RILVER ACETATE AS AN AMPHOTERIC BASE
1299
,4 method is described for measurements with Sas, G I 4 , and Ca4s.Results of measurements of the surface adsorption of hexadecyl sodium sulfate and calcium ions as “impurities” in dodecyl sodium sulfate are given and discussed.
The author wishes to thank Professor Ole Lamm for his encouragement and interest in this work, Mr. T. Vestermark and Dr. E. Stenhagen for valuable discussions, and Mr. E. Lindberg and Mr. I. Andersson for their assistance in the experimental part of the work. The work was supported by the Swedish Atomic Committee. REFERENCES (1) ANIANSSON, G . , AND LAMM, OLE: Nature 166, 357 (1950).D
( 2 ) DIXON, J. K., WEITH,A. J., JR.,ARGYLE, A , , AND SALLY, D . J . : Nature 163,845 (1949). (3) HUTCHINSON, E . : J. Colloid Sci. 3, 413 (1948). (4) HUTCHINSON, E . : J. Colloid Sci. 4, 600 (1949). (5) LIBBY,W . F.:Anal. Chem. 19, 1 (1947). (6)MILES,G.D . , AND SHEDLOVSKY, L.: J . Phys. Chem. 48, 57 (1944). (7) REICHENBERG, D . : Trans. Faraday SOC.49, 467 (1947). (8) SHEDLOVBHY, L.,AND Ross, J.: J. Colloid Sci. 4, 25 (1949). (9) Nucleonics 4. 84 (1949).
* A figure 2 is missing in two of the formulas, which should read:
ap
=
2RT(a In c
+ a In f)
and
rp---1
aY
2RT a In c
SILVER ACETATE AS AN AMPHOTERIC BASE SIGFRED PETERSON
AND
EDWARD K. DIENES
Chemistry Department, College of Arts and Sciences, University of Louisville, Louisville, Kentucky Received August 14, 1960
The demonstrated existence of Ag(C*H30& in aqueous solutions (7, 8) suggests its existence in solutions in acetic acid as the anion of amphoteric silver acetate. Davidson (1) has noted the enhancement by ammonium acetate of the solubility of silver chloride in acetic acid, but has interpreted this as an analogy to the action of ammonium hydroxide in aqueous solution. However, a similar interpretation of the solubility of cupric acetate in ammonium acetate solutions at room temperature is’refuted by occurrence of the same behavior upon substitution of potassium acetate for ammonium acetate (2). It is then of interest to investigate whether potassium acetate markedly increases the solubility of silver acetate in acetic acid.
1300
SIGFRED PETERSON AND EDWARD K. DIENES EXPBRIMENTAL
T o acetic acid of reagent quality of 99.5 per cent assay was added c. P. acetic anhydride equivalent to an assumed 0.5 per cent water. After mixing, the acid was kept for 2 weeks before use. The possible small excess of either water or acetic anhydride present should have little effect on the measured solubilities and no effect on our conclusions. Potassium acetate of reagent quality was dried a t 180°C. to constant weight. A commercial preparation of silver acetate was found (by titration with thiocyanate) to contain 62.94 per cent silver (theoretical, 63.16 per cent) and was used without further purification. In each solubility determination an excess of silver acetate was added to known weights of acetic acid and potassium acetate in a brown glass-stoppered bottle. The mixture was sealed with paraffin wax, immersed for at least 2 weeks in a thermostated water bath at 25.00"C. =k 0.05",and shaken at intervals during equilibration. Immediately upon removal of the bottle from the thermostat, samples of the liquid were removed by pipetting through a glass wool plug, weighed, and analyzed for silver by titration with potassium thiocyanate solution which had been standardized against fused silver nitrate. One solution was saturated in the above fashion with both silver acetate and potassium acetate. This was analyzed for potassium by precipitating the potassium and silver simultaneously with c. P. concentrated sulfuric acid [sulfates of both metals are quite insoluble in acetic acid (l)], collecting on a sinteredglass filter, washing the precipitate with acetic acid, drying at 180°C. for 2 hr., cooling over calcium chloride, weighing, and subtracting the weight of silver sulfate calculated from the volumetric silver determination on a sample of the same solution. RESULTS AND DISCUSSION
The compositions of the solutions saturated with silver acetate are shown in figure 1, calculated as mole per cent assuming that all the potassium acetate is in the liquid phase. Point S is the composition found for the solution saturated with both potassium acetate and silver acetate. It can be seen that the rise in solubility abruptly ends a t a potassium acetate mole fraction of about 5.5 per cent and remains constant (within experimental error) with further increase in potassium acetate. Consideration of the phase rule forces the conclusion that above 5.5 mole per cent potassium acetate the solutions are in equilibrium with two solid phases. The second solid phase cannot be potassium acetate. According to the data of Davidson and McAllister (3), acetic acid at 25'C. should be saturated with KCzHaOz.2HCzHaOz a t a mole fraction of 12.3 per cent potassium acetate; this does not differ greatly from our value of 11.55 per cent in saturated silver acetate (point S, figure l), considering that the latter is in a slightly different medium and that the value is based on an untested analytical method. The obvious conclusion is that a double or complex salt is formed between the two metal
