Mawin Wayne Hanson Centenary College Shreveport, Louisidno
Chloride, Bromide, and Iodide Determination
There is a need for a relatively simple identification for qualitative scheme of separnt,ion chloride, bromide, and iodide> particularly when three ions are present or when halide, sulfide, cyanide, and thiocyanate ions may interfere. Most analysis schemes ;ow in use invoke the precipitation of the along sulfide, and silver thiocyanate. The precipitate is treated in various wavs to wut the ions back into sohtion and then tests are made for the anions. ~h~ simple test described here is relatively free from interfering ions and may be used to identify halides in both inorganic and organic qualitative analyses. The test may be made, without interference, on a solution made uw from 1 ml each of 0.1 1M solutions of the following anions : (COa)-2, (Son)-', ( S O P , (P04)k3, (F)-I, (CZCI)-z, (Cr4)-2, (AsO&~, ( A s O P , (BO&', (CN)-', (CNS)-', (S)-', (C~HIC?)-~, (N03)-', (SH)kl, and (HCO.)kl -, Ferricyanide and ferrocyanide ions cause interference and must be removed by precipitating them with eadmium acetate. The centrifngate is used for testing. Procedure
Put four drops of the unknown solution (free of ferricyanide and femoeyanide) in a 4in. test tube. If the unknown is basic, add concentrated HNOa by drops with stirring until the unknown is just acid. Then add t x o drops of concentrated HNOJ, 0.5 ml CCI,, and shake the mixture vigorously. A pink-to-violet coloration of the CCI, layer indicates the presence of iodine. No coloration of the CCI, lsyer indicates the absence of iodine. If iodine is present, remove the CCL layer by means of a pipet, add one additional drop of concentrated HNOa and again extract with 0.5 ml CCI,. Continue the extractions until the CC14 layer is colorless or a very light pink.
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Journol of Chemical Educofion
To the aqueous layer add 2 rn! concentrated HNOa. Add 0.5 ml CCI, and shake vigorously. A reddish-to-strau-->-ellon coloration of the CCI, layer indicates bromine. No coloration of the CCI. indicates the absence of bromine. Remove the -~ .laver " CCI, layer by means of a pipet and extract the aqueous layer again with 0.5 ml CCI,. Continue the ertrartions until the CCI, layer is colorless. If there is some coloration of the aqueous layer after the bromine extraction, boil the solution until it becomes colorles~. Otherwise, boil the solution for approximately 30 seconds. If thiocvanate ion is absent, the hoilina is nnneeesasrv. TO- the rolorless aqueous mhtion; add 2-1 drops of a 5% aqueous silver nitrate solution. An immediate fonnation oi a white precipitate indicates chloride. No cloudiness or precipitate indicates the of chloride, ~
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The same procedure may be applied to a sodium fusion filtrate obtained from the fusion of metallic sodium and organic compounds. Cyanide, sulfide, sulfate, fluoride, and phosphate did not interfere with the analysis of a sodium fusion filtrate containing chloride, bromide, and iodide ions. If thiocyanate is absent and the iodide concentration is low, as indicated by a hght pink coloration of the CCL layer, it is not necessary to remove the CClr layer. The following proccdure may be used: To four drops of the unknown solution in a Gin. test tube add 2 drops of concentrated HNO, and 0.5 ml CCh. Shake well. A light pink CC1, lsyer indicates iodide. Add 2 ml of roncentrated HNOs to the mixture and shake well. A change in color from a light pink to a reddish-yellow or a straw yellow indicates the presence of bromine. X o chsnge in color indicates the absence of bromide. Remove the CCI, layer and extract again with 0.5 ml CC4. If the CCI, layer is practically colorless, add 2-3 drops of a 5% aqueous silver nitrate solution to the aqueous layer. An immediate formation of a white precipitate indir~tes the presence of chloride.
