330
THOMAS A. GOVERA N D PAULG. SEARS
Vol. 60
the hydrogen ion in SiOH groups can be replaced by face areas and water contents. Two pieces of evicalcium ions in solutions of p H greater than five and dence refute this mechanism. First, the similarity less than thirteen (Fig. 7). of (x/rn),,, values at 30 and 82" is inconsistent with 4. The similarity between the surface areas de- the difference in the solubility of silica at the two termined by nitrogen adsorption and those found temperatures. Second, it frequently has been reby sorption measurements assuming a P-cristobal- ported that silicic acid goes into solution slowly.10J2 ite structure indicates that the local order of amor- Alexander, et a1.,'0 found that it was necessary to phous silicas is that of P-cristobalite. The lack of wait 20 days to reach the equilibrium concentration correlation between the surface areas of dried Ludox at room temperature. (measured by nitrogen adsorption) and the sol (deAcknowledgments.-The author wishes to actermined by the sorption method) may be due to knowledge the assistance of Mr. J. Pellicane of the change in orientation of the silica structure on this Laboratory in making the measurements redehydration. Additional study is necessary to establish the ported in this study. Thanks are due to Dr. F. cause of the difference between the "bound" water Pundsack for the well-characterized opaline silica content of opaline silica found in the sorption experi- .and the stimulating discussions on the nature of the ment and the content measured by the ignition surface of silica. The nitrogen adsorption measurements were made by Mr. G. Reimschussel and Miss methods (Table 11). It might be suggested as an alternate mechanism M. Cronin of this Laboratory. The author also that the calcium hydroxide in solution reacts with wishes to thank Dr. Stephen Brunauer (Portland soluble monomeric Si(0H)r (silicic acid), which Cement Association, Skokie, Ill.) for his helpful goes into solution at a rate proportional to the sur- comments on the manuscript.
CONDUCTANCES OF SOME ELECTROLYTES I N I-PROPANOL AT 25" BY T H O M 4 S A. GOVERAND
PAUL
G.
SEARS
Contribution f r o mthe Department of Chemistry, University of Kentucky, Lm*n@on,Kentwky Received Auguat f6,1966
Conductances of sodium and potassium iodides and thiocyanates and of tetraethylammonium and tetra-n-propylammonium bromides and iodides in 1-pro anol have been determined a t 25" for concentrations in the range 8-300 X lo-( N. Limiting equivalent conductances and fisociation constants have been determined by the Shedlovskyextrapolation method. The results indicate that limivng ionic conductances are additive in I-propanol.
Introduction Although many studies2 have been made concerning the properties of solutions of electrolytes in methanol and in ethanol, very few data have been reported regarding the behavior of electrolytes in 1-propanol. Hovorka and Simmsa have reported the most systematic previous study regarding 1propanol solutions; however, their results indicate that the Kohlrausch law of independent ion migration does not apply to electrolytic solutions in this solvent. Inasmuch as this law has been found to be applicable to solutions of electrolytes in methanol, ethanol and most other solvents, their results appear questionable. The purpose of this study, therefore, has been to re-examine the additivity of ionic mobilities in 1-propanol. Experimental 1. Purification of Solvent.-1-Propanol
(Eastman Kodak Co. White Label) was fractionated a t atmospheric pressure through a 120-cm. vacuum-jacketed column acked e t h glass helices. Traces of water were removerfas a minimum-boiling ternary azeotrope using benzene as the third component. The retained nuddle fractions had conductivities of 2 X 10" ohm-' cm.+ or less. (I) Based in part upon a report submitted by Thomas A. Gover in an undergraduate independent work courae in chemistry. (2) D. A. MacInnes, "The Principles of Electrochemistry," Reinhold Publ. Corp., New York, N. Y., p. 356. (3) F. Hovorks and J. C. Simma, J . Am. Chem. SOC.,60, 92 (1937).
2. Salts.-The salts were purified as described prev i o ~ s l y and ~ * ~were dried to constant weight in a vacuum oven a t 70" prior to using. 3. Apparatus and Procedure.-Resistances of the sohtions were measured a t 500, 1000 and 2000 cycles with an assembly consisting of the followin parts having the designated numbers according to the keeds and Northrup Catalog EN-95: Jones conductivity bFidge (4666), tuned audio frequency amphfier (9847), audio frequency oscllator (9842) and telephone receiver (9874). The conductance cells, the constant temperature bath and the experimental procedure have been described adequately in previous paper^.^^^ In converting concentrations from a weight to a volume basis, it was assumed that the densities of the solutions were equal t o that of the solvent. AU weights were corrected to vacuum. The conductivity of a salt was obtained by subtracting the conductivity of the solvent from that of the solution. The following data for 1-propanol at 25' were determined by using several samples of the solvent: density, 0.8008 /ml.; viscosity, 0.0193 poise; dielectric constant, 20.4. &he values for the density compare favorably with those which have been resorted by Dunstan and Tholef The value for the dielectric constant agrees m t h the data reported by Maryott and Smith.' The values of the fundamental constants which were used in the calculation of the Onsager constants were taken from the latest report of the Subcommittee on Fundamental Constants.' (4) D. P. Amea and P. G. Sears, TRIBJOURNAL, 59, 18 (1955). ( 5 ) p. a. Sears, E. D. Wilhoit and L. R. Dawson. ibid., 59,373 (1955). (6) A. E. Dustan and F. B. Thole, J . Chem. Soc., 96, 1556 (1909). (7) A. A. Maryott and E. R. Smith. NBS Ciroular 514, August 10,
1951. ( 8 ) F. D. Rossini, F. T. Ducker. Jr.. H. L. Johnston, L. Pauling and ( I . Vinal,,J. Am. Chem. Sac.. 74, 2699 (1962).
w.
