84
BENTONB. OWENAND PAULL. KRONICK
Vol. 65
The entropies of formation of liquid plutonium chloride a t 700' was determined to be -170 (111) chloride in the various solutions are estimated kcal. which is 4a/, more positive than that estimated to be reproducible within 8%. A source of uncer- by L. Brewer, L. Bromley, P. W. Gilles and If. L. tainty in the calculation of the free energy of forma- Lofgren.2 tion of pure plutonium(II1) chloride stems from Acknowledgments.-I wish to thank J. A. the extrapolation of the data for the solutions a t Learv and R. D. Baker of the Los Alamos Scientific 700' to the state of pure supercooled liquid pluto- LabGratory and Milton Kahn of the University of nium(II1) chloride. The extrapolation involves a New Mexico for discussions and encouraging interrelatively small correction, uiz., 0.5%. ests. I am indebted to A. N. Morgan for the Discussion.-The relative partial molar free plutonium, J. W. Anderson for the machined pluenergy of mixing the plutonium(II1) chloride has tonium electrodes, C. F. Metz, G. R. Waterbury, large negative values which is consistent with the C. T. Ape1 and A. Pullium for chemical analyses, compound formation observed in the study of and S. D. Stoddard for the thoria crucibles. This phase equilibria. The value of the standard molar work was done under the auspices of the U. S. free energy of formation of pure plutonium(II1) Atomic Energy Commission.
STANDARD PARTIAL MOLAL COMPRESSIBILITIES BY ULTRASONICS. 11. SODIUM AND POTASSIUM CHLORIDES AND BROMIDES FROM 0 TO 30°1 BY BENTON B. OWENAND PAULL. KRONICK~ Contribution No. 1614from the Sterling Chemistry Laboratory, Yale University, New Haven, Conn. Received June 83, 1060
The velocity of sound in pure water and in dilute aqueoue solutions of sodium and potmsium chlorides and bromides is reported at 5' intervals from 0 to 30°, and at a frequency of 5 megcy./sec. The isothermal partial molal compressibilities of the salts at infinite dilution, are calculated, and found to increase (become more positive) with increasing temperature.
Introduction The first paper of this series3 contained a description of the movable-reflector acoustic interferometer and the experimental technique by which sound velocities were measured, and the results of these measurements on solutions of sodium and potassium chlorides were used to illustrate the evaluation of R20 for these salts a t 25'. The present paper reports the results of more extensive measurements on solutions of these salts, as well as sodium and potassium bromides, a t 5" intervals from 0 to 30". Experimental In the preparation of the sodium and potassium chlorides, Analyzed C.P. grade salts were used without further purification, but the bromides were recrystallized once from distilled water. The concentration of each solution used in a velocity measurement waa determined by withdrawing a portion from the interferometer and performing a differential potentiometric titration' against a 0.07 N solution of silver nitrate. This silver nitrate solution w m standardized periodically against a thoroughly dried sample of sodium chloride purified by the method of Meites.6 The operation of the interferometer and associated electronic equipment followed closely the procedure previously outlined,a and need not be described again. All velocity measurements were made at 5 megacycles ( f 5 cycles) per second. Temperature wrts controlled to f0.002" during (1) This communication contains material from a thesis presented by Paul L. Kronick to the Graduate School of Yale University in partial fulfillment of the requirement. for the degree of Doctor of Philosophy, June, 1957. (2) The Franklin Institute, Philadelphia 3, Pa. (3) B. B. Owen and H. L. Simona, THIEJOURNAL, 61, 479 (1957). (4) N. F. Hall, M. A. Jenaen and 9. A. Baeckstrom, J . Am. Chem. SOC.,50, 2317 (1928). (5) L. Meites, J . Chsm. Ed., 29, 74 (1952).
the course of the measurements, so that the variation of the velocitx of sound with concentration waa obtained "isothermally. The absolute value of the temperature was, however, not known to much better than 0.01" because a discordance of 0.004" developed between the calibrations of two of our three platinum resistance thermometers while the measurements were in progress. Since our apparatus was designed for precise mertsurement of changes in velocity rather than absolute magnitudes, the instrumental constant (a function of the angles formed by the screw and the guide rods) was evaluated from the known velocity of sound in pure water at 30". For this standard of reference, u~(30'), we used 1509.55 m./sec., the mean of 1509.44 reported by Greenspan and Tschiegp from the National Bureau of Standards, and 1509.66 reported by Wilsoneb from the United States Naval Ordnance Laboratory. The instrumental constant at lower temperatures was calculated from the value a t 30" and the coefficient of linear expansion of stainless steel (10-6 deg.-l).
