EXPERIMENTS WITH ION-EXCHANGE RESINS' ROBERT H. SCHULER, ALFRED C. BOYD, JR., and DANIEL J. KAY Canisius College, Buffalo, New York
WITHIN the
past several years, there has been considerable development in the production of new synthetic ion-exchange resins. This development has been accompanied by numerous applications of these resins to various problems in research. The commercial importance of the resins makes it highly desirable that the student in the chemistry and in the chemical engineering curriculum obtain some familiarity with their fundamental properties and principles of operation and with the techniques involved in their use. While ion-exchange methods themselves are not new, the current interest in this tool is emphasized by the recent appearance of numerous articles on this subject in the various journals. The solution of such problems as the isolation and purification of certain rare earth (1, 8, 3) and transuranic (4, 6) elements has been accomplished (6). Spedding has described the pilot plant scale separation of the rare earths (7). Ion-exchange resins have aided in the isolation of antibiotics (8). In the field of analytical chemistry, the use of resin techniques can be applied to the elimination of interfering substances (9). A general, popular review of the uses of ion-exchange resins is given by Walton (10). Several otherarticleshaverecently appeared in t h e J o u ~ NAL OF CHEMICAL EDUCATION on this subject (11, 18). Student experiments involving techniques employing ion-exchange resins are now quite feasible as a result of the availability of high-grade, high-capacity resins in laboratory quantities. These experiments may be appropriately introduced into the semiadvanced inorganic or physical chemistry program. Ion-exchange methods orovide the field of inoreanic chemistrv with a
separation process quite comparable in significance to that of distillation in organic chemistry. It is the purpose of this paper to describe suitable experiments which are performed by the senior chemistry students in our laboratories. Previously, Daniels, et al., in their "Experimental Physical Chemistry" (IS), have suggested the use of ion-exchange resins in adsorption equilibrium experiments similar to the familiar study of the adsorption of acetic acid on charcoal. However, as the latter system has already been investigated by our junior students, little would be gained by having them perform an almost identical experiment. An experiment involving the column separation (similar to a chromatographic separation) of two ions suggests itself as suitable for ionexchange studies by the students. An experiment of this type is completely different from those normally performed in the undergraduate courses. We have found that it does stimulate the interest of the student. In order to choose an appropriate system for the study, one must first consider which analytical tool i t is most desirable to employ in following the elution curves. We have chosen, for this purpose, volumetric titration in order that the student can conveniently and quickly analyze the large number of samples obtained during the course of the experiment. This also serves, partially a t least, to correct the situation in the physical chemistry laboratory where chemical analytical methods are almost completely de-emphasized in favor of physical tools. Other institutions may wish to use other methods, e. g., colorimetric or radiochemical methods, for the analyses.
'Presented at the 118th Meeting of the American Chemical Society, Chicego, Illinois, September 3-8, 1950.
COPPER-SILVER SEPARATION
... . .. ... ..., ~ i g - I.
E I - ~ I O ~of
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The ions of copper and silver have been found to provide a suitable system for these studies. The silver ion is readily titrated with potassium thiocyanate using ferric alum as the indicator while an iodometric titration of copper with sodium thiosulfate can easily be carried out. Figures 1 and 2 represent, respectively, the data obtained for the elution of copper and silver ion alone from a 50-cm. column of Amberlite I R 100-H resin. This is the hydrogen form of the resin. The column is conveniently made by packing an ordinary stopcock buret with the resin. The stopcock, then, provides a means of regulating the flow of material through the column. The ion (as silver or cupric nitrate in 0.1 N solution) is adsorbed a t the to^ of the column and washed with distilled water. ~he'effluentshould test negatively for
APRIL, 1951
