320
0. D. BONNER AND LINDALou SMITH
Vol. 61
A SELECTIVITY SCALE FOR SOME DIVALENT CATIONS ON DOWEX 50 BY 0. D. HONNERAND LINDALou SMITH^^^
.
Dept. of Chemistril, University of South Carolina, Columbia, Soiilh Carolina Received Septembdr 10, 1066
Equilibrium studies involvin cu ric, zinc, cobaltous, nickel, magnesium, cadmium, uranyl and lead ions on Dowex 50 resins of a proximately 4 8 a n t 1 6 4 divinylbenzene content have been made at a constant ionic strength of approximately 0.1 M. &ese ions in addition to barium, strontium and calcium ions have been included in the same selectivity scale as the common univalent cations. Activity coefficient corrections hhve been made for the ions in the aqueous solution phase, and these corrections have been substantiated in some instances by the results of exchange reactions carried out at lower ionic strengths. I t is observed that the order of decreasing activity coefficients for the nitrates of both the univalent and the divalent ions is the same as that of the selectivity scale. The characteristic maximum water uptake of the resin in these ionic forms is reported,
A summary of the results of ion-exchange equilib- the resin and solution phases cannot be determined directly. A ueous solutions of known compositions were passed over ria and maximum water uptake of Dowex 50 res- columns of resin until equilibrium was reached. Since the ins of 4, 8 and 16% DVB content involving the uranyl ion interferes with acid-base titrations, the hydrogen common univalent cations has been reported previ- ion in the resin phase was then calculated as the difference ously.a The results of ion-exchange equilibria in- between the capacity of the resin and the uranyl ion found. volving the four divalent cations cupric, barium, Discussion and Results strontium and calcium also have been r e p ~ r t e d . ~ It has been indicated4 previously that if exAll of these exchange reactions were carried out a t an aqueous solution ionic strength of approximately changes between univalent and divalent ions or 0.1 M. The activity coefficient ratio term for the between two divalent ions are represented by equaions in the aqueous solution which appears in the tions of the type 1/2MXn BRes 1/2MRes2 BX (1) expression for the equilibrium constant was ignored, although it was realized that it might dif- and fer from unity by as much as 20% in some ex'/aMXz l/2QReaz = l/zMResz '/aQXz (2) change~.~ Experimental data on exchanges involving seven they are directly comparable with exchanges beadditional divalent ions are reported herewith. An tween univalent ions which are represented by the activity coefficient correction is made for these as equation well as for all previously calculated equilibrium AX + BRes = ARes BX (3) constants. This permits the establishment of a single selectivity scale which includes the nine uni- The equilibrium constantfl for the above reactions valent ions and the 11 divalent ions studied up t o are N'/'MRea)mBXf/aMResry2Bx~ = fl/zUILoasYaBX this time. Kl.2 = . (4 1 NBResm'/aMXrfBReaY'/'MXc f BReiY"/'UXz Experimental
+
-
+
+
+
+
The methods of equilibration and separation of aqueous and resin phases have been described previously.' In preparation for analysis the resin phase was first washed free of adhering electrolyte and then exhaustively eluted with an electrolyte which would not interfere with the analysis for the ions in question. Aliquots of this effluent and also of the solution hase were then analyzed for both ions being exchanged. 8obalt and zinc ion concentrations were determined radiometrically, Cow and Znos bein used as tracers. Nickel ion concentration was determined f y titration with standard potassium cyanide solution. Lead and cadmium ion concentrations were determined by complexometric titration with the disodium salt of ethylenediaminetetraacetic acid in acidic media, PAN serving as indicator. Calcium and magnesium ion concentrations were determined by a similar titration in ammoniacal solution. copper ion concentrations were determined either by complexometric titration with standard disodium EDTA in acidic media, by titration of the iodine liberated by cupric ion from an excess of acidified potassium iodide solution wlth standard thiosulfatc solution, or by electrolytic deposition of copper on weighed platinum electrodes. Uranyl ion concentrations were determined by reduction of the uranium from the 7t6 to the +4 state in a Jones reductor and subsequent titration with standard dichromate solution. The uranyl-hydrogen exchange is the only one studied in which both ions in both (1) Theae reaiilts were developed under a project sponsored by the United States Atomic Energy Commiaaion. (2) Part of thu work described herein was included in a thcsia submitted by Linda Lou Smith to the University of South Carolina in partial fulfillment of t h e requirements for the degree of Master of Scienoe. (8) 0. D. Bonner, THIE JOURNAL, 69, 719 (1966). (4) 0. D. Bonner snd Frances L. Livingston, ibid., 60,630 (1966).
