NOTES
2060 Negative Viscosity B Coefficients in Nonaqueous Soivents
by Kent Crickard’ and James 3’.Skinner2 Chemistry Department, Williams College, Williamstown, Massachusetts 01867 (Received September $7, 2968)
The concentration dependence of the viscosity of a q u e o u ~ ~and - ~ nonaqueousaJ electrolytic solutions has been interpreted in terms of the semiempirical JonesDole equations 7/70 =
1
+ AC’” + BC
(1) where 7 and 70 are the solution and solvent viscosities, C is the molarity, and A and B are adjustable parameters. Equation 1 has been found valid to approximatelyS 0.1 M , and above that concentration, a term quadratic in concentration may be addeda8 The square root term represents the contribution to the viscosity from the ion-ion coulombic interactions. Falkenhagenlo derived an expression for the A coefficient in terms of limiting equivalent conductances and solvent properties. The linear term in eq 1 is believed to have its origin in two effects. The first is the disruption of the hydrodynamic streamlines due to the effective size of the ions in solution. The ions themselves may be inherently large relative to the solvent molecules; e.g., tetraalkylammonium ions or the solvated ionic volume or cosphere” may be large. Second, the B coefficient represents any specific electrostatic effect the ions may have on the viscosity of the solvent. This latter phenomenon, with which this investigation is concerned, has been discussed in detail by Frank and coworker^'^,^^ and K a m i n ~ k y . ’ ~In reviewing the viscosity of dilute aqueous electrolyte solutions, these authors proposed that certain ions, e.g., Li+, Na+, and Ag+, could be described as “structure makers,” where they exhibited positive, single-ion B coefficients, indicating enhancement of the hydrogen-bonded, quasicrystalline structure of water. Other ions, e.g., Cs+, I-, and NHkf, which exhibited negative B coefficients, could be described as “structure breakers.” These ions were thought to weaken the hydrogen bonding between solvent molecules in their immediate vicinity and hence to increase the fluidity of the solvent. We believe that, with one e~ception,’~ there has been no report of negative B coefficients in any solvent other than water, and, indeed, a number of texts on the properties of electrolytic solutions suggest that this phenomenon is peculiar to water. Investigations in which solution viscosities were found to be less than the solvent viscosity are discussed below, but these data were not analyzed in terms of the Jones-Dole equation. If the negative B coefficients are in fact related to the highly The Journal of Phgsical Chemistry
associated nature of the water, a logical confirmation might come in work in nonaqueous solvents where hydrogen bonding is known to be pronounced. In the present study the viscosities of ethylene glycol and glycerol solutions of potassium iodide and cesium iodide have been measured at 25”.
Experimental Section Potassium iodide (J. T. Baker Analyzed reagent, 100.0%) was used as received, after drying at 110”. Cesium iodide (A. D. MacKay, Inc., 99.9%) was recrystallized once from methanol (0.03 g/ml of solvent) and dried at 110’. Ethylene glycol and glycerol (Fisher Certified reagents) were dried over anhydrous sodium sulfate for several weeks. Both solvents were distilled under reduced pressure under an atmosphere of dry nitrogen, the middle fraction being collected. All solutions were prepared by weight in flasks previously flushed with dry nitrogen and were shaken overnight in the dark prior to use. Densities were measured in a Sprengel-type pycnometer (22 ml) calibrated with distilled water. Viscosities were measured (25.00 f 0.01’) in Cannon-Fenske Routine viscometers, modified for use in a dry, closed atmosphere. Flow times (400-600 sec) were reproducible to +0.1 sec. The Poiseuille equation relating liquid viscosity to the flow time and dimensions of the viscometer includes a kinetic energy correction.16 Calculations for the viscometers used in the present study showed that for ethylene glycol, the kinetic energy correction amounted to about 0.03% of the viscosity, whereas for glycerol, the correction amounted to about 0.0005%. The term was neglected and the viscosity was calculated from 7 r = 7/70 = Pt/POtO
where
p, po, t,
(2)
and to are the densities and flow times for
(1) This work is based in part on the honors thesis of K. C., 1968. (2) To whom correspondence should be directed. (3) M. Kaminsky, 2. Physik. Chem. (Frankfurt), 5 , 154 (1955). (4) R. L. Kay, T. Vituccio, C. Zawoyski, and D. F. Evans, J . Phys. Chem., 70, 2336 (1966).