CONDUCTANCES OF ELECTROLYTES I N 1-PROPANOL
Mar., 1956
Results Corresponding values of the equivalent conductance, A, and of the molar concentration, C, are given in Table I. Confirmatory data for another series of solutions for each salt have been omitted for conciseness. However, the data for the two series of solutions in each case agreed within the estimated error of 0.2%.
-
IODIDES THIOCYANATES
25
23
h
TABLE I EQUIVALENT CONDUCTANCES OF SOMESALTSIN PROPANOL AT 25’ c x 104 A c x 10’ A (e) Tetraethylammonium (a) Sodium thiocyanate bromide 0.6134 25.69 1.333 22.83 3.200 21.81 1.243 24.88 2.482 23.69 6.254 20.68 11.04 19.37 4.036 22.59 6.313 21.33 18.13 18.12 26.48 17.01 8.907 20.22 13.86 18.70 (b) Potassium thiocyanate 1.109 24.47 2.534 23.34 5.726 21.68 8.524 20.64 11.64 19.75 15.95 18.74
( f ) Tetraethylammonium iodide 0.7544 26.71 1.405 25.82 2 522 24.61 3.923 23.44 6.789 21.70 10.91 19.99
(c) Sodium iodide 0.8605 22.78 1.666 22.20 3.716 21.28 7.550 20.01 12.55 18.96 19.33 17.84
( g ) Tetra-n-propylammonium bromide 0.6610 23.23 1.509 22.27 3.189 21.14 5.737 19.86 9.763 18.41 14.95 17.11
(d) Potassium iodide 0.5946 24.60 1.334 23.82 2.403 23.04 4.199 21.97 7.292 20.61 11.60 19.31
I I1
33 1
(h) Tetra-n-propylammonium iodide 0.6031 1.513 3.216 5.653 9.541 15.13
24.45 23.36 21.86 20.44 18.79 17.19
Discussion Figure 1 shows Kohlrausch plots for the potassium and sodium thiocyanates and iodides in l-propanol. The plots for the potassium salts are approximately parallel and have limiting slopes which are slightly more than 100% greater than the calculated Onsager slopes. In like manner, the plots for the sodium salt exhibit parallelism and have slopes which are about 60y0 numerically greater than the corresponding Onsager slopes. Owing to their nature, one would expect the plots for the potassium and sodium salts with a common anion to intersect at about 0.0025 N . Since the slopes of the Kohlrausch plots for the quaternary ammonium bromides and iodides were found also to be considerably greater than those calculated by the Onsager equation, values of the limiting equivalent conductance, &, and the dissociation constant, K , for
21 NASCN
\
19
KI NAI
t I7b
I
3
2
4
5
JT
100 Fig. 1.-Kohlrausch plots for potassium and sodium iodides and thiocyanates in 1-propanol at 25’.
each salt were calculated by the Fuoss-Shedlovsky method.9 Figure 2 shows linear plots of SA versus cf2S2A2for the quaternary ammonium salts in 1propanol. Plots for the potassium sodium salts are very similar. Table I1 contains the values of A0 and K which were obtained for each salt by this method. The results indicate that dissociation occurs to a greater extent for sodium than for corresponding potassium salts and for bromides than for corresponding iodides. This may be explained on the basis that the greater charge densities of the sodium and the bromide ions probably enhance solvation effects. If the sodium and the bromide ions are more solvated than the potassium and the iodide ions, respectively, in 1-propanol, the Bjerrum “a” parameter (or distance of closest approach) should be greater for the salts containing the sodium and the bromide ions. Inasmuch as the energy required for dissociation vanes inversely with the ‘(a” parameter, the salts characterized by the larger ‘(a” values should be more dissociated. Supporting experimental verification of this appears in the data showing that the tetra-n-propylammonium salts are more dissociated than the corresponding tetraethylammonium salts. TABLE I1 LIMITINGEQUIVALENT CONDUCTANCES AND DISSOCIATION CONSTANTS FOR SOMESALTSIN I-PROPANOL AT 25’ Salt
bo
KI NaI KSCN NaSCN
25.75 23.92 26.12 24.40
K X
103
3.0 5.3 3.1 4.1
Salt
Ao
EtdNI EtaNBr Pr4N PrlNBr
28.55 27.10 25.88 24.50
K X 10a 1.7 2.0 2.0 2.6
The difference between the conductances of corresponding potassium and sodium salts was found to be 1.83 f 0.10 and 1.72 f 0.10 ohm-l cm.2 equiv.-‘, respectively, for the iodides and the thiocyanates. The difference between the conductances of corresponding iodides and bromides was found to be 1.45 f 0.11 and 1.38 f 0.lOohm-1 cm.2 equiv.-l, respectively, for the tetraethylammonium and tetra-n-propylammonium salts. The (9) R.M.FuossandT.Shedlovaky,J. A m . Chem.Soa.,Tl, 1496(1@49),
332
D. N. CLEWAND R. E. ROBERTSON
Vol. 60