Results of the Velocity Measurements For each salt a t a given temperature, the velocity of sound was determined in from seven to fourteen solutions whose composition ranged from 0 to 0.07 normal. The results of these measurements could be represented within the limits of their reproducibility ( f0.02 m./sec.) by the equation u = u~
+ A,c + B,c'/r
(1)
The coefficient A , is the quantit which contributes directly to the desired value of or $KO, through the equation
to,
+KO
= lOOOAa
+ 6o+v0 + (2$v0 - Mz/& - 2000
Au/Uo)Pos
(2)
in which &, is the adiabatic compressibility of (6) (a) M. Greenspan a d C. E. Teohiegg, J . Research NaU. b u r . Standards, 59, 249 (1957): (b) W. D. Wilson, J . Acouat. SOC.A m . . 81, 10G7 (1959).
Jan., 1961
85
S T A N D A R D P A R T I A L 3 I O L A L C O M P R E S S I B I L I T I E S BY vLTRASOXICS
pure water, and the quantities As and 6" are correction terms3 which convert to isothermal compressibilities. M z is the molecular weight of the salt, and do is the density of pure water. Under the conditions of our measurements the last term in equation 1 contributes so little to u that the value of 23, cannot be determined precisely. Improvement in the evaluation of B, by using a greater number of solutions and higher concentrations was not attempted because equation 1 is theoretically justified only a t extreme dilution, and a statistically significant increase in the number of measurements per run could only be attained by seriously limiting the temperature range, or the number of salts investigated.
I
'
TABLEI PARAMETERS OF EQUATION (1) t, oc.
uo"
Au b
Au
@
Sodium chloride ( B , = -3.1)
0 5 10 15 20 25 30
1402.99 1426.73 1447.79 1466.40 1482.75 1496.70d 1509.64
80.20 76.09 72.73 70.17 67.67 64.53d 61.47 Potatssium chloride (Bu = -7.2) 1402.98 73.58 1426.70 69.28 1447.81 65.28 1462.40 62.31 1482.73 60.10 1496.76d 57.20d 1509.56 53.79 Sodium bromide ( B , = -3.2) 1402.97 45.88 1426.70 41.69 1447.78 37.83 1466.40 34.41 1482.75 32.40 1497.07 28.54 1509.49 26.18 Potsmiurn bromide (Bu = -5.2) 1402.99 38.37 1426.70 33.55 1447.79 29.74 1466.40 26.09 1482.73 23.53 1497.05 20.80 1509.51 18.06
0
20
10
30
t, "C.
80.1 76.6 73.3 70.2 67.3 64.6 62.1
Fig. 1.-Variation of A , with tem erature. Reading from top to bottom, the salts are: NaCt KC1, NaBr and KBr.
varying less than the difference between values derived from the data on different salt solutions. Unfortunately, A , is sensitive to a change in B,, varying as much as 10% in one extreme case. The 0 73.1 results of this second curve-fitting are collected in 5 69.2 Table I, which also includes smoothed values of 10 65.6 A , read from the plots of A , against temperature 15 62.3 which are illustrated in Fig. 1. The variation in 20 59.3 A, produced by changing B, from the individual 25 56.6 preliminary values to the average values recorded 30 54.2 in Table I is indicated by the lengths of the vertical tails on the data points, except for the results a t 25" for sodium and potassium chlorides. For these 0 45.3 two salts the data a t 25" represent results obtained 5 41.4 at several frequencies,a and the Iengths of the tails 10 37.8 are equal to the greatest variation in A , produced 15 34.5 by changing from the individual values of B,, for 20 31.5 any one of four series of measurements, to the com25 28.8 posite value designated as "com" in Table I of 30 26.4 the previous paper.