(5) M. Yasuda, Bull. Chem. SOC.Japan, 41, 139 (1968). (6) D. Feakins and K. G. Lawrence, J. Chem. Soc., A , 212 (1966). (7) M. D. Archer and R. P. H. Gasser, Trans. Faraday SOC.,62,3451 (1966). (8) G. Jones and M. Dole, J . A m . Chem. SOC.,51, 2950 (1929). (9) M. Kaminsky, 2. Physik. Chem. (Frankfurt), 8 , 173 (1956). (10) H. Falkenhagen and M.Dole, Physik. Z.,30, 611 (1929). (11) R. W. Gurney, “Ionic Processes in Solution,” McGraw-Hill Book Co., h e . , New York, N. Y., 1953, Chapter 9. (12) H. 8. Frank and M. W. Evans, J. Chem. Phys., 13, 507 (1945). (13) H. S. Frank and W.-Y. Wen, Discussions Faraday Soc., 24, 133 (1957). (14) M. Kaminsky, i b i d . , 24, 171 (1957). (15) R. J. Gillespie, Rea. Roy. Austral. Chem. Inst., 9, 1 (1959). A value of -0.1 is given for NHdHS04 in Has04 at 25’. (16) R. H. Stokes and R. Mills, “Viscosity of Electrolytes and Related Properties,” Pergamon Press Inc., New York, N. Y., 1965, Chapter 2.
NOTES Table I : Viscositya of Potassium Iodide in Ethylene Glycol and Glycerol a t 25' --Ethylene
I P
a
10118,
0.0714 0.1361 0.2006 0.2223 0.2526 0.2883 0.4415 0.4804 0.5912 0.8267 0.9156
0.86 1.45 1.84 2.02 2.14 2.35 3.19 3.40 3.89 5.13 5.53
a llsp
glycerol----C, M lO%p
glycol-
C, M
= 9r
-
0.0653 0.1695 0.2326 0.3455 0.4747 0.6150 0.7771
-0.06 -1.38 -2.14 -3.85 -5.45 -7.12 -9.20
1.
Table I1 : Viscosity of Cesium Iodide in Ethylene Glycol and Glycerol at 25' ---Ethylene C, M
-041
I
e'
1 0.5
1 1.0
c+ Figure 1. Viscosity of potassium iodide in various solvents a t 25': O,methanol, ref 17; 0 , ethylene glycol, this work; 0 , ethylene glycol, ref 21; V, water, ref 3; 0 , glycerol, this work; Orglycerol, ref 22.
__-_
glycol--
0.0931 0.1468 0.2169 0.3691 0.4780 0.5766
Glycerol----
102vsp
C, M
lO%p
0.12 -0.31 -0.51 -1.85 -2.23 -2.85
0.0831 0.1586 0 2402 0.3464 0.4656 0.5885
-2.48 -4.64 -7.02 -10.40 -13.99 -17.58
I
Table 111: B Coefficients for Potassium Iodide and Cesium Iodide a t 25' Solvent
1
B
Ref
KI Methanol Ethylene glycol Water Glycerol Glycerol
0.6747 0.0327 -0.0755 -0.185 -0.176
a b
0.68 -0.080 -0.118 -0.408
e b
C
b d
CSI 8
Dimethyl sulfoxide Ethylene glycol Water Glycerol
f b
a G. Jones and H. J. Fornwalt, J . Am. Chem. Soc., 57, 2041 (1935). This work. E See ref 3. Calculated from the data of H. T. Briscoe and W. T. Rinehart, J . Phys. Chem., 46, 387 G. Jones and H. J. Fornwalt, J . Am. (1942). e See ref 7. Chem. Soc., 58, 619 (1936).
'
-0.2t-
- 0.3 I
I
I
085
1.0
I
C" Figure 2. Viscosity of cesium iodide in ethylene glycol ( 0), glycerol ( o ) ,and water ( 0 ) a t 25'.
the solution and solvent, respectively. The B coefficients, determined from the slopes in Figures 1 and 2 , are given in Table 111.