in Table 11. The difference between the limiting equivalent conductances of corresponding potassium and sodium salts which can be determined 28 from their data is 1.30 and 5.36 ohm-' equiv.-', respectively, for the iodides and bromides. Their data also indicate that the difference between the limiting equivalent conductances of the corresponding iodides and bromides is 2.23 and 5.63 ohm-' cm.2 equiv.-', respectively, for the potassium and the sodium salts. Their findings and those presented in this paper obviously differ appreciably. Owing to the very limited solubilities of the alkali metal bromides in 1-propanol, an exNI tremely difficult problem exists in obtaining accurate conductance data for a concentration range sufPR,NBR 20/ ficiently broad to permit a good extrapolation to the 1% 6 IO I5 2 b 25 30 i5 the limiting equivalent conductance value. The Aov0 product varies from 0.46 to 0.55 ohm-' C f2S2A' cm.2 equiv.-l poise for the salts in 1-propanol and Fig. 2.-Shedlovsky plots for some quaternary ammonium is of smaller magnitude than that which is found for salts in 1-propanol at 25". most other non-aqueous systems. For the potasuncertainties designated for the differences are sium and sodium salts it is interesting to note that based upon the estimation that the combined ex- the hoqoproduct has approximate relative values of perimental and extrapolation errors do not exceed 1.00, 0.89 and 0.80 for methanol, ethanol and 10.2%. The above corresponding differences show propanol, respectively. For this homologous series good agreement within the limits of the estimated it appears that the product for many salts decreases error aiid provide convincing evidence that the as the size of the molecules and the molecular weight Kohlrausch law of independent ion migration ap- of the solvent increases. A similar effect has been observed for a homologous series of monomethyl plies t o solutions of salts in 1-propanol. For a comparison with previous studies, Hovorka acid amides.I* Acknowledgment.-The authors of this paper and Simms4have reported values of 25.42 and 24.12 ohm-' cm.* equiv. - I for limiting equivalent con- wish to express their appreciation to the Kentucky ductarices of potassium and sodium iodides respec- Research Foundation and to the Signal Corps for tively in 1-propanol at 25". These values are 1.2% the use of several items of equipment in the perless for potassium iodide and 0.8% greater for so- formance of this research. dium iodide than the corresponding values listed (10) R. H. Graves, Dissertation, University of Kentucky, 1953.
3 0 /'\
-
'
THE SPECTROPHOTOMETRIC DETERMINATION OF THE SOLUBILITY OF CUMENE IN WATER BY A KINETIC METHOD BY D. N. GLEW'*AND R. E. ROBERTSON Division of Pure Chemistry, National Research Coum'l,1b OuCrrw, Canudu Received August 16. 1066
A continuous circulation cell is described for the spectrophotometric determination of reactions in solution at constant temperature. The saturation solubility of cumene in water between 25 and 80" and the reaction velocity constants for the transfer of cumene t o and from the aqueous hase have been determined by a kinetic method. The solubility and thermodynamic functions of aqueous cumene are &cussed in terms of a model, generally applicable to all non-ionized aqueous solutions.
Introduction A continuous circulation cell is described for the sDectroDhotometric studv of reactions in solution. The sohbility of cumen;! in water between 25 and 80" has been determined by a direct method which eliminates the inconvenience of extraction2and dilutio1i3 techniques. Theory for the kinetic approach to equilibrium is given and a method is developed for the determination of equilibrium constants from ( 1 ) (a) National Research Council of Canada Postdoctorate Fellow, 1952-1954. (b) N.R.C. Contribution No. 3857. ( 2 ) L. J. Andrews and R. M. Keefer, J . Am. Chem. Soc.. 71. 5034 (1950). (3) R . L. Bolion and W. P.Claussen, ibid.. 73, 1571 (1951).
kinetic measurements. Thermodynamic functions for the equilibria have been calculated and are disLiquid
sntunted aqueous solution
vapor
cussed in terms of a model applicable to all nonionized aqueous solutions. Apparatus.-A general description of the apparatus used in the determination has been given elywhere.' The cumene was floated on the surface of the main body of the water and the aqueous solution was pumped steadily by a small induction motoe in a closed circuit through the quartz adsorption cell where its optical density was measured and on return swept over the hydrocarbon-water interface. (4) D. N. Glew and R. E. Rohertaon. J . Sei. Insfr.. in press. (5) D. Micliell. J . Applied Chcm.. 1, Suyplciucnt No. 1. $8 (1951).
