July, 195G
CONDUCTANCES OF AQUEOUS SODIUM AND POTASSIUM CHLORIDE
surface. The bulk concentration required to form hemi-micelles adjacent to the surface is roughly proportional to the bulk critical micelle concentration for the different aminium acetates. Aminium ions containing eight or less carbon atoms act as surface-inactive counter ions, similar t o ammonium and sodium ions. I n the presence of a large amount of sodium ions, hemi-micelles do not form until the bulk concentration of aminium ions is considerably greater than the concentration required to form them in conductivity water. This is the reverse of the effect of a high concentration of sodium chloride on the bulk critical micelle concentration, in which case the bulk critical micelle concentration is lowered and not raised. At the quartz surface, competition between aminium and sodium ions keeps aminium ions out of the double layer until
985
the bulk concentration of aminium ions approaches that of the sodium ions. Solution pH plays an important role in the formation of hemi-micelles because hydrogen and hydroxyl ions are potential-determining ions for quartz. An increase in pH aids hemi-micelle formation because i t increases the adsorption of counter ions. Acknowledgments.-The author wishes to acknowledge the thought-provoking discussions he had with Professor A. M. Gaudin (M.I.T.), Professor J. Th. G. Overbeek (University of Utrecht, Netherlands), Professor P. L. de Bruyn (M.I.T.), and Mr. F. F. Aplan (M.I.T.) on this subject. The author is indebted to Dr. H. J. Hanvood (Armour and Company, Chicago) for the samples of aminium acetates. The work was sponsored by the United States Atomic Energy Commission.
CONDUCTANCES OF CONCENTRATED AQUEOUS SODIUM Ah'D POTASSIUM CHLORIDE SOLUTIONS AT 85' BY J. F. CHAMBERS,' JEAN M. STOKES~ AND R. H. STOKES~ Chemistry Department, University of Western Australia, Nedlands, Australia Received Februaru IS,1866
Precise conductance measurements are reported for aqueous potassium and sodium chloride solutions in the region from 0.1 N to saturation at 25", and values a t round concentrations are tabulated.
Introduction Since the development of the interionic attraction theory of electrolyte solutions, a tremendous amount of careful work has been devoted to the conductance of dilute solutions, especially in the region below 0.1 mole l.-I, but more concentrated solutions have been relatively neglected. Thus the literature contains no data of modern accuracy for even such common salts as potassium chloride and sodium chloride at 25" above about 0.2 mole l.-I, with the exception of J o n e P absolute determination of the specific conductance of one-demal potassium chloride. Since recent theoretical dev e l o p m e n t ~ ~offer - ~ promise of supplying an adequate theory for concentrated solutions, we are studying the conductances of some simple salts over a wide range of concentration and temperature, the first results being now reported. Experimental Sodium chloride was of analytical reagent quality, dried for 24 hours a t 400'. Part of the material was further purified by precipitation with hydrogen chloride gas; the product however gave results indistinguishable from those for the original material. Potassium chloride was analytical reagent material purified by recrystallization from conductance water and similarly dried; fusion was also tried (1) Electrolytic Zinc Company Research Fellow, 1955. (2) Chemistry Department, University of New England, Armidale, N.S. W., Australia. (3) G . Jones and B. C. Bradshaw, J . A n . Chem. SOC.,116, 1780 (1933). (4) H. Falkenhagen, M. Leist and
G . Kelbg, Ann. Phrsik, [6] 1 1 , 5 1 (1952); H. Falkenhagen and M. Leist, Naturwies., 41, 670 (1954); R. M. FUOSE and L. Onsager, Proc. Nall. Acad. Sci., U.S., 4 1 , 2 7 4 (1955). (Fj) 8 . F . Wishaw und R. H. Stokes, J . Am. Chem. Soc.. 76, 1991 (1954).
but !ave results identical with the more convenient drying a t 400 Conductance water was redistilled through Pyrex glass from the laboratory distilled water supply and stored in polyethylene bottles; at equilibrium with the laboratory air it had a specific conductance of 1.2 X IO-e ohm-' cm.-l. Solutions were prepared by weight, usually in amounts of about 150 g. so that the final weight was within the capacity of an analytical balance. For occasional larger batches of solution, the salt8 were weighed on analytical halance and the final solution on a large balance of sensitivity -5 mg. The amount of salt taken was always such that its weight was determinable within 0.005%; where more dilute fiolutions were required, these were prepared by weight-dilution of more concentrated stocks. Vacuumcorrections were applied throughout, and the densities given in the International Critical Tables6 were used to compute the concentrations in moles per liter given in Tables I and 11. Conductance cells having cell constants from 0.5 to 80 cm.-' were employed. They were of Pyrex glass, the Elatinurn-to-Pyrex seals being rendered completely tight y a layer of "Araldite" thermosetting resin on the side remote from the solution. The electrode-leads were of silver, well separated from each other and from the cell filling tubes. The cells were calibrated a t 25" using the Jones and Bradshaw 1 , 0.1 and 0.01 D potassium chloride standards,a retaining the International ohm units in which these standards are expressed. The cells were used in an oil-thermostat controlled to better than f0.003' as indicated by R Beckmann thermometer; the actual temperature was thus constant within these limits throughout the work, but y a y have been a8 much as 0.02' different from the true 25 , this being the accuracy of the standard thermometer used. However, since the temperature coefficients for the solutions are very similar to those of the calibration standards, a negligible error should arke from this uncertainty. Two measuring bridges were used, the earlier one being built up from a calibrated post-office hox, while later a Leeds and Northrup Jones conductivity bridge became available. Both salts were studied with both
.
