2137
Heats of Mixing of Aqueous Electrolytes G. Swain and D. F. Evans, ibid., 88, 383 (1966); (f) J . H. Jones, ibid., 6 7 , 855 (1945). (25) (a) D. F. Evans, J. Thomas, J. A. Nadas, and M. A. Matesich, J. Phys. Chem., 7 5 , 1714 (1971): (b) M. B. Reynolds and C. A. Kraus, J. Amer. Chem. Soc., 7 0 , 1709 (1948); (c) M. J. McDovell and C. A. Kraus, ibid., 7 3 , 3293 (1951). (26) R . Zwanzig, J. Chem. Phys., 38, 1603 (1963).
(27) D. F. Evans, J A . Nadas, and M. A. Matesich, J. Phys. Chem., 7 5 , 1708 (1971). (28) R. M. Fuoss, J. Amer. Chem. SOC.,80, 5059 (1958). (29) A. D. Buckingham, Discuss. FaradaySoc., 24,151 (1957). (30) W. R. Gilkerson,J. Chem. Phys., 25, 1199 (1956). (31) R. G. Pearson, J. Amer. Chem. SOC.,85, 3533 (1963). (32) R. G. Pearson, J. Amer. Chem. SOC.,89, 1827 (1967).
Heats of Mixing of Aqueous Electrolytes. X. Lithium Chloride with Cesium Chloride and Tetra-n-butylammonium Chloride with Potassium Chloride at Low Concentrations J. S. Falcone, Jr.,' A. S. Levine,2 and R.
H. Wood*
Department of Chemistry, University of Deiaware, Newark, Delaware 1971 7
(Received January 22, 19731
The heats of mixing of LiC1-CsC1 and n-Bu4NCl-KCl have been measured in water at 25" to low concentrations. These data have been used to test two predictions. (1) The prediction that a t low concentrations, RTho changes in the direction predicted by Friedman's higher order limiting law. ( 2 ) The prediction of Wen, Nara, and Wood that the heat of mixing Bu4N+ ion a t I = 1 m with any alkali metal ion in the presence of a common anion will be dominated by the heat effect of diluting the Bu4N+ ions. The experimental results are in agreement with both predictions.
Introduction The purpose of this paper is to present the results of the tests of two predictions of the behavior of heats of mixing symmetrical electrolytes. The first prediction is due to Friedman3 who used Mayer's cluster expansion for ionic solutions to show that the free energy of mixing at constant ionic strength will obey a higher order limiting law analogous to the Debye-Huckel limiting law. The theory predicts a similar limiting law for the heats of mixing and this is tested in the present paper. The second prediction, due to Wen, Nara, and Wood,4 is that the heat of mixing tetra-n-butylammonium chloride (Bu4NC1) with any alkali metal chloride a t 1 m should be roughly given by d,H/W = y ( 1 - y)F(-2300) cal/kg of solvent. This is a semiquantitative prediction because i t is based on earlier evidence that indicated that the interactions of tetrabutylammonium ions with each other are so large that other ion-ion interactions are negligible. The prediction is based on the heat of diluting tetrabutylammonium chloride with water which is another measure of the interactions of tetrabutylammonium ions with each other. The present results give supporting evidence to the higher order limiting law derived by Friedman3 and show that the prediction of the heat of mixing tetrabutylammonium chloride with potassium chloride was within 12% of the actual valu(e. Experimental Section Cesium chloride (99.9%) was obtained from ROC/RIC5 and was used without further purification. Lithium chlo-
ride was obtained from Fischer and after drying was analyzed for C1- using AgN03 and a dichlorofluorescein indicator and was assayed a t 98.7%. After recrystallization from absolute ethanol and drying in a vacuum oven, this salt assayed at 99.8%. Certified ACS grade KC1 was dried in a vacuum oven a t 100" €or several hours. The tetrabutylammonium chloride was obtained from Eastman Organic Chemicals and it was purified by precipitation three times from spectral grade acetone with the use of cold anhydrous ether. The crystals were dried in uucuo a t room temperature for 24 hr. After pulverizations they were then dried 48 hr in uacuo at 50". Potentiometric titrations with AgN03 employing a AglAgCl electrode revealed a purity of 99.4%. Karl Fischer titration indicated that 0.3% of the impurity was due to HzO. These salts were used to prepare approximately 1 m stock solutions. The pH values were KC1, 6.0; Bu4NC1, 5.3; LiC1, 8.3; CsC1, 5.6, respectively. The pH of the LiCl solution was adjusted to the value 5.6 by the addition of HC1 (
