NOTES
804
SOME THERMODYNAMIC PROPERTIES OF LIQUID CHLOROETHANE BY JAMESW. GILBERTAND ROBERTT. LAQEMANN Contribution Jrom the Department OJ Physics and Astronomy, Vanderbilt University. Nashville, Tennessee Received November 18, 1966
Very little information is available on the thermodynaniic properties of the rather important compound chloroethane (CzH6C1) in the liquid phase. Certain of these, such as the specific heat a t constant volume, are difficult to measure directly, but a determination of the velocity of compressional waves, which is relatively easy to carry out, enables one to calculate various properties if values of the density and specific heat a t constant pressure are known. This has been done using reagent grade chloroethane purified in a 30-plate, low temperature column. Experimental The velocity of sound measurements were made by the interferometer method using equipment very similar to that described by McMillan and Lagemann.' Instead of being made of metal, the reservoir and reflector were fabricated from Fluorothene. The reflector was connected to the micrometer shaft by a ball and socket joint of Fluorothene which permitted easy alignment of the reflector when brought against the bottom of the liquid reservoir. Electrical contact tb the top of the quartz crystal was effected by means of a thin, flexible strip of aluminum foil placed between the quartz crystal and the Fluorothene reservoir. An opening in the foil, smaller in size than the crystal, served to retain a drop of mineral oil which acted as a transducer. Care was taken to maintain constant temperature by placing the interferometer in a thermostated water-bath. I
IL
I
I\
-
-
Vol. 60
Also the frequency of the oscillator (500 kc./sec.) was checked by comparison with station WWV of the National Bureau of Standards. Several runs were made going from a high temperature of 12' to a low temperature of minus 14' (and return), with such good reproducibility that it is believed the samples remained pure while under study. Three different sainples were used. The density of liquid chloroethane had been measured before,2 but because of the variation in the results of the various experimenters and because no values were available below O", new determinations have been made. Because of the high volatility of chloroethane, the picnometers (5 and 3 ml. capacity) used were equipped with capillary side arms. Even so, to avoid introducing significant errors due to evaporation losses, it was found necessary to make distinct mass measurements at each temperature a t which the volume was determined. To prevent unduly large expansion and subsequent loss of liquid, as the picnometer was moved from ambient temperature into the bath, or vice versa, the density measurements were made in a cold room maintained a t about 2'.
Results The results of the density and velocity measurrments are given in Table I. For comparison purposes Fig. l shows the values of density obtained by various workers. It can be seen that the present work is well substantiated. TABLE I MEASUREDVALUES OF THE DENSITY AND ULTRASONIC VELOCITY OF I,IQWIDCHLOROETHANE Temp., OC.
Density, g./cc.
Ultrasonic velooity, ni./sec.
12 11 10 9
0.9063 1043 ,9079" 1045 1050 .9094' .9107 1054 1059" 8 .9123 1068 6 .9150 3 .9193 1082 a Obtained by interpolation.
Temp., OC.
Density, g./cc.
Ultrasonic velocity rn./sec.'
0 3 6 -9 -12 -14
0.9237 .9278 .9321 ,9364 .9407 ,9434
1094 1109 1125 1139 1153 1162
-
-
The specific heat a t constant pressure is knowns over a range of temperatures, so that, combined with the density and velocity of sound measurements, it is possible to calculate certain other thermodynamic properties. The following welliknown relations4 were used for this purpose
y =BL ! = C2 UAYE AND L A B Y
0
PRESENT
Bad
s(
WORK
BUR
OF S T A N D
TIMMERMAN
%
OTHERS
FROM
REFERENCE 2
I
I
I
I
I
I
-15
-10
-5
0
5
10
,9000
TEMPERATURE,
Fig. ].-Density
II 15
* C.
of liquid chloroethane as a function of temperature.
(1) D. R.MoMillan and R. T. Lagemann, J . Acousl. SOC.A m . , 19, 956 (1947).
Cy
(4)
I n the above V is the ultrasonic velocity; d, the density; B e d , the adiabatic compressibility; B i s , the isothermal compressibility; a, the volume coefficient of expansion; J, the mechanical equivalent of heat; y, the ratio of specific heats; cp, the specific heat a t constant pressure; and cv, the specific heat at constant volume; all measured at (2) See the aummrry by M. J. Timmermans and Mme. HennautRoland, J . chim. phys., 34, 693 (1937); C. F. Jenkin and D. N. Shorthose, Ice and Refrigeration, 6 6 , 347 (1924). (3) J. Gordon and W. F. Giauque, J . A m . Chem. Soc.. 7 0 , 1506 (1948). (4) M. W. Zemansky, "Heat and Thermodynamics," 3rd ed., MoGraw-Hill Book Co., New York, N. Y.,1961.
805
NOTES
June, 1956
TABLE I1 SOMETHERMODYNAMIC PROPERTIES OF LIQUIDCHLOROETHANE l’riiip., “C.
Coefficient of expansion
(Qc.)-I x
cp,a
Bad
cal./g.
(om.2 dyne-]) x 10’2
Bie (cm.2 dyne-!)
