OSCARD. BONNXI~ AND VICKXESRHETT
254
ship holds only for adsorbed liquids having similar dipole moments and polarizabilities, considerable information on adhesion mechanisms can be gained from this approach. Obviously more data are needed to test its validity. It is conceivable, also, that the placement of the lines in Fig. 6 may be related to the concentration of polar sites on the solid surfaces, since the line for tin oxide with a higher concentration of ionic sites favorable to adsorption lies above that for untreated tin. The lowering of the free surface energy (7,)
Vol. 57
by a film adsorbed on the surface of a solid is the basis for the calculation of a fundamental quantity, the work of adhesion (WA). The values for W A given in Table I1 were calculated by the method of Jura and hark in^.^ Approximately four times as much work must be expended to separate liquid water from the surface of these solids as is needed to separate liquid heptane. The work required to separate water from these surfaces is about 2.5 times that necessary for the separation of propyl acetate or propyl alcohol.
EQUILIBRIUM STUDIES OF THE SILVER-SODIUM-HYDROGEN SYSTEM ON DOWEX 50 BY OSCARD. BONNER AND VICKERSRHETT~ lhpartinent of Chemistry of the University of South Carolina, Columbia, S. C . Received July d l , 1968
Equilibrium studies of the silver-hydrogen, silver-sodium and sodium-hydrogen exchanges on two samples of Dowex 50 have been made while maintaining a constant ionic strength of approximately 0.1 M . Comparison of these exchanges with another series of sodium-hydrogen exchanges, which have already been reported, shows a definite relationship between the selectivity of the resin and the maximum water uptake. The selectivity values and the selectivity-loading curves are discussed in the light of present theories.
Introduction It is known that when an ion exchange reaction occurs, selectivity is shown in nearly all instances. This is demonstrated by the fact that for a reaction such as A+
+ BR~B
=
B+
+A R ~ ~
the mass action equilibrium quotient is usually different from unity. It is also recognized that this equilibrium quotient is not constant for an exchange betnfeen two given ions but is a function of several variables, not all of which may be Some of the known variables are the capacity of the resin, the percentage divinyl benzene cross-linkage in the resin (as demonstrated by the maximum water uptake of the resin) and the percentage of each ion associated with the resin (ie., loading). There are no exact cation exchange equilibria data in the literature for a thoroughly charactekized resin. . Most of the.earlier work.was of an exploratory nature only. Recent investigators of ion exchange equilibria have reported only the equilibrium data and not the characteristics of the r e ~ i i i . Theoretical ~~~ interpretation of the ion exchange process and quantitative predictions of ion exchange selectivity have thus been very difficult. Experimental These data, which will be presented, represent six series of exchange reactions between three pairs of ions on two different resin samples. Equilibrium data on one resin sample (nominal 16% divinyl benzene) were obtained at Oak Ridge (1) Part of the work described herein was included in a thesis submitted by Vickers Rhett t o the University of South Carolina in partial fulfillment of the requirements for the degree of Master of Science. (2) G . E. Boyd, A n n . Reu. PILUS.Chem., 11, 309 (1951). (3) E. Hogfeldt, E. Ekedahl and L. G. Sillen, Acta Chem. Scand., 4, 1471 (1950). (4) 0. D. Boiiner, W. J. Argcrsinyer a i d A. W . Davidson, J. Am. C‘hsm. Soc., 14, 1044 (1952).
National Laboratory and on the second sample (nominal 8% divinyl benzene) at the University of South Carolina. Preparation of Resin Samples.-For the study of each exchange reaction two “pure” resins were prepared, one containing each of the cations involved in the exchange. The hydrogen form was prepared by passing 6 N hydrochloric acid through a column of the commercial product until the effluent gave no further flame test for sodium ion. For the preparation of pure silver resin, hydro en resin was placed in a column and silver nitrate passed %rough until the pH of the effluent showed no more than a negligible decrease from that of the influent. When radioactive methods of analysis were to be used a trace of AgllO isotope was added to the influent silver solution. A sample of the influent was retained in order to determine the activity per milliequivalent of silver ion. The pure sodium resin was obtained similarly by passing a solution of sodium chloride or sodium nitrate through a column containing pure hydrogen resin. When radioactive methods of analysis were to be used a trace of Na2‘ isotope was added to the influent solution. General Method.-In each exchange experiment, a weighed sample of the resin to be studied, of known moisture content, was placed in a ground glass stoppered flask in contact with an aqueous solution of the appropriate salts of the cations involved at a constant total ionic strength of 0.1 M . Equilibrium was hastened by agitation and was reached, in every case, withip two hours. The temperature was maintained a t 25 i 1 . Equilibrium Solution.-The concentration of each cation in the aqueous solution at equilibrium was determined by means of direct analysis; hydrogen ion by titration with standard sodium hydroxide solution; silver ion by potentiometric titration with standard potassium iodide solution or by measurement of radioactivity; sodium ion by means of measurements with a Beckman DU flame photometer or radioactivity measurements when NaZ4isotope was used as a tracer. When sodium ion concentration was determined by means of the flame photometer, the test solution was closely bracket,ed with two solutions of known sodium ion content. Equilibrium Resin.-The washed equilibrium resin was analyzed for each cation by means of complete exchange of both for a third ion which would not interfere in the determination. For example, nitric acid solutions were used to displace silver and sodium ions from the cquilibrium resin in the silver-sodium exchange experiments. The resulting solution was then analyzed as before. When radiochemical
Feb., 1953
EQUILIBRIUM Sl'UDIES O F THE
SILVER-SODLUM-HYU~~OGEN SYS'l'gM ON DOWEX 50
methods of analysis were used, however, i t was not necessary to remove the silver or sodium ion from the equilibrium resin. Material balances showed a check within 0.3% in every instance where radiochemical methods were used. Accuracy of the Analytical Methods.-The accuracy of the titrations of silver and hydrogen ion IS believed to be of the order of 0.1% and that of the other analytical determinations approximately 0.5%.
45
Discussion and Results
27
The experimental data for these exchanges are presented in Figs. 1-3. It was determined, by an experimental method described previously, that the maximum water uptake of the nominal 16%
255
36
d 18
9
0 Mole per cent silver resin Fig. 3.-Silver-sodium exchange.
0
20 40 60 80 Mole per cent. sodium resin Fig. 1.-Sodium-hydrogen exchange. MH+ %NaRa A' = __
MNA+
% &ea
100
.
25.0
20.0
15.0
4 10.0
5.0
0
40 60 80 Mole per cent. silver resin Fig. 2.-Silver-hydrogen exchange. 20
100
DVB resin in the hydrogen form was 103 g. per equivalent while that of the nominal 8% DVB resin in the same form was 200 g. per equivalent. It was also determined for t
