Notes on Qualitative Analysis EDITOR'S NOTE:The following pepers have been collected over a period of months. A similar collection appeared in previoue August issues (J. CHEMEnnc., 35,401 (1958); 36,379 (1059); 37, 407 (1960); 38, 406 (1961); 39, 395 (1962)). It is the Editor's hope that collection into one place will prove more attractive to readers than the more frequently used editorial procedure of scatterO have ingitems such as these through the pages of several issues. We apologize to authors K ~ thus had to wait to see their work in print. We commend to readers' sttention the fact that often these represent the solution of problems given to freshman students in qualitative analysk courses. We hope that publication in these pages can stimulate just such activity. If readers merely incorporate these ideas into their own laboratory instructions, o w battle k only half won. If, beyond that, these ideas suggest to the readers that they uae their own ingenuity in similar fashion, we are gratified.
Alcidio Abr6o
Rad~ochern~stry D~v~sion lnst~tutode Energin Atorn~ca Sao Paulo, Brad
Separation and Identification of Copper in the Presence of Cadmium
I n the classical analytical procedures both copper and cadmium are precipitated together, and the separation and identification of cadmium is made in the presence of cyanide ion by precipitation with HzS. Only cadmium sulfide is precipitated because the stahility constant of the copper cyanide complex is greater than that of the corresponding cadmium complex. Due to the highly poisonous character of HCN, various methods have been described for the separation of both elements without HCN.' Vick and Harris" used anionic ion exchange resins to retain the complex anion formed between cadmium and bromium ions; cadmium was then eluted with ammonium hydroxide and precipitated with HIS. We suggest two modifications of their technique for sepamtion and identification of cadmium when copper is present. Separation of Copper with Cupferron
Cupferron, the ammonium salt of nitrosophenylhydroxilamine and a common analytical reagent, precipitates copper from acid solutions but not cadnuurn. The copper cupferrate is filtered off or extracted with chloroform. Precipitation. Into a beaker pipet copper solution (1 mg/ml) and cadmium solution (1 mg/ml), add sufficient sulfuric acid to make a 5% solution, and precipitate at room temperature with 10 ml of 1% freshly prepared cupferron solution. Filter using a medium porous paper, and wash the precipitate with a few milliliter of water, slightly acidified with sulfuric acid. Copper is identified by adding a few drops of 1:1 NHIOH to the precipitate to develop the characteristic blue color.
'See, for example, WHITYIHEAD, T. H., m n HATCHER, G. K., ~ m JOURNAL, s 39,399 (1962)and the references noted therein. 1 VICE,M. M., AND HARRIS, E. L., THIG J O U R N ~ ~38, , 414 (1961).
To the filtrate add sufficient NHIOH to make a slightly ammoniacal solution. Then add some thioacetamide crystals and warm. Observe the yellow cadmium sulfide precipitate. Extraction. Pipet into a separatory funnel cadmium and copper solutions, add enough HzSOl to make a 5% solution, and adjust the volume to 20-30 ml. Add 5 ml cupferron solution and extract with 5 ml chloroform. Allow the two phases to separate and discard the organic phase into another separatory funnel. Repeat the extraction three times. To the collected organic phases add a few milliliter 1 :1 NHIOH and shake. Let the phases separate. Observe copper and cadmium as above. Cation Exchange-EDTA
Sepamtion
An ion exchange column (0.8 cm id X 5 cm) is mounted with strong cation exchange resin (Nalcite HCR, 30-50 mesh). The resin is conditioned with 10 ml 1 M HC1 and washed with water until the effluent shows no acidity. To the solution containing the cadmium and copper ions (5 mg each) add 100 mg of ethylenediaminetetraacetic acid (EDTA) dissolved in a minimum of NHIOH, and adjust the pH of the solution to 1-3 with HNOa. Percolate the solution (about 15 ml) through the column a t about 2 ml/min and wash the column with 30 m15 g/l EDTA prepared in a minimum of N&OH and a t a pH of 1-3 measured a t the time of the experiment. The blue EDTA-Cu complex is not absorbed by the cation resin, but the cadmiumionsare. After washing the column with EDTA, elute the resin with 15 ml of 1.0 M HCl into a small heaker, warm the eluate on a hot plate, and add thioacetrtmide crystals. Then add 3 ml 1: 1 N&OH and cover the beaker with a watch -glass. Observe the yellow CdS precipitate. If necessary, copper may he directly identified in the blue effluent by adding a few drops of 5% aqueous ferrocyanide solution. Volume 40, Number 8, August 1963
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