SOLUBILITY OF A SERIESOF GASES
tial, because the looser the micellar structure, the larger the value of s. The different potentiometric behavior between DAPA and DIPA micelles may be accounted for by different micellar structure, probably the DIPA micelle having a looser structure.
1829
Acknowledgments. The authors express their thanks to Dr. H. Kita, Director of the Research Laboratories, for his encouragement and permission to publish this paper, and to Mr. T. Ohtsuka for his help in preparing the samples.
The Solubility of a Series of Gases in Cyclohexane and Dimethylsulfoxide
by J. H.Dymond Department of Chemietry, Univeredy of California, Berkeley, California O478O
(Received December IS, 1966)
An apparatus for determining the solubility of gases in liquids with enhanced speed and precision has yielded figures for the solubility in (CH3)2S0at 1 atm and 25' of He, Ne, Ar, Kr, Xe, H2, D2, N2, 02,Cot, and CH4 and for both solubility and entropy of solution in c-CsH12of Ne, Ar, Kr, Xe, H2,N2, C02, C2H8,and c-C3HB. The latter results fall closely on a straight line when the partial molal entropy of solution, & - szg (1 atm, 25") is plotted against - R In 2 2 ( 2 2 = mole fraction of the gas). The theoretical significance of these results will be discussed in a later paper by J. H. Hildebrand.
Introduction The work here reported was undertaken, first, to obtain figures of sufficient precision to serve for theoretical study of the solubility and entropy of solution of a series of gases in a single, representative, nonpolar liquid and, second, to secure data for the solubility of gases in dimethylsulfoxide, needed in connection with a study of diffusion in a liquid having high cohesion. Apparatus and Materials We designed for our purpose a new apparatus capable of more speed and accuracy than any we have used before. Its design and operation are fully described elsewhere.' Its principal features are shown in Figure 1. A bulb of -250-cc capacity, A, into which degassed solvent is introduced and accurately measured, is connected with bulb B of 100-cc capacity into which a measured amount of gas is introduced. A manometer connected at D measures the total pressure of gas plus
-
solvent vapor in B. A glass-enclosed pump in the side arm, C, operated magnetically, pumps slugs of solvent into the upper bulb, where it runs down the walls without splashing and exposes fresh surfaces of the solvent. The pressure falls to an equilibrium value from which the amount of gas that has been dissolved and hence that which would be dissolved at 1 atm partial pressure can be calculated. More gas can be added and equilibrated as a check on the attainment of equilibrium and, in the case of a very soluble gas, as a check on the applicability of Henry's law. The temperature is then changed and the system reequilibrated. The relation mole fraction of the solute) and between log $2 ( 2 2 log T is strictly linear and from the straight lines we obtain values for the partial molal entropy of solution, & - s2g(1 atm) = R(A1og x2/A log T)p. (1) J. Dymond and J. H. Hildebrand, Znd. Eng. Chem. Fundamentale, 6 , 130 (1967).
Volume 71, Number 6 May 1967
J. H. DYMOND
1830
F
Figure 2. Relation between the solubility of gases in cyclohexane at 25" and 1 atm partial pressure and their entropy of solution obtained from the linear relation R(A log z ~ / A log T )saturated at constant pressure.
Figure 1. Central part of the solubility apparatus.
The cyclohexane was Matheson Coleman and Bell Chromatoquality reagent. It was dried over Drierite and a fraction frozen out. It melted at 6.45'. The dimethylsulfoxide was Matheson Coleman and Bell Spectroquality reagent. It was dried by passing through a column of Molecular Sieve, Type 4A, and a fraction frozen out. The melting point was 18.37'. The COz was from Western Gas, Inc.; the N2 from General Dynamics Corp.; Ar from Linde Argon; Ne, Kr, Xe, and c-C3H6 from the Matheson Co.; CH, and C2H6 (Research grade) from Phillips Petroleum Co.; Dz from Bio-Rad Labs; and He, Hz, and 02 from the Stuart Oxygen Co. These gases were dried and passed directly into the apparatus.