(6) "International Critical Tables," Vol. 111, McGraw-Hill Book Co., Ino.. New York, N . Y.
J. F. CHAMBERS, J. M. STOKESAND R. H. STOKES
986
bridges, the results (Table I) being in excellent agreement, thou,gh those from the Jones bridge are of somewhat higher precision. All measurements were made at 500,100 and 2000 c./s.
Vol. 60
graphs of deviation-functions of the form x = A d ; were prepared, where the constant A is arbitrarily chosen to make the range of variation of x only a few units of equivalent conductance. Results Suitable values were A = 20 for KC1 and A = 29 The experimental concentrations and equivalent for NaC1. These deviation functions are of course conductances are reported in Table I. Large-scale without theoretical significance. From the graphs, equivalent conductances at rounded concentrations TABLEI were obtained (Table 11). Errors in the tabulated E~UIVALEN CONDUCTANCES T OF POTASSIUM AND SODIUM values are unlikely t o exceed 0.03%. CHLORIDE SOLUTIONS AT 25" Comparison with Previous Results.-The data c = concn. of soln.; A = equiv. conductance. of Stearn,' after adjusting to the Jones and BradPotassium chloride Sodium chloride shaw standards, show considerable scatter about the A, Int. ohm-1 A, Int. ohm-' c, mole 1. - 1 mole-1 cm.9 c , mole 1.-' mole-' 0m.l present results. The results of Shedlovskys in the A. Results using P.O. box bridge (J.M.S. and R.H.S.) region 0.1M.22 N NaCl and 0.10-0.12 N KC1 are in good agreement with our results, and were in0.14075 126.64 0.15621 103.66 cluded in the deviation-function graphs from which ,19141 124.43 .20998 101.36 Table I1 was prepared. The standard values of ,28307 121.51 .24584 100.02 Jones and Bradshaw3 for 0.1 and 1demal potassium ,36417 119.71 .33998 97.29 chloride correspond to A = 128.96 for 0.099692 N 1,5329 108. 08 .49935 93.66 KC1 and A = 111.915 for 0.99488 N KC1, and were 2.0000 105.29 .68703 90.26 also used in preparing Table 11. 2.6082 101.72 1.05142 85.12 A
+
-
3.0645 3.6951 4.0000
99. 08 95.37 93.46
1.3948 1.5193 1.9279 2.3793 2.7439 3.1431 3.5037 4.5199 5.3540
81.02 79.65 75.41 71.14 67.82 64.36 61.30 53.13 46.83
B. Results using Jones bridge (J.F.C.) 0.12004 .14968 .18588 .24678 .32330 .40698 .53211 .66460 ,76142 .93485 1.1934 1.5642 1.9155 2.3789 2.6188 3.4686 3.7046
127.67 126.13 124.58 122.53 120.54 118.81 116.79 115.10 114.03 112.41 110.35 107.87 105.74 103.07 101.70 96.72 95,29
0.11300 .12452 .18776 ,26492 ,36091 .46914 .60766 ,66232 .74528 .86366 1.2312 1,4647 1.8416 2.6739 3.1723 3.8769 4.3281 4.8114
105.91 105.24 102.19 99.41 96.71 94.25 91.60 90.65 89.34 87.58 82.87 80.215 76.277 68.445 64.088 58.228 54.622 50.882
TABLE I1 EQUIVALENT CONDUCTANCES OF POTASSIUM AND SODIUM CHLORIDE SOLUTIONS AT ROUND CONCENTRATIONS AT 25" C
0.1 .125 .15 .175 .2 .25 .3 .4 .5 .6 .7
.8 .9
AKC~
128.96 127.40 126.11 125.01 124.08 122.43 121.09 118.96 117.27 115.88 114.69 113.65 112.72
AN~CI
106.74 105.21 103.92 102.74 101.71 99.89 98.37 95.77 93.62 91.73 90.04 88.51 87.09
.
c
1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.350
AKCI
'
111.87 110.30 108.92 107.64 106.43 105.23 102.38 99.46 96.54 93.46 ,.. ,
,.
.. .
AN~c~
85.76 83.26 80.95 78.77 76.70 74.71 70.02 65.57 61.33 57.23 53.28 49.46 46.86
Theoretical discussion of the results will be postponed until data for other salts and temperatures are obtained. Acknowledgment.-The results reported in Table IB were obtained by J. F. C. during the tenure of an Electrolytic Zinc Company Research Fellowship, for which our thanks are expressed. (7) A. E. Stearn, J. A m . Chem. Soc., 44, 670 (1922). (8) T. Shedlovsky, A. S. Brown and D. A. MacInnes, Trans. Electrochem. Xoc., 66, 165 (1934).
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