1.00 mole %) and solid lithium electrode in a propylamine-lithium iodide electrolyte was measured by Lewis and Keyes2 as part of their determination of the standard potential of the lithium electrode in aqueous solutions. Since they used the same amalgam composition for the aqueous cell, it was unnecessary for their purpose to determine the activity coefficient of lithium in the amalgam, and they made measurements with onlly one amalgam composition. Spiegel and Ulichs measured the potential difference between various lithium amalgams ranging in composition from 0.03 to 2.3 mole yo,using electrolytes consisting of LiCl dissolved in acetone, methanol, or acetonitrile, but the potential with respect to solid lithium was not measured. Although the activity coefficients obtained in the different electrolytes were consistent within experimental error, the dependence of activity coeffi-
cient on amalgam concentration showed strong deviations from regular solution behavior. Both sodium and potassium amalgams appear to be regular in this concentration range.4 I n view of these discrepancies, we decided to redetermine the potential between lithium and its amalgams and the activity coefficients of the amalgams, using dimethyl sulfoxide (DMSO) as a solvent. A high degree of reversibility and stability of the lithium amalgam’ and lithium electrodes5 has been demonstrated in LiC1-DMSO solutions.
Experimental Section Lithium amalgams were prepared from triple-distilled mercury (Doe and Ingalls), which had been freed of oxygen by passing it through a porous frit in an argon atmosphere, and lithium ribbon (Foote Mineral Co., (1) D . R. Cogley and J. N. Butler, J. Electrochem. SOC.,113, 1074 (1966). (2) G . N . Lewis and F. G. Keyes, J . A m . Chem. Soc., 35, 340 (1913). (3) G. Spiegel and H. Ulich, Z.Physik. Chem., A178, 187 (1937). (4) M . 0. Davies, et al., “The Physical and Chemical Properties of Dilute Alkali Metal Amalgams,” Technical Reports No. 7 (June 1957) and 20 (July 1963), Contract Nonr 581(00). Part I : AD 138 849; part 11: AD 609 294. (5) W. H. Smyrl and C. W. Tobias, J . Electrochem. SOC.,115, 33 (1968).
Volume 72, Number 3 March 1968
DAVIDR. COGLEY AND JAMES N. BUTLER
1018 99.97%) by combining weighed quantities of the two materials or by dilution of a more concentrated amalgam with mercury. The amalgams were analyzed by decomposition with aqueous acid and analysis of the resulting solution for Lif by flame photometry. The flame photometer (Instrumentation Laboratories Model 143-A) was calibrated with solutions of approximately the same composition in Li+ and exactly the same internal standard concentration (1 mMK+) as the samples to be analyzed. The difference between duplicate analyses was always less than 1%, and often as small as 0.1%. The analysis agreed with the composition as prepared within experimental error. Electrolytes were prepared from anhydrous LiCl or LiC104 (Anderson Physics Laboratories, ultrapure grade) and anhydrous dimethyl sulfoxide (Rfatheson Coleman and Bell, Chromatographic grade). The solvent was treated for 1 week with Linde 5A Molecular Sieve (which had been dried for 16 hr at 500" in argon) to remove the last traces of water. To avoid contamination by any solid particles from the molecular sieve, the treated solvent was filtered through a 10-20-11 glass frit. The water content of the solutions was less than O.OOl%, as determined by gas chromatography6 on a column of Porapak Q (Waters Associates). No organic impurities could be detected, and it is estimated that their concentration was less than 0.005%. Potentials were measured with a high-impedance differential voltmeter (John Fluke), which was calibrated against a Weston standard cell (Eppley Laboratories) and found to be accurate to f0.05 mV. Potentials were normally read to the nearest 0.1 mV. All manipulations were carried out in an argon atmosphere containing less than 1 ppm of water, oxygen, or nitrogen (Vacuum Atmospheres Corp. drybox) and at ambient temperature. The temperature was measured to within 0.03" and was 25 f 1" for all experiments.
Results We measured the potential of 39 cells of the type
perature, F is the Faraday constant, XLiis the mole fraction of lithium in the amalgam, and y ~ isi the activity coefficient of lithium in the amalgam. If the electrode
Table I : Experimental Results XLi
x
10'
where E O L ~ ( H is ~ )the standard potential of the lithium amalgam (reference state: infinite dilution, mole fraction scale), E " L is ~ the standard potential of solid lithium, R is the gas constant, T is the absolute temThe Journal of Physical Chemistry
E, V
LO?