SILVER ACETATE AS AN AMPHOTERIC BASE
1301
acetates; this was confirmed by a strong qualitative test for potassium (by precipitation with perchloric acid) in the solid residue from the solution indicated by X in figure 1. This complex is probably solvated, since mixtures of potassium and silver acetates take up considerable acetic acid before forming a liquid phase. A number of analogous solvated compounds between heavy metal and alkali acetates in equilibrium with acetic acid solutions have been reported (2, 4, 5). The dissolved silver probably exists as unionized AgA (A = acetate) and AgA;; Ag' can be neglected, since Kolthoff and Willman (6) 6nd silver acetate
I
I
I
2.0
4.0
I
I
I
8.0 10.0 MOLE PER CENT POTASSIUM ACETATE 6.0
FIG.1. Effect of potassium acetate on the solubility of eilver acetate in acetic acid
very slightly dissociated in acetic acid. If cAgis the analytical silver concentration and parentheses denote concentrations of the species of the enclosed formula, neglect of activity coefficients leads to the expression
+
c.u/(AgA) = 1 (A-)/K where K is the equilibrium constant for the reaction: AgA; = AgA AThe change in solubility of AgA with added KA before the limiting valueis reached is accounted for by a value of K = 0.04,assuming that (AgA) is constant and equal to the mole fraction of AgA in the saturated solution without KA, cAs is the analytical mole fraction of AgA, and (A-) is equal to the mole fraction of KA in the solution. In aqueous solution the same K is 0.023, obtained by converting to mole fraction basis the Kz/Ki of MacDougall and Peterson (8).
+
CONCLUSIONS
Potassium acetate up to a mole fraction of 0.055 incresses the solubility of silver acetate in acetic acid to an extent which can be accounted for by the
1302
JAMES HOLMES AND G. A. MILLS
formation of Ag(CIH302); with about the same stability which it has in aqueous solution. Above a potassium acetate mole fraction of 0.055 the solubility of silver acetate is constant, suggesting the existence of a solvated double or complex salt, potassium silver acetate. (1) (2) (3) (4) (5)
(6) (7) (8)
REFERENCES DAVIDSON: J. Am. Chem. SOC. 60, 1890 (1928). DAVIDSON AND GRISWOLD: J. Am. Chem. 800. 67, 423 (1935). DAVIDSON AND MCALLISTER: J. Am. Chem. SOC. 62, 507 (1930). DAVIDSON AND MCALLISTER: J. Am. Chem. Boo. 62, 519 (1930). GRISWOLD AND VAN HORNE: J. Am. Chem. soc. 67. 763 (1945). KOLTHOFF AND WILLMAN: J. Am. Chem. SOC. 66, 1014 (1934). LEDEN:Svensk Kem. Tid. 68, 129 (1946). MACDOUGALL A N D PETERSON: J. Phys. & Colloid Chem. 61, 1346 (1947).
AGING OF A BENTONITIC CRACKING CATALYST I N AIR OR STEAM' JAMES HOLMES* AND G. A. MILLS The Houdry Process Corporation, Linwood, Pennsylvania Received August 4 , 1960 INTRODUCTION
Since the original announcement of a commercial process for the catalytic cracking of petroleum in 1938 ( l l ) , widespread use has been made of an acidtreated clay as a catalyst for this purpose. It is of great practical importance that, with continued use, such a catalyst gradually declines in activity. This decline is believed due to changes in the catalyst brought about at the high temperatures encountered in the cyclic cracking-purging-regeneration operation. It has therefore become of considerable interest to understand the nature of the changes which are produced in the catalyst in relation to the loss of activity as a function of the high-temperature treatment received. It is recognized that the loss in activity depends not only upon changes of a physical nature, which occur to the porous structure, but also upon changes of a chemical nature, which alter the active surface of the catalyst. In the present paper, only the physical changes have been considered. Catalyst samples were calcined in an air or a steam atmosphere for fixed periods at a series of elevated temperatures, after which measurements of density, nitrogen adsorption, x-ray diffraction, and Presented before the Division of Colloid Chemistry at the 113th Meeting of the American Chemical Society, Chicago, Illinois, April, 1948. * Present address: Polychemicals Department, E. I. du Pont de Nemours & Company, Wilmington, Delaware.