and NAResmBXfARedrg k . f . ~ ~ d r s ~(a)x NBRdTZAXfBRedAx f f respectively, where m is the aqueous phase molaJK1'l
ity, N is the molar fraction of the ion in the rePin phase, f is the activity coefficient of the resinate, y is the mean activity coefficient of the electrolyte in the aqueous phase and IC is the quantity later referred to as the equilibrium quotient. When the exchange reactions are represented in this manner, triangular comparisons may be obtained by addit,ion or subtraction of two equations to yield a third, and the resultant equilibrium constant for the third reaction will be the product or quotient of the first two constants. This logarithmic additivity of equilibrium constants has also permitted the establishment of a quantit'ative selectivity scale3 for the conimon univalent ions by the arbitrary assignment of a value of unity for the affinity of each resin sample for lithium ion. The equilibrium constant for each exchange reaction has been calculated from the equation6 (6) W . J. Argersinger, A. W. Davidson and 0. D. Bonner, Trans. Kans. A d . Sci.. 68, 404 (1860).
SELECTIVITY SCALE FOR DIVALENT CATIONS ON DOWEX 50
March, 1957 log K =
Jollog k dX
(7)
where X is the equivalent fraction of the preferred ion in the resin phase. Activity Coeficient Corrections.-It has been realized that the K values calculated in this manner are in errora because the activity coefficient ratios of the ions in the aqueous solution were assumed to be unity. This assumption was made because few activity coefficient values are available for mixed electrolytes at an ionic strength of 0.1. The error in K caused by neglect of solution phase activity coefficients becomes appreciably larger, however, in exchanges involving divalent ions than was the case for univalent ion exchanges, and a correction becomes necessary. This correction may be made by application of the ionic strength principle and use of the activity coefficients for the electrolytes in pure solutions at an ionic strength of 0.1.. Although this procedure probably does not completely eliminate the error, it reduces it considerably. As an example the activity co~ ~ be cited. The efficient ratio Y H N O ~ / Y A ~ Nmay value of this ratio' for pure solutions of nitric acid and silver nitrate may be calculated to be 1.078 for 0.1 M solutions. The value in mixed solutions8 is nearly constant for all ratios of nitric acid to silver nitrate, and has an average value of 1.060. Since one of the ions involved is silver ion, the difference in the activity coefficient ratio for pure and mixed solutions observed here is probably as great as will be encountered in most systems. A slightly greater refinement in this correction might be made by use of the interaction coefficients of Guggenheim.g.la This was not done, however, because these coefficients are not known for all of the univalent electrolytes which were studied, and only for barium ion of the divalent ions studied. The calculated values of the activity coefficient correction term for these exchanges range from 1.016 for the hydrogen-lithium system to 1.280 for the cupric-hydrogen system in chloride media. These activity coefficient corrections have been verified in several instances by the study of exchanges at several lower ionic strengths, extrapolation of the k values to infinite dilution, and comparison with the value of k calculated from exchanges at the ionic strength of 0.1 M to which the activity coefficient correction had been made. Examples of these comparisons are given in Table I. The calculated activity coefficient correction factor for almost all of the systems was greater than unity, the calcium-cupric exchange constituting one of the few exceptions. There is a very large correction in thc case of the magnesium-hydrogen exchange even at, an ionic strength of 0.01. This is to he expected because of the differences in the rate (6) Oscar (1953).
D. Bonner and Vickers Rhett, T H IJOURNAL, ~ 67, 254
(7) R. A. Robinson and R . H. Stokes, Trans. Faraday Soc., 46, 612 (1949).
(8) 0. D. Bonnor, A. W. Davidson and W. J. Argersinyer, J . Am. Chem. Soc., 74, 1047 (1952). (9) E. A. Guggenheim,, "Thermodynamics," Interscience Publishers, Inc., Now York, N. Y..1949, p. 315. (10) E. A. Cuggonheim and J. C.Turgeon, Trans. Faradizy Soc., 61, 747 (1955).