Ya
Series 1A: 1 M LiC104 in 24.65 0.9454 24.68 0.9655 24.68 0.9912 24.70 1.0170 24.71 1.0358 24.72 1.0625 24.72 1.0888 24.73 1.1229
DMSO
127.6 70.43 28.90 11.33 5.538 I.996 0.720 0.025
Series 1B: 1 M LiC104 in 24.55 0.9450 24.57 0.9657 24.58 0,9914 24.60 1.0172 24.61 1.0360 24.63 1.0627 24 64 1.0891 24.65 1.1237
DhtSO
127.6 70.43 28.90 11.33 5.538 1.996 0.720 0.205 127.6 70.43 28.90 11.33 5.538 1.996 0.720 0.205
YLi
14.091 14.172 14.221 14.250 14.258 14.266 14.268 14.300 14.084 14.176 14.226 14.255 14.262 14.271 14.274 14.315
Series 1C: 0 . 1 M LiC104 in DMSO 24.50 0,9451 14.086 24.51 0.9653 14.170 14.219 24.52 0.9910 14.248 24.52 1.0168 1 0357 14.258 24.53 1.0623 14.265 24.53 1.0887 14,269 24.54 1.1228 14.301 24.55
0.178 0,097 0,048 0.019 0.011 0.003 0.001
... 0.190 0.098 0.048 0.019 0.012 0.003 0.000
...
0.183 0,099 0.050 0.021 0,011 0.004 0.000
...
1 M LiCl in DMSO 0.9430 14.061 0.9431 14.062 0.9478 14.092 0,9743 14.182 1.0908 14,245
0.208 0.207 0.177 0.087 0.0249
86.57 52.25 29.31 0.66
Series 2B : 0 . 2 M LiCl in DMSO 26.0 0,9588 14,141 26.0 0.9745 14.187 25.9 0.9912 14.218 26.0 1,0908 14.248
0.128 0.082 0,051 0.0211
133. 2c 118.8 86.57 52.25 29.31 0.66
Series 2C : 0 . 2 M LiCl in DMSO 25.3 0.9434 14.072 25.5 0.9478 14.096 25.7 0,9587 14,141 25.2 0.9743 14.188 25.8 0.9912 14.218 25.6 1.0912 14.260
0.197 0.173 0.128 0,081 0.051 0.0099
133,2c 133. 2c 118.8 52.25 0.66
Li(s)lLi+, X-, DMSOILi(Hg) (where X- is either C1- or C104-) as a function of amalgam concentration from 0.002 to 1.33 mole % Li. The concentrations and potentials are summarized in Table I. The potential of the cell is given by the expression R?' E = E o L i ( H g ) - E'L, - - In (XLiyLi) (1) F
T, O C
Series 2A: 26.1 26.2 26.2 26.2 26.2
'
Corrected to a Corrected to 25" using AH" = -19.8 kcal. 25'. Calculated using AE" = 0.8440 V except for series l B , Saturated amalgam, over-all comwhere AE" = 0.8443 V. = 0.01394. position X L ~
(6) R . J. Jasinski and S . Kirkland, Anal. Chem., 39, 1663 (1967).
ACTIVITY OF LI'IHIUM IN LITHIUM AMALGAMS
142lb
I
,001
XL,
I ,002
1019
I
,003
Figure 1.
reactions are ideally reversible and no side reactions take place, the potential of the cell is independent of electrolyte composition. All of the measurable parameters were combined into the function
F Y = 2.303RTE
AH" + log XLi + 2.303R(k -- - 2k3)
Figure 2.
(2)
represents the constant potential of a saturated amalwhich is listed in Table I. The last term is a small gam. The point of intersection is the concentration of correction for the temperature variations, and for this lithium in the saturated liquid phase: X L = ~ 0.0133. we used the standard enthalpy of the r e a ~ t i o n ~ . ~ Discussion Li(s) Hg = Li(Hg) (AH" = - 19.8 kcal/mole). The results of our measurements are compared with Extrapolation of the function Y to X L ~ = 0 gives the standard potential difference AE" = E " L ~ ( H-~ ) those of previous workers in Figure 2. Although the data of Spiegel and Ulicha agree with our results at E O L i ; and eq 1 can then be used to calculate an activity X L
