C. H. BRUBAKER, JR.,AND T. E. HAAS
866
actions can be treated separately. It appears from our data that trimethylpyrazine would have a pK1 of 2.8 and a pKz of - 3 . 5 . Acknowledgments.-This work was supported
Vol. 65
by the Graduate Council of Southern Illinois Uiiiversity. We are also indebted to the Wyandotte Chemicals Corporation for generous samples of the pyrazines used.
T H E ACTIVITY COEFFICIESTS OF AQUEOUS SOLUTIONS OF TRIS- (ETHYLEXEDIAMIXE)-COBALT(III) PERCHLOR-4TE BY C. H. BRUBAKER, JR., AXD T. E. Haks Kcdzze Chemical Laboratory, Mtchtgan Slate Unwerszfy,East Lansang, Jlzchigan Receired Drcrniber I ? , I960
Activity and osmotic coefficients of solutions of Co(en)3(C104)3have been determined a t 25” b:- isopiestic coniparison nith KCl solutions. Measurements have been made from about 0.04 to 0.5404 m (saturation), This salt is similar in behavior to other complex 3-1 salts, but some differences are found.
In a series of recent papers,’ we have given the activity coefficients of a dozen complexes, which were high charge electrolyt’es (1-2, 3-1, 1-3, 3-2, 1-4 and 4-1). To complete the 3-1 series, we now have determined the activity coefficients of tris(ethylenediamine)-cohalt (111)perchlorat.e, Co(eii)3(C104)3 . Experimental The apparatus and experimental procedure are those previously $escl;!bed Co( en)sCla was prepared by the procedure in Inorganic Syntheses.”2 Co(en)$( then wis prepared by quantitative metathesis between the chloride and an .4gC104 solntion, as had been done for the tris-(propylenediamine)-cobalt(II1) perchlorate and other perchlorat,es we have ~ t u d i e d . ~The salt was recrystallized three times from demineralized, distilled water and the hydrate, thus obtained, was dried a t 100’ until the anhydrous form was obtained.
+
(1 - $ ) o s ~ c = 0.i676sm(i)umt’%
‘/$til
-
(Arbp,slriuc,thcd
(1)
The notation is that of Hariied and On-eii4 and (Ab) smoothed was determined by the method of Scatchard and P r e n t i ~ s . ~In order to obtain the best agreeme$ with experiment (Table I), ii was taken as 4.7 A. and B = 1.33. The B is positive and d is somewhat larger than for Co(en)3C13or Co(pn)3(C104)3,which were 3.4 and 3.5, respectively. It was possible to fit the data for lower concentrations with d = 4.0 and B = 0.9, but only up to m = 0.2 and then the fit was also poorer below 0.08 m. Thus the higher d seems preferable. -4ctivity coefficients were calculated hy tEc method of Smith,6i.e.
Results and Discussion i2 ) I n Table I are shown the experimental molalit,ies up to m = 0.2755 and then were ohtained from 7n = and osmot’ic coefficients. The maximum concen0.2755 to saturation by graphical integration of tration of 0.5404 m is for the sat,urat*edsolutiori. TABLE I ISOPIESTICLIOLALITIES, OBSERVED AXD CllLCULATEU OSMOTIC COEFFICIENTS O F Co(eil)d(CIOr)a 24.978 f 0.005° nz
ohsd.
0.04268 ,05223 ,08421 ,121s ,1474 1879 1902 .26i8 .275*5 ,3474
0 . 7342 ,7163 6624 ,6392 ,652