Discussion Kaminsky's3 results indicate that potassium iodide in water at 25' exhibits a slightly negative B coefficient (-0.073) and is therefore a weak "structure breaker," Volume 73, Number 5 June 1959
NOTES
2062 whereas in methanol” this electrolyte gives a large, positive B (0.67). Although there is evidence for hydrogen-bonded association of alcohols from a number of experimental approaches,1s-20from the point of view of viscosity, methanol appears to be similar to the unstructured solvents, dimethylformamide and dimethyl sulfoxide, in which the alkali halide B coefficients are 0.6-0.7. There have been several investigations of the viscosity of ethylene glycol and glycerol solutions of potassium iodide. Getman’s data21are shown in Figure 1 but extrapolation leads to a negative value of A , in disagreement with Falkenhagen’s expression.’o Briscoe22 measured the viscosity of glycerol solutions of potassium iodide at a number of temperatures but did not calculate B coefficients. GolikZ3reported that potassium iodide showed “negative viscosities” in ethylene glycol and glycerol, but the data at low concentration were too sparse and too scattered to permit calculation of B. B coefficients of 0.0327 and -0.185 were obtained for potassium iodide in ethylene glycol and glycerol in the present study. In comparison to the methanol value ( B = 0.6747), these results suggest considerable weakening of the hydrogen bonding in both solvents; in glycerol the effect is sufficiently pronounced to give a negative B. I t is interesting to note that the data in ethylene glycol are linear to about 0.9 -44, far in excess of the limit of validity generally assumed for eq 1. The data in glycerol show two linear regions, one to about 0.3 M ( B = -0.185) and then a second region beyond this concentration. Although more data are needed before an explanation of this phenomenon could be attempted, Fornwalt’s data” for this salt in methanol exhibited the same behavior. Davis and RlalpassZ4have suggested that ion pairing might explain the appearance of two linear regions. Cesium iodide (Figure 2) would be described as a “structure breaker’’ in both ethylene glycol ( B = -0.080) and glycerol ( B = -0.408). The latter value is more negative than any reported in water at any temperature. Although the data in ethylene glycol show some scatter, the data in the other solvent exhibit linearity to about 0.5 M , again in excess of the limit generally assumed for the Jones-Dole equation. I n water, the B coefficient of cesium iodide is more negative than that of potassium iodide. The same relationship holds for these two nonaqueous solvents. For both salts, the B coefficients become increasingly negative in going from ethylene glycol to water to glycerol. It is difficult to rationalize this trend in terms of one solvent parameter, i.e., viscosity, dipole moment, or compressibility, If the negative B coefficients are indicative of a weakening of the hydrogen bonding, the present data suggest that the extent of association should be least in ethylene glycol and most pronounced in glycerol. The Journal of Physical Chemistry
The conductance data of Accascina and Petrucci25 for potassium chloride in ethylene glycol and glycerol have been used to approximate the A coefficients for the systems studied, assuming that the limiting equivalent conductances of cation and anion were equal and independent of the alkali metal or halide. This gave calculated values of A of 0.0058 for ethylene glycol and 0.0034 for glycerol. The experimentally determined value for cesium iodide in the latter solvent was 0.0032, the agreement being somewhat fortuitous, as the values for the other systems were larger than the calculated values. Further work is in progress to include other hydrogen-bonded solvents as well as an investigation of the temperature dependence of B in these solvents. Acknowledgment. The authors gratefully acknowledge funds made available as part of a grant to Williams College by the Alfred P. Sloan Foundation. (17) G. Jones and H. J. Fornwalt, J . Am. Chem. SOC., 57, 2041 (1935). (18) H. Eyring, M. S. Jhon, J. Grosh, and E. R. Van Artsdalen, J. Chem. Phys., 47, 2231 (1967). (19) M. Saunders and J. B. Hyne, ibid., 29, 1319 (1958). (20) G. E.McDuffie, Jr., and T. A. Litovitz, ibid., 37, 1699 (1962). (21) F. H. Getman, J . Am. Chem. SOC.,30, 1077 (1908). (22) H. T. Briscoe and W. T. Rinehart, J . Phys. Chem., 46, 387 (1942). (23) A. Z, Qolik, A. B. Oritshchenko, and A. I. Artemchenko, Dopovidi Akad. Nauk Ukr. R S R , No.6,457 (1954). (24) C. W.Davis and V. E. Malpass, Trans. Faraday SOC.,60, 2075 (1964). (25) F. Accascina and S. Petrucci, Ric. Sci., 29, 1640 (1959); 30, 808 (1960).
The Reaction of Active Nitrogen with Phosphorus Vapor
by S. Khanna, Sharon Furnival, and C. A. Winkler Department of Chemistry, McGill University, Montreal, Canada (Received September 27, 2968)
I n the only study reported of the reaction of active nitrogen with phosphorus vapor, Strutt observed a “hang-fire” effect; i.e., the afterglow was extinguished part of the way down the reaction tube, after which there appeared a flame with a continuous spectrum.’ When the vapor was introduced into the region of the flame, or further downstream, the dark zone disappeared, and the vapor burned at the jet. Red phosphorus was reported to be a product of the reaction (but this might have been mistaken for the nitride). No explanation was offered for the observed behavior. For the present study, relatively simple modifica(1) R. J. Strutt, Proc. Roy. SOC.(London), 86, 56 (1912).
