GROUP I: THE ACID SULFIDE GROUP Purpose The following procedure will separate an
ID: 486154 • Letter: G
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GROUP I: THE ACID SULFIDE GROUP Purpose The following procedure will separate and identify the cations of Group II shown above. The tin may be in the form of a complex anion, Sncls These four ions did not (and will not) precipitate under conditions of Group I; that is, as chlorides. Ifwe lower the pH with the addition ofHCI and add sulfide in the form of thioacetamide (CH NH.CS), the four ions precipitate as sulfides. You may remove the flow sheet for the Group II cations as a reference while performing the lab procedure below. Laboratory Procedure Known: For your known mixture use 12 drops of Cd solution and 6 drops of the other cation solutions. 1. Make the solution just alkaline with 6MNHOH, then just acidic with 6M HCI and add 10 drops of thioacetamide. Heat the tube in a hot water bath for 4 minutes. Thioacetamide will hydrolyze in hot water to furnish small quantities of H2S. Cool the tube under the water tap and centrifuge. 2. Discard the liquid fraction and retain the precipitate consisting ofthe four cation sulfides. Add 20 drops of3M KOH and 1 drop of thioacetamide to the precipitate and heat in a hot water bath for not longer than two minutes. This will cause the tin to dissolve in the form of Sn(OH)sa. After heating, centrifuge and treat the precipitate according to #4 below. Treat the liquid fraction according to #3 below. 3. To the liquid fraction from #2 above, add 15 drops of6MHCI and 1 drop of thioacetamide. Heat in a hot-water bath for 2 minutes. Centrifuge. The presence of a yellow precipitate of SnS2 proves tin. 4. To the precipitate from #2 above, add 10 drops of 1M HCI. Heat 2 minutes in the hot- water bath. Centrifuge. Separate the liquid fraction from the precipitate. Treat the liquid according to #5 below, treat the precipitate according to #6 below. 5. To the liquid fraction from #4 above add 6M NHOH until it is basic to litmus paper. Add several drops ofthioacetamide and heat 1 minute in the water bath. A yellow precipitate ofcds confirms Cd 6. To the precipitate from #4 above add 10 drops of 6M HNO and heat in the water bath until the precipitate dissolves. Both the bismuth and the copper will dissolve in the nitricExplanation / Answer
Basically, the above procedure is used to analyze the sulfide salts of Barium, Copper, cadmium and Tin. Kindly follow the flowchart given in the question to analyze the unknown sulfide salt.
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