327
20 40 60 80 100 Mole ?L ," calcium resin. Fig. 1.-Calcium-cadmium exchange: A, 16% DVB; B, 8% DVB; C, 4% DVB. 2.4
2.2 6
z8g 2.0 g
*e
1.8
w 1.6
1.4 40 60 80 100 Mole % lead resin. Fig. 2.-Lead-calcium exchange: A, 16% DVB; B, 8% DVB; C, 4% DVB. 20
40 60 80 100 Mole yo cupric resin. Fig. 3.-Cupric-magnesium exchan e: A, 16% DVB; B, 8% DVB; C, 4% b V B . 20
of change of the activity coefficients with concentration between 1,t and 2,l electrolytes in very dilute solutions. Selectivity Data.-The experimental data for the new exchange systems studied are presented graphically in Figs. 1-8 as plots of the equilibrium quotient, k, as a function of resin loading. The value of k does not change markedly with resin loading for many of the divalent ion exchanges studied. The lead-calcium exchange is interesting in that k increases with increased lead (the preferred ion) loading. It is more common for k to decrease with an increase in the resin content of
0.D. BONNER AND LINDALou SMITH
328 1.4
2.0
1.2
4 1.8
Vol. 61
c;
8
+
.-I
8 %a 6 $ 1.6
w
.% 1.0 .C
3
'C
w"
3 0.8
20
40 60 80 100 Mole % cupric resin. Fig. 4.-Cupric-zinc exchange: A 16% DVB; B, 8% DVB; c, 4% DGB.
1.4
1.2
40 60 80 100 Equiv. yo uranyl resin. Fig. 8.-Uranyl-hydro en exchange: A, 16% DVB; 'B, 8% D%B; c, 4% DVB.
20
1.2 a
.CI
s 3 1.0 6
TABLE I EQUILIBRIUM QUOTIENT VARIATION WITH IONIC STRENQTK
'c: P
g
-
;T 0.8 40
20
80
80
100
Mole % ' cobalt resin. Fig. 5.-Cobalt-cu ric exchan e: A, 4% DVB; B, 8% h 3 ; C, 1 0 5 DVB. 4 1.2 8 '3
Ex-
ohange
0.1
0.07
ion
0.01
0.001
0.0,
0.0"
k at arbitrary reah loading
Ca-Cd 54.2 1.25 1 , 3 3 1.31 1.28 50.5 1.40 1.36 1.34 1.32 Ca-Cu Mg-H 87.5 1.07 1.70 1.74 2.00 Pb-Ca 76.1 1.78 1.80 1.83 1.94 Calculated by the application of solution haae activity coefficient corrections to exohangee performet a t 0.1. b Extrapolated valuee. 0 Activity coefficient of $b(NO& not known, d Extrapolation uncertain.
-
s
6
8 1.0 'E:
P
s w"
Re"& loading % PI* ferred
(8% DVB resin)
TABLE I1 0.8
40 60 80 100 Mole % nickel resin. ric exchange: A, 4% DVB; B, 8% bVB; C, 16% DVB.
20 Fig. B.-Nickel-cu
3.0
2.5
'
REVISEDSELECTIVITY SCALEFOR UNIVALENT IONSON DOWEX 50 4%DVB
Li H Ne "4
K Rb Ca Ag T1
1.oo 1.32 1.58 1.90 2.27 2.46 2.67 4.73 6.71
8%DVB
16% DVB
1.oo 1.27 1.98 2.55 2.90 3.16 3.25 8.51 12.4
1.oo 1.47 2.37 3.34 4.50 4.62 4.66 22.9 28.5
4
the preferred ion, although there are several instances where k passes through a maximum or a s minimum value. The nickel-cupric system is unusual in that nickel ion is preferred to cupric ion on .-3 the 4 and 8% DVB resins, while cupric ion is preferred on the 16% DVB resin. A selectivity scale for nine of the univalent ions, ;T which has been revised by the correction for solution phase activity coefficients, is given in Table 11. 1.o A similar selectivity scale for eleven divalent ions is given in Table 111. Both scales are based upon the arbitrary assignment of the value of unity to affinity of lithium ion for each resin. Four univalent0.5 0 20 40 60 80 100 divalent ion exchange systems provide the data for comparison of univalent and divalent ion affinities Equiv. % magnesium resin. Fig. 7.-Magnesinm-hvdrogen exchan e: A, 16% DVB; in these tables, namely, the cupric-hydrogen and silver-cupric systems, which have been reported B, 875 DVB; C, 4% D t B . .9
i; 2.0
March, 1957
PERFLUOROTRI-R-BUTY LAMINE-2,2,4-TRIMETHYLPENTANE-r\TITROETHANE
329
pr~viously,~ and the cupric-magnesium and magnesium-hydrogen systems.