* The variations in A , may be summarized as 0 38.3 follows: 1 unit, or less, for 50% of the points, 2 5 34.0 units for 25010, and about 3 units for the remaining 10 30.1 25% with an outstanding single variation of 5.4 15 26.6 units for sodium chloride a t 30". The larger 20 variations emphasize the extreme difficulty of de23.5 25 20.8 termining A,, the individual limiting change in 30 18.5 sound velocity with concentration, from the nonThese values differ from those recorded in Table VI of linear equation 1. On the other hand, these exref. 1 by the factor 0.999874,introduced to change the aver- treme variations are much too large to be conage value a t 30' from 1509.74 to 1509.55 m./sec. *From sidered a measure of the uncertainties in the equation 1 and the average values of B, indicated. Smoothed values obtained graphically from the plot illus- smoothed values of A , (Table I) which were deTaken from ref. 3 without change: NaCl rived from a whole family of curves, obtained by trated in Fig. 1. -3.0) and KC1 (Bu = -6.0). (B. combining eight from the previous paper3 with the twenty-eight reported here. A preliminary least-square representation of the At each temperature we have averaged the four data by equation 1 showed that there was no con- values UQ to be found in Table I, and recorded sistent trend in B, with temperature. Accordingly, them asofuo(exp.) in the second column of Table 11. average values of B,, independent of temperature, Values of uo calculated from the empirical equation were calculated for each salt and then used to redetermine uo and A,. The values of uo were uo 1403.00 + 5.02061 - 0.05700t2+ 0.000267W (3) practically unaffected by this second curve-fitting, are recorded in the third column, and represent 0
@
BENTON B. OWENAND PAULL. KROXICK
86
TABLE I1 PROPERTIES OF PUREWATER uo (exp.) UO 106b80S lo6 60 los80 0 1402.98 1403.00 50.811 0.0300 50.841 5 1426.71 1426.71 49.130 .0017 49.132 10 1447.79 1447.77 47.723 .0522 47.775 15 1466.40 1466.39 46.547 .I567 46.704 20 1482.74 1482.75 45.566 .2998 45.866 25 1497.06 1497.07" 44.751 .4726 45.224 30 1509.58 1509.55 44.076 ,6695 44.746 The two values a t 25" marked with d i n Table I were excluded from the average because of a change in the instrumental constant. t , OC.
the experimental values satisfactorily. Because of the temperature smoothing, uo calculated from equation 3 will be used in subsequent calculations. The adiabatic compressibility of pure water (expressed as bars-') was calculated by the equation pos
=
100/u02d0
(4)
and recorded in the fourth column of Table 11. The quantity 6,,,which appears in the fifth column, was calculated from the equation 60 =
60 - pus
=
Tao2/10~p&
tion, are available only at 25", and at the temperature of maximum density, where A s is zero. Since the term lOOOAs contributes only about 7.5% to +KO at 25", we have assumed a convenient linear temperature dependence in order to estimate A6 As = ( t
(7) H. 6. Harned and B. B. Owen, "The Physics1 Chemistry of Electrolytic Solutions," Third Edition, Reinhold Publ. Corp., New York, N. Y., 1958. (8) N. S. Osborne, H. F. Stimson and D . C. Ginnings, J . Research Noli. Bur. Standards, as, 197 (1939). Equation 5 requires that cp be expressed in joules/$. deg. C. (9) Densities in ref. 7 are g . / r n l . Equations 4 and 5 require that do be expressed as g./co. (19) W,Geffokon, 2 , phyeik. Cham., 166& 1 (1931)b
- 3.986)Aa (25")/21.014
(6)
at temperatures other than 25 and 3.986'. Values of lOOOA6 are recorded in Table 111, which completes the tabulation of all of the quantities which TABLE I11 STANDARD PARTIAL MOLALCOMPRESSIBILITIES, azo(= @). AND ASSOCIATED QUANTITIES t , "C.
