To test for Ag+
1. add 2 drops 6M HCl to 1 mL of unknown sample. Centrifuge (3-4 minutes). Add 1 more drop of 6M HCl and centrifuge (if necessary). A precipitate will form; decant (pour off) solution to another test tube (save solution)
2. wash precipitate from step 1 with 1 or 2 mL of distilled water. Stir, centrifuge, and decant the liquid (can be discarded). Then add 1 mL of distilled water to precipitate and place the test tube in boiling water. Let the test tube boil, and stir occasionally. Centrifuge the hot test tube (solution) and then decant after centrifuging (save the decant solution). Save the precipitate.
3. Add 10 drops of 6M HNO3 to the precipitation from step 2 and stir it. Centrifuge and decant the solution (save it).
4. Add 6M HNO3 to the solution from step 3 until it is acidic toward litmus paper. If Ag+ is present in the acidic solution, a white precipitate of AgCl will form.
To test for Cu2+ and Sb3+
1. Add 15M NH3 to 1 mL of unknown sample until the solution is basic to litmus paper. A precipitate may form at this point due to the formation of insoluble oxychlorides of bismuth, tin, or antimony. Add 1 drop 6M HCL for each mL of solution. Verify the pH level by using methyl violet paper, the paper should turn blue-green. Adjustment may be necessary to achieve the blue-green color. Add HCl or NH3 until it is almost the same blue-green color.
2. Add 15-20 drops of 1M thioacetamide to solution and heat in boiling water for 5 minutes. Centrifuge and decant to another test tube (may contain Fe and Cr). Test solution for completeness of precipitation by adding 2 drops of thioacetamide and letting it sit for 1 minute. If precipitation forms, add a few more drops of thioacetamide solution and heat again. Combine the two batches of precipitate. Wash precipitate with 1 M NH4Cl solution, stir, and warm in bath water; centrifuge, and discard the wash solution.
3. To sulfide precipitate from step 2 add 15 drops of 6M KOH, 2mL of water, and 3 drops 1M thioacetamide. Heat solution in boiling water for 5 minutes and stir occasionally. Centrifuge and decant the solution. Wash any precipitate remaining twice with 5 drops of water and combine the washings with the solution. Tin and antimony will be present in the solution as complex ions, and copper and bismuth will remain as undissolved sulfide precipitate. Save precipitate for later.
4. Add 12 M HCL to the solution from step 3 until it is acidic toward litmus paper. When acidified, some tin and antimony will precipitate as orange sulfides. Add 5 drops of 1M thioacetamide and heat. Centrifuge and decant solution (this solution can be discarded)
5. Add 10-15 drops of 12M HCl to the precipitate from step 4 and heat for 5 minutes to dissolve precipitate. Continue heating until H2S is gone. Centrifuge out any insoluble sulfur residue.
6. Add 0.5 grams of oxalate acid and 2 mL of water to remainder of solution from step 5. Heat the solution, if necessary, to dissolve the oxalate acid. This reagent forms a stable complex ion with Sn4+. Add 10 drops of 1M thioacetamide and heat. Formation of an orange precipitate indicates the presence of antimony.
6. Add 30 drops of 6M HNO3 to remaining sulfide precipitate from step 3. Heat solution gently in boiling water to complete dissolution of the sulfides. Centrifuge the solution to remove sulfur and decant it into a small beaker. Place beaker on hot plate and evaporate the liquid to a volume of about one-half mL. DO NOT LET SAMPLE DRY OUT.
7. Add 15M NH3 dropwise to the solution obtained in step 8 until it is basic toward litmus paper. Add a few more drops. The formation of a deep blue solution indicates the presence of copper.
Testing for Fe3+ and Cr3+
1. [If a solution is being used from which group II cations have been precipitated, remove the H2S and excess acid by boiling the solution in a small beaker until a volume of about 1 mL. Remove any sulfur residue by centrifuging the solution.] [if a solution being used contains only group II ion, then use 1 mL of this solution.]
2. Add 3 drops of 3% H2O2 to 1 mL solution from step 1. Add 15 drops of 6M NaOH to solution to make it strongly alkaline (basic). Stir for 1 minute and boil to remove all excess H2O2. After H2O2 is decomposed, solution will âbumbâ. If oxidation of chromium (II) has occurred, the solution will be yellow. If not, add 3 more drops of H2O2 and boil again. Centrifuge and decant. Save precipitate (contains Fe3+) and solution (contains Cr3+).
3. Acidify solution from step 2 by adding drops of 15 M HNO3(about 5 drops) and test with litmus paper. Add 6M NH3 drop by drop with mixing until solution is basic. This treatment will precipitate Al3+, will be gelatinous white. May appear yellow because of the presence of CrO42-. Centrifuge and decant the solution, it contains CrO42-. Add 1 M BaCl2 to solution from step 3 to precipitate yellow BaCrO4. If precipitate is slow to form, heat in boiling water. Centrifuge the solution and decant. Dissolve the precipitate in 3 drops of 6M HNO3; heat and stir. Add 4 drops of water and cool it down. Add 6 drops of diethyl ether followed by 1 drop of 3% H2O2. Shake gently, and allow layers to settle. A blue color in ether (top) later confirm test for chromium.
4. Add 8 drops of 15M HNO3 to precipitate from step 2. Heat until precipitate is dissolved. Allow to cool and add 10 drops of 1M NH4Cl and then add 15 M NH3 until solution is alkaline to litmus paper. This will precipitate iron as brown. Then add 4-5 drops of NH3 solution and stir. Centrifuge and decant solution (this solution may be discarded).
5. Dissolve the precipitate from step 5 by adding 10 drops of 6M HCl. Dilute with 2mL of distilled water and add 2 drops of 0.5M KSCN. A blood-red color indicates presence of Fe3+.
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I will be given 3 mL of an unknown sample and I will have 75 minutes to do a qualitative analysis for Ag, Cu, Sb, Fe, Cr.
I need help coming up with a flow chart based on the above steps so that it is makes this class assignment smoother since I will only be given 75 minutes to complete it.
Thank you!
