ROBERT w.KUNZEAND R.4YMOND h!!.FUOSS
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CONDUCTANCE OF THE ALKALI HALIDES. VI. RUBIDIUM CHLORIDE I S DIOXANE-WATER MIXTURES1*2 BYROBERT W.KUNZEAND RAYMOND M. Fuoss Contribution h'o. 17IW from the Sterling Chemistry Laboratory of Yale University, New Haven, Connecticut Received November I,1962 The conductance of rubidium chloride a t 25' has been measured in dioxane-water mixtures covering the range of dielectric constant 11.88 6 D 6 78.54. The limiting conductance of the salt in water is 153.57 f 0.02 which gives 77.20 for the single ion conductance of rubidium. The contact distance &J in water is 3.02; it increases to 7.56 a t D = 11.88. Like the other alkali halides in dioxane-water mixtures, U K and a h also vary with dielectric constant. The sequence of association constants at a given dielectric constant is K A (RbCI) > K A (KC1) > K.4 (NaCl).
We present in this paper conductance data for dilute solutions of rubidium chloride in dioxane-water mixtures, covering the range 11.88 D 78.54 in dielectric constant. All symbols are defined in the previous paper3 of this series.
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Ka(KC1)'l > K.4(iYaCl),3 that is, the largest lattice ion gives the highest amount of ion pairs a t a given value of D. Similar reversals of the sequence expected on the basis of simple electrostatics, and lattice radii are reported : Fratielli16 finds KA(CSC1) > KA(KCI)in ethanol-water mixtures, and Gordon's datal7 for salts in ethanol give Ka(KC1) = 85, KAjNaC1) = 34, and KA(LiC1) = 16. (13) 5. E. Lind, Jr., and R. AI, F U O ~J B . Phys. , Chem., 66, 1727 (1962). (14) E. Grunwald, private communication. ( 1 3 17. Sutherland, Phil. Mag., 9, 781 (1905). (16) A. Fratielli, Thesis, Brown University, 1962. (17) J. R. Graham, G. S. Kell, and A. R. Gordon, J . Am. Chem. Soc., 79, 2352 (1957).
SOLUBILITY RELATIONS OF THE ISORIERIC TRICHLOROTRIFLUOROETHAn'ES BY H. HIRAOKA AiVD J. H. HILDEBRAXD Department of Chemistry, University of Califcmia, Berkeley, California Received November 14,1961 Solvent properties of CCl.F.CCIF2 (A) and CC13.CF3 (B) have been determined and compared, with the following results: Vapor pressures a t 25' are: A, 361.1 mm.; B, 363.6 mm. Their variations with temperature yield the molal heats of vaporization: A, 6.86 kcal., B, 7.24 kcal., and the solubility parameters: A, 7.25; B, 7.46. Their partial vapor pressures over mixtures with (CAFg)& correlate closely with the respective solubility parama t 25". This and the previously found solubility in A likeeters. The solubility of iodine in B is 0.283 mole 70 wise agree closely with solubility parameters. h graphic representation of all available solubilities of iodine in violet solutions, paraf'iin solvents excepted, s h o w excellent correlation with the equation, In uZh = In 2 2 ~291~(a2 - a1)2/RTwith the activity of solid iodine, ass = 0.256, v:, = 58.5 cc., and 82 = 14.1. 91 is the volume fraction of the solvent.
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Smith, Walkley, and Hildebrand' found the partial molal volume of bromine in c-C4ClZF6to he 64.3 cc.. but that iii a mixture containing 0.6 mole % CCl, it had fallen to 54 cc., its value in pure CC1,. This suggested that in the "freon" CCl3.CF3not only iodine but also a non-polar fluoride might find the environment more friendly than in its isomer, CCl2F.CC1F2. I n any event, a comparison of these two solvents seemed well worth making. Experimental The CCll. CF- was aupplied by du Pont through the kindness of Dr. C. L. Hobbs. I t was used without further purification, (1) E. B. Smith, J . Walkley, and J . H. Hildebrand, J . Phys. Chem., 63,703
(1959).
since its only significant impurity \vas claimed t o be abolit 1% of the other isomer. The CCLF.CC1FLwa8 a product of Allied Chemical and Dye Co.: the (C,Fo),N was from Minnesota Mining and Manufacturing Co. The two latter compounds were distilled. The two freons were degassed by repeated freezing and melting under vacuum. Vapor pressures were measured in a simple isoteniscopic apparatus. In the case of the mixtures with the perfluoroamine, compositions %eredetermined by the weights of the components, correcting for the weight of freon in the vapor phase. The solubility of iodine in CC1,. CFJ was determined from the extinction coefficient of the visible band, standardized by the extinction of solutions of lrnuwn composition.
Results Tahle I gives the observed vapor pressures of the two compounds. Plots of log p vs. 1/T, show straight lilies