ity coefficients’J1 for all of the univalent and divalent ions for which such activity coefficient data are available. TABLE I11 Swelling Data.-The data representing the maxiSELECTIVITY SCALEFOR DIVALENT IONS ON DOWEX 50 mum water uptake of the 4,s and 16% DVB resins 4 % DVB 8% DVB 16% DVB in the various divalent ionic forms are presented 2.45 3.34 uo2 2.36 in Table IV. Similar moisture data for the uniMg 2.95 3.29 3.51 valent cations8 closely follow the order of the Zn 3.13 3.47 3.78 selectivity scale in that the ions which cause the co 3.23 3.74 3.81 resin to swell the most are the least preferred. cu 3.29 3.85 4.46 This is not so generally true for divalent cations, Cd 3.37 3.88 4.95 except for the 4% DVB resin. There are two Ni 3.45 3.93 4.06 possible reasons for this. The error in these moisCa 4.15 5.16 7.27 ture uptake data is probably of the order of *2%, Sr 4.70 6.51 10.1 and this uncertainty in several instances could rePb 6.56 9.91 18.0 verse the positions of the ions in the moisture upBa 7.47 11.5 20.8 take table. Also, it is not a thermodynamic necesTABLE IV sity that the resin imbibe more solvent in the less MAXIMUM WATERUPTAKE OF DOWEX 50 REBINSIN VARIOUS preferred form. If the osmotic pressure effect and IONICFORMS (g./equiv.) the solution phase activity coefficients are ignored, 4% DVB 8% DVB 16% DVB the equation for the equilibrium quotient is12 UOn MK
Zn co cu Cd Ni Ca
Sr Pb
Ba
339 315 3 13 306 303 313 298 282 250 203 167
167 175 178 177 173 166 157 159 153 130 122
121 129 127 129 124 117 118 115 113 106 97
It is interesting to compare the above selectivity scales with values of the activity coefficients of salts of these ions. If one chooses the nitrates, which are similar to the sulfonates in that they are large oxygenated anions with a somewhat diffuse negative charge, the order of the selectivity scale is exactly the same as the order of decreasing activ-
THE
TERNARY
where BRes refers to the resin containing B+, the preferred ion. The water uptake of the resin equals 1000/m). The data for the xolution of this equation are, of course, not obtainable experimentally, since the swelling of the resin is limited by its cross-linking and the state of infinite dilution can never be reached. The equation does illustrate, however, that it is the value of the integral and not the value of ( l / m ~ ~-, I / ~ B R , ) for the wet swollen cross-linked resins which must be positive. (11) H. 5. Harned and B. B. Owen, “The Physical Chemiatry of Electrolytic Solutions,” Reinhold Publ. Corp., New York, N. Y., 1960, pp. 567, 002. (12) 0. D. Bonner, V. F. Holland and Linda Lou Smith, THIS JOURNAL, 60, 1102 (1856).
SYSTEM : PERFLUOROTRI-TZ-BUTYLAMINE-!~,Q,~-TRI METHYLPENTANE-NITROETHANE BY JAYVREELAND~ AND ROBERT DUNLAP Department of Chemistry, University of Maine, Orono, Maine Received September 19, 1066
The mutual solubilities of 2,2 Ptrimethylpentane with perfluorotri+butylamine and with nitroethane were determined. The ternary system composed of these substances, studied at six tem eratures between 25 and 51.3’, is the first ternary system to be re orted with a fluorocarbon as one of the components. $he existence of three liquid phases above the temperature at whici two of the components become completely miscible is a novel phenomenon. The study demonstrates exactly what happens to the phase boundaries of the internal triangle in the phase diagrams as the temperature is increased to 34.8”, the highest. temperature at which three liquid phases are stable. The roperties of the ternary system are in accord with the theory of regular solutions when compared with the properties of the tinary systems, but not when compared with thermodynamic properties of the pure components.
Hildebrand has used the solubility parameter,a 6, the square root of the internal pressure, as a meas(1) Presented before the 120th Meeting of the American Chemiaal Society, New York City, September, 1954. (2) Submitted as a thesis in partial firlfillment of the requirements of the Bachelor of Science dearcr! in Chemistry at the University of Maine. (2) J. H. Hildebrand and R . 1,. Rrott, “Solubility of Nonelectrolytea,” Reinhold I’ubl. Corp., Now York, N . Y., 1950, pp. 129, 423.
ure of solvent power. I n general, the larger the difference in 6 values for two particular substances the lower their mutual solubility. The magnitude of these parameters ranges from 6 = 7 (cd’’2 cm.-’’Z) for hydrocarbons to 6 = 24 for water. I n contrast to all other organic liquids which have higher parameters than tlhe hydrocarbons, the fluorocarbons have 6 values near G. The mutual