both ions. The copper and silver ions are then eluted by passing 1 M sodium nitrate solution through at the rather rapid rate of 3 to 4 ml. per minute. The concentration of silver ion in the effluent is determined by titrating the subsequent 10-ml. samples with 0.05 N potassium thiocyanate. In the case of copper, potassium iodide is added to the sample, and the liberated iodine is titrated with 0.05 N sodium thiosulfate. The iodine serves as its own indicator in this titration. Toward the end of the elution, it will be found necessary to take samples larger than 10 ml. in order to obtain enough ion for the analysis. Because the analysis yields the amount of ion contained in a definite sample, the data are plotted in the form of a histogram rather than as a smooth curve. If the sample size differs from 10 ml., then the titration must be calculated in terms of the amount of ion contained in 10 ml. (or some other suitable volume). This value is then spread over the entire volume taken. The relatively great scatter of the experimental points results from the fact that only a few milliliters of titrant are required for each sample. This is necessary since the amount of ion is limited by the capacity of the resin. It also serves to speed the analysis considerably -a necessary requirement since the available time is severely limited. It is believed that this sacrifice of precision is not seriously detrimental to the experiment, since it is only desired to show the general nature of the elution curves. Figure 3 represents the separation of the binary copper-silver system. The curves are obtained as before with the exception that the effluentsample is split in half before the titrations are carried out. The ferric alum indicator used in the silver titration interferes in the copper titration, making it necessary to use a separate sample for each component. It is seen that in this separation the copper is eluted before the silver. In general, the curves for the copper ion are much steeper and less drawn out than in the case of silver. In the curve of Figure 3, 65 per cent of the copper ion is eluted without any trace of silver. This effect, of course, increases with longer columns and decreases with shorter columns. The elution of copper before silver appears to be anomalous since the lower valence states are normally expected to be held to the
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resin less strongly than the higher valence states. However some difficulties are undoubtedly involved in this case due to the complexing of the ions. In performing ion-exchange experiments, one must be careful not to attempt to separate too great a quantity of material. If the resins become saturated with the ions the separation processes will not work. The maximum exchange capacity of the resin employed here is approximately 1 milliequivalent per ml. As mentioned before, this severely limits the analytical techniques which it is possible to employ. The following approximate values for the various variables are suggested for the experiments. None of the quantities is critical, so some variation is possible. Amount of ion.. . . . . . . . . . . . . . . . . . 3 milliequivalenta Column length.. . . . . . . . . . . . . . . . . .50 om. Column cross section.. ............1em.' Elutrient.. ..................... . 1 M sodium nitrate Rste of elution.. ................ . 3 to 4 ml./min. Sample size.. . . . . . . . . . . . . . . . . . . . .10 ml. Titrant concentration.. .......... .0.05 N
In the experiments described here, the student is required to perform numerous titrations (50 or more). He therefore becomes accustomed to performing titrations in a routine manner, something which is normally not considered in the analytical laboratory. The appearance of a large amount of data during the course of the afternoon also serves to create interest in the experiment. The determination of one binary separation curve is sufficient to keep a pair of hard-working students quite busy for a full afternoon laboratory session. If less time is available, it may be desirable to have the students study the elution of a single ion. The elution curves for different ions obtained by different students under similar conditions can then be compared as indicated by the comparison of Figures 1 and 2.
Important from the instmctional point of view is the fact that the experiments themselves are almost entirely foolproof and require, therefore, little supervision. It should be mentioned that the Amberlite resins are available in pound quantities a t reasonable cost. Although the resins may be regenerated, we prefer to have each student start with fresh resin.
JOURNAL OF CHEMICAL EDUCATION ACKNOWLEDGMENT
We wish t o thank Dr. Paul Klaas of the Rohm and Haas Co. for supplying certain resins for our studies.
(6) D ~ ~ E L Is?.,, "Outlines of Physical Chemistry," John Wiley and Sons, New York, 1948, p. 553. (7) SPEDDING, F. H., el al., J. Am. Chem. Soc., 69,2812 (1947).
(8) DOERY,H.M., AND E. C. MASON,Anal. Chem., 22, 1038 11950> - - - -,. LITERATURE CITED (9) K ~ M N R., , ibid.,21, 87 (1949). (1) KETELLE,B. H., AND G. E. BOYD,J. Am. C h m . Soe., (10) WALTON, H.F., Sn'. Am., 183, No. 5, 48 (1950); see also 69,28M) (1947). E. R. TOMPKINS, J. CHEM.EDUC.,26,32, 92 (1949). (2) SPEDDING, F.H., A. F. VOIGHT,E. M. GLADROW, AND N. R. J.F..mo J. Crows, J . CAEM.EDUC..27.673 (11) CASTKA. . (1950). . SLEIGHT,ibid., 69, 2777 (1947). (12) PETERSON,s.', J. CAEM. ED&, 28, 22 (195i). (3) HAENS,D. H., AND E. R. TOMPPJNR, ibid., 69,2792 (1947). (13) DANIELS.F.. .I H. . MATEEWS.J. W. WILLIAMS. P. BENDER. (4) STREET,K., JR., AND G. T. SEABORG, ibid., 72, 2790 (1950). G. w.' M'URPHY,AND R.'A. ALBERTY," ~ x ~ e r i m e n t a i (5) THOMPSON, S. G., B. B. CUNNINGHAM, AND G. T. SEARORG, Physical Chemistry." McGraw-Hill Book Co., Inc., New ibid., 72, 2799 (1950). York, 1949, p. 247. \