Ratio of specific
CY.
cal./g.
dog. heats x 10” 1.461 0.2604 148.3 101.5 12 -1.572 0.3805 1.462 ,2599 147.4 100.8 11 1.570 .3800 1.465 .2590 146.1 99.7 10 1.567 ,3796 1.469 ,2581 145.1 98.8 9 I . 565 ,3791 1.472 ,2573 143.8 97.7 8 1.562 .3787 1.478 ,2556 141.6 95.8 6 1.557 ,3778 1.488 ,2531 138.2 .3765 92.9 3 1.550 1.495 .2510 135.3 90.5 0 1.543 .3752 1,507 .2482 87.6 132.0 ,3740 - 3 1.536 1.518 ,2456 84.8 128.7 ,3727 - 6 1 .520 1.528 ,2430 82.3 125.8 .3714 - 9 1.522 1.538 ,2408 80.0 123.0 .3702 -12 1.515 1.543 ,2393 78.6 121.3 .3693 - 14 1,510 a Read from a curve constructed from data given by Joseph Gordon and W. F. Giauque, J . Am. Chem. Soc., 70, 1506 (1948). the same temperature T. Values of the thermo- chromate methods of analysis were used to standardize acid stock solutions of uranium(VI),2 iron(I1) dynamic properties obtained for a range of tem- phosphoric (stored under nitrogen) and iron(III).S peratures by means of the foregoing relations are The extent of uranium( VI) reduction in phosphoric acid tabulated in Table 11. solutions containing iron( 11) and iron( 111)was determined As might be expected, values of each of the prop- by measuring the optical density a t 630 and 670 mp, using a Beckman model D.U. spectrophotometer. The molar exerties appear to be linear functions of the tem- tinction coefficients for uranium(1V) at these wave lengths perature over the range of temperatures studied. were found to be 31.6 and 38.2, respectively, and were esIn the case of the ultrasonic velocity a negative sentially constant over the phosphoric acid concentration slope (or temperature coefficient) of 4.64 m./sec. range used (1.8-4.8 M). A small correction for the absorption of iron( 111) was necessary, the molar extinction deg. is obtained, in good agreement with a predic- coefficient being 0 16 and 0.20 a t 630 and 670 mp, respection made on the basis of an empirical formula dis- tively. cussed earlier.6 The slope of the density-temDue to the slowness of the reduction a t room temperature, several days were required to reach equilibrium in some perature curve is -1.425 X g . / ~ mdeg. .~ cases. The total reducing power of typical solutions was determined by dichromate titration, the results indicating ( 5 ) R . T. Lagemann, D. R. MoMillan, Jr., and W. E. Woolf, that air oxidation of these solutions (stored in 100-ml. voluJ . Chem. Phvs., 17, 3G9 (1949). metric flasks) was negligible. Since the solutions were stored a t room temperature, the results correspond only approxiTHE REDUCTION OF URANIUM(V1) BY mately to 25’. The e.m.f. of the cell IRON(I1) I N PHOSPHORIC -4CID SOLUTION Pt lFeS04 (0.05 M),Fe2(S04)s(0.025 M),HzSO4 (0.36 M ) , &PO4 (C)l S.C.E. BY C. F. BAES,JR. under argon was measured with an L. & N. type K-2 pate!tiometer and a reflecting galvanometer at 24.7 f 0.1 . Oak Ridge National Laboratory, Oak Ridge, Tennessee In all cases constant readings were reached within 12 minReceived November 14, 1966 utes. The precision of successive measurements on the Uranium(1V) in acidic sulfate solutions is rapidly same solution was usually 0.1 mv. 10,
de&
oxidized to the hexavalent state by iron(III).’ I n the presence of 1-2 M added.phosphoric acid, the oxidation, while slower, still proceeds to completion.2 Some results of Quinn and Watts3 a t the Armour Fertilizer Works revealed, however, that uranium(V1) is slowly reduced by iron(I1) in 6 M phosphoric acid at room temperature. More recently Canning and Dixon4 have reported the quantitative reduction of uranium(V1) by iron(I1) in hot 6 M phosphoric acid. The following brief investigation of this oxidation-reduction system confirms the high dependence of the oxidation-reduction equilibrium on phosphoric acid concentration. Experimental Uranium(V1) sulfate and reagent grades of iron(I1) SUIfate, iron(II1) sulfate, sulfuric acid and phosphoric acid were used to prepare the solutions used. Volumetric di(1) I. M. Kolthoff and J. J. Lingane, J . Am. Chem. Soc., 66, 1871 (1933). (2) J. M.Schreyer and C. F. Baes, Jr., Anal. Chem.,96, 644 (1953). (3) Private communication from P. J. Quinn, 1952. (4) R. G. Canning and P. D t o n , Anal. Chem., 27,877 (1955).
Results Oxidation-Reduction Measurements.-The extent of uranium(V1) reduction by iron(I1) was determined in two series of solutions, all of which were 0.36 M in sulfuric acid and initially ca. 0.01 M in uranium(V1). In the first series the phosphoric acid concentration was held constant a t 3.G8 M and the [Fe(II)]/[Fe(III)] ratio was varied at 0.05 M total iron. The results were consistent with the reaction 2Fe(II) . .
+ U(V1) = 2Fe(III) + U(IV)
[Fe(III)l2 [U(TV)] [Fe(II)IZ [ V ( V n (’) being 13 2 a t ca. 25’,
K =
*
the equilibrium quotient K for equilibrium [Fe(II)]/ [Fe(III)] ratios in the range 0*14-1.7* I n the second series of solutions the initial iron(11) and iron(II1) concentrations were each 0.05 M (5) 1. M. Kolthoff and E. B. Sandell, “Textbook of Quantitative Inorganic Analysis,” Rev. Ed., The Macmillan Co.. New York, N. Y., 1948, p. 609.