+vQ
107 ~6
104 FIo
0 5 10 15 20 25 30
Sodium chloride 12.4 -0.73 13.4 .19 14.3 1.11 15.1 2.02 15.8 2.94 16.35 3.86 16.8 4.78
-75.85 -68.12 -61.47 -55.69 -50.65 -46.28 -42.44
0 5 10 15 20 25 30
Potassium chloride 23.0 -0.58 23.9 .I5 24.7 .88 25.4 1.61 26.0 2.33 26.45 3.06 26.8 3.79
-68.04 -60.66 -54.38 -49.00 -44.38 -40.44 -37.06
0 5 10 15 20 25 30
Sodium bromide 19.0 -0.87 20.1 .22 21.1 1.32 22.0 2.41 22.8 3.51 23.45 4.60 24.0 5.70
-66.67 -59.10 -52.58 -46.92 -41.98 -37.70 -33.96
0 5 10 15 20 25 30
Potassium bromide 29.6 -0.72 30.6 .18 31.5 1.09 32.3 1.99 33.0 2.90 33.55 3.81 34.0 4.71
-58.86 -51.64 -45.49 -40.22 -35.70 -31.86 -28.58
(5)
using values for the coefficient of thermal expansion?, specific heat* and densityg of pure water to be found in the literature. The isothermal compressibility, Po, of pure water, calculated from equations 4 and 5, is given in the last column of Table 11. We consider these values somewhat more reliable than those calculated from direct measurements of compressions resulting from large pressure increments.? Calculation of 4 ~ 0(= E20).-The calculation of ~ K O , and hence KZ0, by equation 2 requires knowledge of the two quantities t$v0 and As at all of the temperatures with which we are concerned. At 25" several sources of data7 are available for evaluating +vo for the four salts under study, but in order t o obtain 4v0 a t 5" intervals from 0 to 30" a very uncertain interpolation must be made between the values available a t 0, 25, 35, 45 and 50". Geffcken10 extrapolated the data a t these temperatures in 1931. Although additional data are now available a t 25", and better extrapolations have been performed a t this temperature, it was decided in the interests of smooth and consistent interpolation t o use only Geffcken's reported values of 4 ~ 0 , and to treat his results for the four salts as a family of very similar curves. This led to the smooth values of horecorded in Table 111. The uncertainty in these values is high, and probably exceeds that of the smooth values of A, given in Table I. Fortunately, +KO is very simply corrected by equation 2 for future improvement in the values of +vO at any particular temperature. The data from which to calculate7 A6, the rate of change of 6 with concentration a t infinite dilu-
Vol. 65
appear in equation 2 except the molecular weights, M z , and the density of pure water, do. Our values of +KO calculated by this equation are given in the last column of Table 111. Although the accuracy with which these quantities are presently known might not justify retention of the last two decimal places, we have recorded 4x0 to four figures so that future improvements in any of the critical quantities A,, +v0 and A s may be used very simply t o yield more precise values of +KO. These results show that K,o is negative, and increases rapidly (becomes more positive) with increasing temperature. The rate of increase decreases with rise in temperature, suggesting that Kzo may pass through a maximum above 50". is, of course an additive property of the ions. The high degree of additivity observed in the
Jan., 1961
SEPARATIOK OF HS,HD
BY GAS CHROMATOGRAPHY
AND
87
values recorded in Table I11 should be regarded of Aa make this an additive quantity, and it as a necessary condition, but not as a proof of ac- follows from equation 2 that A , must also be an curacy, for the curves from which 4v0,Aa and A, additive property of the ions. The application of were read had been carefully constructed to ensure this principle was very helpful in limiting the posiadditivity of th'ese quantities, as well as tempera- tions of the curves in Fig. 1, because it had the effect ture smoothing. The definition'l and calculation of increasing the number of data points which had (11) Ref. 7. p. 387. to be considered simult~aneously.
THE SEPARATION OF HYDROGEN, DEUTERIUM AND HYDROGEE DEUTERIDE MIXTURES BY GAS CHROMBTOGRAPHY BY PAULP. HUNTAND HILTOX A. SMITH Department of Chemastry, Universaty o j Tennessee, Knoxcalle, Tennessee Receiued June $0, 1960
The resolution and analysis of t h e components of hydrogen-deuterium mixtures have been accomplished by gas chromatography a t 77°K. Neon was employed as the carrier gas, and the column was chromia deposited on alumina. Orthohydrogen and parahydrogen did not separate on the chromia-alumina column. The separation factor for hydrogen deuteride and deuterium was much greater than that for hydrogen and hydrogen deuteride. The complete separation of deuterium and hydrogen deuteride was also obtained on a silica gel column with hydrogen as the carrier gas, whereas a charcoal column produced very little separation.
