PATRICIA WHITEDOUMAUX AND ANDREW PATTERSON, JR.
3540
Liquid-Liquid Phase Separation in Alkali Metal-Ammonia Solutions. IV.
Sodium and Potassium
by Patricia White Doumaux and Andrew Patterson, Jr. Sterling Chemistry Laboratory, Yale University, New Haven, Connecticut 06620 Accepted and Transmitted by The Faraday Society
(February 20, 1967)
The phenomenon of liquid-liquid phase separation in ammonia solutions containing both sodium and potassium has been examined over a range of concentrations of both metals at two temperatures, -56.39 and -75.00'. Separate analyses were made for both metals with a precision of about 1%. Perceptible, but not large, metall-metalz interactions occur which cannot, from these experiments alone, be assigned with certainty solely to the rn-eta1atoms or to the positive ions.
In earlier papers's2 we have examined the effect on phase separation in sodium-ammonia solutions when metal salts are added. The results indicated that the effect of the salt depended upon its anionic constituent, and it seemed most likely (from other experimental measurements) that interactions between the electrons in the solution and the anion of a solvated ion-paired salt molecule were responsible for the observed broadening of the miscibility gap and raising of the consolute temperature. In spite of this a t least self-consistent interpretation of our data, the kinds of models for behavior of alkali metal-ammonia solutions which one invokes are not all in agreement and are often dependent upon the kind of experiment employed and the system studied. Thus, conductivity measurements on alkali metal salt-liquid ammonia systems by Hnizda and Kraus3 indicated a much smaller interaction of the halide ion with the solvent than is the case with the cation. On the other hand, Catterall and Symons4 have found the effect of the cation on esr g shifts in solutions containing both metal and salt to be greatly subsidiary to that of the anion of the salt used, as was also our finding in our phase separation measurements.1*2 M'hile these results are not necessarily in conflict-in one case salt only is present, while in the other both salt and metal are involved-and while it is likely that ion solvation was the important factor in Kraus' work but a quite different interaction responsible for the results in that of Catterall and Symons, we felt it desirable t o investigate the importance of possible The Journal of l'hysical Chemistry
metall-meta12 or metal ionrrnetal ion2 interactions on phase separation. We have done this through a study of phase separation in solutions containing both sodium and potassium. It is of interest that Professor Kraus, in his prefatory note to the "Colloque Weyl" presentat i o n ~ suggested ,~ just such an investigation. We plan to extend these measurements to other alkali metal systems.
Experimental Section The procedures used were essentially those earlier described.'n2 Total alkalinity was determined on the mixed metal hydroxide residues by titration with nitric acid. Potassium was determined in this solution remaining from the titration by a gravimetric procedure developed by I
