Ronald Rich' Bethel College North Newton, Konsas
Dissolving Difficultly Soluble Salts with Chelating Ion Exchange Resins
Chelating resins such as Dowex A-l and Chelex 100 can be represented by the formula RN(CH2C02Na)2in the sodium form. Reactions of the type 2RN(CF1.CO2-),
+ BaSO,
-
Ba(RN(CH,CO&)z-'
+ SO4'-
provide a new way of separating the ions of some difficultly soluble salts. I n qualitative analysis the unknown is first ground fine and then mixed with the wet resin (50-100 mesh). The mixture is allowed to stand, possibly with heating, until only the resin beads are visible. The resin is rinsed with water which is then tested for anions. The cations are eluted with 6 M HNOs. The table shows approximate dissolving times, a t room temperature, for a number of compounds. The very stable complex, HgIaz-, is also decomposed by the resin. Complete removal of I-, however, requires rinsing the resin with about 50 times its volume of water. Possibly mercury is first held as RN(CH2CO&HgI-. The elution of Hg2+, Ag+, and Cr3+ from the resin is more difficult than that of other
' Address 1863-4. chusetts.
414
/
Harvard University, Cambridge, Massa-
Journal of Chemicol Education
cations. The first two are reduced to the metals in the presence of residual KaOH which can be mashed out in the regenerated resin. Rapid and essentially quantitative elution of the three ious requires. respectively, at least 6 ill HNOI, conc. HSOa, and either aqua regia or Na209,with destruction of resin in the last cases. The presence and removal of chromium ions are easily revealed by color. Acknowledgnzent. This work was part of a study aided by the Research Corporation. The exprrimental work was done by Duane D. Schroeder. Dissolvina Timer a t Room Tem~erature
Com~ound PbSOl PbI, PbCrO, PbdPOh BBSO, B4POdr CaFs AgCl AgI HgIx M~~CO(CN)O)S Z~~CO(CN)~~
Diasolvina- time 5-10 min 5-10 min 30 min 30 min 1-6
hr
15 min 1 hr 3 0 4 5 min 1 hr 30-45 min 10-15 min 15 min
.