Results The experimental figures for the mole fraction of the gases in cyclohexane saturated at 1 atm partial The Journal of Physical Chemistry
pressure and at the temperatures stated are given in Table I, together with values interpolated to 25' and entropies of solution calculated from the log z2 vs. log T slopes. Maximum deviations from these lines are less than 0.5% in 22. Henry's law was found to be obeyed even by c-C3Hsin c-CeHlzat a mole fraction of approximately 0.2. Results for the solubility of gases in dimethylsulfoxide are given in Table 11. We redetermined the figures for CF4 in C-C~HIZ in the range 17-34" and confirmed the values found by Archer and Hildebrand:2 1O4z2(25') = 10.34 and SZ sZg= 0.50; they also found for SFa 1O4zZ(25') = 53.9 and SZ - sZg = -4.9. Our value for N2, 1O4x2 (25') = 7.68, and for C02, 77.1, differ but little from the figures obtained earlier by Gjaldbaek and Hildebrand,3 7.55 and 77.2, respectively. Figures for the solubility of the rare gases in c-C6Hlz have also been determined by Clever, Battino, Saylor, and Gross4 as follows for lO'z2 (25'): He 1.21, (& - sZg= 8.1), Ne 1.80, Ar 14.9, Kr 46.7, Xe 192. In Figure 2 we (2) G. Archer and J. H. Hildebrand, J. Phys. Chern., 67,1830(1963). (3) G. C. Gjaldbaek and J. H. Hildebrand, J. Am. Chem. Soc., 71,
3147 (1949). (4) H. L. Clever, R. Battina, J. H . Saylor, and P. M. Gross, J . Phys. Chem., 61, 1078 (1957); 62, 89,375 (1958).
SOLUBILITY OF A SERIES OF GASES
1831
~~
Table I: Solubility and Entropy of Solution of Gases in Cyclohexane at 1 Atm Partial Pressure" 25.00
Ne Ar
Kr Xe H2
Nz
coz CdfS
c-C~H~ 0
19.82 1.79 17.80 15.25 20.35 48.5 19.17 228.0 20.80 4.02 17.85 7.52 20.24 80.2 19.20 258.0 15.50 1760
26.40 1.93 25.12 15.20 25.00 47.3 24.86 210.0 25.01 4.14 25.45 7.70 26.60 75.8 25.45 234.0 20.50 1550
31.60 2.04 31.05 15.20 31.60 45.7 33.00 188.5 31.62 4.34 30.70 7.87 31.08 73.1 31.20 215.0 25.00 1400
37.35 2.20 36.30 15.30 36.20 44.7 36.05 181.5 36.38 4.47 33.37 7.89 37.40 69.4 34.80 205.5 28.72 1275
1.90 15.20
61
- UP
6.8 0
47.3
-3.1
210.0
-8.2
4.14
4.2
7.68
2.0
77.1
-5.2
236.0
-8.7
1395
-14.4
The numbers on the first row are "C; the second, 104z2,where z2is the mole fraction of gas.
Table 11: Solubility of Gases, lO'z2 in Dimethylsulfoxide at 25' and 1 Atm Partial Pressure He Ne Hz
0.284 0.368 0.761
D2
Nz Ar
0.799 0.833 1.54
have plotted entropy of solution in c-cdh against the solubility as - R In zn. The open circles represent our data, the solid circles those of others referred to above plus a point for CH4 by Lannung and Gjaldbaek,6 104z2(25') = 32.7 and 32 - zsg = -2.0. This method of plotting was first used by Jolley and Hildebrand6 and since followed in subsequent papers from this laboratory. We make the following comments on the relations shown in Figure 2. (1) These results for solutions of gases in C6Hl9 are more comprehensive and reliable than those for any other solvent. We believe the values of mole fraction to be accurate to well within 1%. (2) The strictly linear relationship offers a check upon the accuracy of measurements and also a means of predicting temperature coefficients from a single determination of solubility. (3) Hz, CF4, and SFa conform rather well to this relationship, although they deviate strongly from rela-
0 2
CHI Kr
1.57 3.86 4.46
Xe C2H6
COP
17.0 17.8 90.8
tions based upon the geometric mean for the attractive potential energy of molecules of different species. (4) Since the Gibbs free energy AF = 0, the entropy of solution can be used to calculate the heat and the energy of solution. ( 5 ) Extrapolation to 2 2 = 1gives 3 2 - ~2~ (1 atm) = -20.9 cal/deg, which can be interpreted as the entropy of condensing C6H12 vapor from a hypothetical pressure of 1 atm. The entropy of condensing it from its vapor pressure at 25O, 96.6 mm, is -26.5 cal/deg. The loss in entropy in changing from 96.6 to 760 mm is 4.1 cal/ deg, giving -22.4 cal/deg. Acknowledgment. We express our appreciation to the National Science Foundation for the support of this work under a contract administered by Dr. J. H. Hildebrand. (5) A. Lannung and J. C. Gjaldbaek, Acta Chem. Scad., 14, 1124 (1960). (6) J. E. Jolly and J. H. Hildebrand, J . Am. C h m . SOC.,80, 1050 (1958).
Volume 71, Number 6 May 1067