Gas chromatography affords a simple method for t'he analysis of t'he hydrogen isotopes. Various degrees of separation have been reported by several investigators. l--B A recent preliminary communications describes the first complete separation of hydrogen, hydrogen deuteride and deuterium by this method. The resolution was accomplished by means of a chromia-alumina column operated at 77'K. with neon as the carrier gas. Details of this separation. as well as experiments with other columns are given in the present contribution. Experimental Apparatus .-The chromia-alumina column consisted of a single piece of copper tubing 12 ft. in length and with an outside diameter of 5/16 in. Grade F-1, 8-14 mesh, activated alumina, obtained from the Aluminum Company of America, was crushed and screened through a series of standard screens. The column packing was prepared from 225 g. of 20-40 mesh alumina to which 6.7y0by weight chromium trioxide was added in 350 ml. of water. The mixture was agitated for three hours and the excess liquid was removed b y filtration. The residue was dried and the chromic acid reduced in a stream of hydrogen at 360". The yellow material turned green upon reduction. Small dust particles were removed by screening following the reduction process. After the column was packed and coiled in a spiral 4 in. in (diameter, water was added to the column in order to obtain partial deactivation. Considerable evolution of heat was noted as the water was added. The column was reactivated when desired by passing a stream 2f nitrogen through the column for three hours a t 140-150 . -4circulatory gas flow system with neon as the carrier gas was employed with the chromia-alumina column. (1) E. Glueckauf and G. P. Kitt, in D. H. Desty, "Vapor Phase Chromatography," Butterworths Scientific Publications, London, 1957, pp. 422-427; E. Glueckauf and G. P. Kitt, in the "Proceedings of the International Symposium on Isotope Separation," Interscience Publishers, Inc., New York, N. Y.,1958, pp. 210-226. (2) C. 0. Thomas and H. A. Smith, J . Phys. Chem., 63, 427 (1959). (3) W. R . Moore and H. R. Ward, J . A m . Chem. Soc., 80, 2909 (1958). (4) W.A. \'an
Hook and P. H. Emmett, J . P h y s . Chem., 64, 673 (1960). (5) 9.Ohkoshi, Y. Fujita and T. Kwan, Bull. Chem. SOC.Japan, 31, 770 (1958); S. Ohkosbi, S. Tenma, Y.Fujita and T. Kwan, ibid., 31, 772 ( 1 9 5 8 ) ; S. Ohkoehi, S. Tenma, Y.Fujita and T. Kwan, ibid., 81, 773 (1958). (6) H. A. Smith and P. P. Hunt, J . P h p . Chem., 64, 383 (1960).
A double-acting, piston-type pump furnished sufficient pressure differential for gas flow. The construction of the gas pump was similar to those previously described.7~8with the following modifications. The piston barrel, a proximately 5 in. long, was constructed from 12-mm. yrex glass tubing. A Teflon-covered magnetic plunger, 1.5 in. in length, was fitted inside the chamber. The outlet and inlet connections t o the piston barrel were made of Pyrex tubing with an outside diameter of 6 mm. Valves were constructed from sections of 9-mm: glass tubing approximately in. in length, fitted over 1/2-in. sections of 6-mm. capillary tubing. The capillary tubing was ground on the end, and a section of a microscope cover glass was seated in the narrow space between the capillary end and the connection between the 6- and 9mm. tubing. Indentations were made at the taper seal between the 9- and 6-mm. tubing just above the cover g!ass to prevent the cover glass from turning edgewise and sticking during the pumping process. The inlet leads from each end of the pump were connected together with glass tubing, as were also the outlet leads. The plunger was moved by two doughnut-shaped Indox magnets obtained from the Indiana Steel Products Company of Valparaiso, Indiana. The magnets were clamped in a brass carrier. The magnet carrier was connected by means of a string across a pulley to a disc attached to a motor to furnish reciprocal movement of the plunger. A slot cut in a disc allowed the stroke length to be properly adjusted. The motor speed was 45 r.p.m. The system was prepared for operation by evacuation and flushing with hydrogen and neon. The entire apparatus was then filled with neon to a pressure slightly greater than that of the atmosphere. When the column was immersed in liquid nitrogen, it was necessary to add more neon to maintain this pressure. The hydrogen and deuterium samples were oxidized in a hot copper tube after the samples had passed through the katharometer. The resulting water was adsorbed in silica gel and charcoal traps. The flow rate was measured bv a soap-film meters placed in the circulatory system. Neon was conserved between a series of runs by absorbing the excess from the column in the charcoal trap immersed in liquid nitrogen. Silica gel columns, 6 and 10 ft. in length, were prepared from 40-60 and 60-80 mesh material obtained from the Davison Chemical Company. The packing was activated at 140-150° before being placed in the column. Hydrogen,
5
(7) J. C. Balabaugh, R. G. Larsen and D. .4. Lyon, Ind. EnQ.Chem.. cis2 (1936). (8) F. D.Rosen, Rev. Sd.Inetr., 84, 1061 (1953). (9) C. 0. Thomas and H. A. Smith, J . Chem. Educ, 86, 527 (1953).
as,
