Use of lon-Exchange Resins without Columns Many texts' and papers2 describe the now commonplace use of ion exchange resins in some sort of column apparatus. Though a column setup is required for chromatographie-like separations, there often is little point in using columns for simple ion exchange. An excess of the appropriate resin ean he swirled in the test solution for several minutes, the resin filtered off and washed, the wash being added to the eluate. Such a procedure is quicker and less tedious than a column technique. The resins can he regenerated and washed in bulk, no columns need be packed and cared for, and especially important, the volume of the eluate and wash is minimized. Therefore, the author recommends that the concept of ion-exchange he somewhat divorced from that of column apparatus in texthooks and papers oriented towards introductory analytical chemistry. Intermediate courses should include discussion of the distribution coefficient. Whichever method is preferred, an interesting pair of salts for demonstrations is NaBF4 and NaBF30H. The tetrafluoborate ion is stable in aqueous solution hut the hydroxytrifluohorate is readily hydrblyzed. One equivalent of either salt in solution yields one equivalent of base after reaction with the hydroxide form of an anion exchange resin kg., DOWEXS-X). However, when one equivalent is reacted with the hydronium form of a cation exchange resin (e.g. DOWEXdO-X), the NaBF4 yields three equivalents of H F plus one of boric acid. The acid solutions yields one equivalent of HBFI hut the N ~ B F B O H sogeaerated can be titrated with standard base to a phenolphthalein endpoint for the HBF4 or HF, and similarly for the H:,BOa(as if it were monoprotonic) if mannitol is added. The basic solutions can he titrated with standard acid t o a methyl red endpoint.
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Vokel, A. L, "A Textbook of Quantitative Inorganic Analysis", 3rd ed. Longmans, Green and Co., London, 1971, p. 708. Morelli, B., and Lampugnani, L., J. CHEM. EDUC., 52,572 (1975). University of Victoria Victoria. R.C.. Canada
770 / Journal of ChemicalEducation
M.J. R. Clark
