Hypothesis-Color change will indicate CationTo analyze an unknown mixture for the presence of Ag+, Hg22+, and Pb2+
G2-1. Oxidation of Sn2+ and Precipitation of Group 2
Place 7 drops of "known" or "unknown" solution in a dish. Add 4 drops of 3% H2O2 and 4 drops of 2M HCl. Then boil the solution over the flame of your burner. If the ormation of brown areas on the bottom of the dish it means that it is overheating. If brown areas is present, move the solution around until the brown area disappears.3 drops of solution should be present after the dish cooling. Add 10 drops of 6M HCl. evaporate the contents of the dish to a sticky mass, be careful again so it won’t overheat. Let the dish cool, and then add 5 drops of 2M HCl and 5 drops of distilled water. Stir the contents to dissolve residue and then put it to a small test tube. Afterwards you then add 10 drops of 1M thioacetamide to the solution in the test tube. Stir the solution and heat the test tube in a boiling-water bath for about 10 min or more. Keep stirring the solution while it is being heated. After the 10 min, add 10 drops of hot water and 10 drops of 1M thioacetamide and 2 drops of 1M NH4C2H3O2 (ammonium acetate). Mix and heat in the boiling-water bath for 10 more minutes, stirring occasionally. Cool, centrifuge, and using a pipet, decant into a test tube. Test the decantate for completeness of precipitation by adding 3 drops of H2O, 1 drop of 1M NH4C2H3O2, and 2 drops of 1M thioacetamide. Afterwards you then mix and heat in the hot water bath for 1 min. Continue heating for 3 mins until color precipitate forms. A hint of cloudiness may develop due to the formation of colloidal sulfur. Repeat the precipitation procedure until precipitation is complete. If the decantate is to be observed for groups 3 and 4, put it to a dish and boil it to reduce the volume to about 0.5 mL. If not, remove it. Put the solution to a test tube that is labeled and save it for procedure G3-1. After you are done rinse the dish with 6 drops of water and add the washing to the test tube and stopper it. Wash the precipitate three times with 10 drops of hot water and then wash it twice with 20-drops of then solution and 1M NH4C2H3O2. Stir the washing liquid and precipitate with a stirring rod before each centrifugation. If the precipitate forms colloidal suspension, add 10 drops of 1M NH4C2H3O2 and heat it in the boiling water. Remove the washings.
G2-2. Separation of Sn4+ from PbS, CuS and Bi2S3
To the precipiatate for Procedure G2-1 add 10 drops of (ammonium sulfide) solution and stir well. Then heat for 3 to 4 mins in the boiling hot water. Remove the test tube from the water bath as necessary to avoid excessive frothing. Centrifuge, decant, and save the decantate. Repeat the process using 7 drops of (NH4)2S. Centrifuge it. Combine the decantate with the first. Stopper the combined decantate and save for analysis for tin (Procedure G2-5). Wash the precipitate twice with 20-drop portions of a hot solution prepared by mixing equal volumes of water and 1M NH4C2H3O2.
G2-3. Separation and Identification of Pb2+
Put 1 mL (20 drops) of 3M HNO3 to the test tube containing the precipitate from Procedure G2-2. Mix thoroughly and transfer the contents to a dish. Boil the mixture for 1 min. Add more HNO3. Put the decantate to a dish and add 6 drops of 18M H2SO4.Evaporate the solution until the volume is