Chem Lab 365 Procedure

Chem Lab 365 Procedure - Yontii Wheeler Chemistry 002...

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Yontii Wheeler Chemistry 002 Ashley Mills 3/24/11 Experiment 365: The Chemistry and Qualitative Analysis of Cations: Group II Precipitating, Separating, and Confirming Selected Group II Cations A. Precipitating Group II Sulfides 1. Get a container of a known mixture with the Group II cation from the lab instructor. 2. Using a clean dropper, put 15 drops of the known solution into a clean 10x 75 mm test tube. 3. Estimate the pH of the solution in the test tube using the short-range pH test paper. The solution should have a pH of 0.5+/- 0.3. This means there is a H 3 0+ ion concentration of approximately 0.35 M. If the pH is not within this range, then adjust it as follows. To adjust the pH: 1. Make 0.5 M solutions of HCl or NH 3 by diluting 1 drop of 6M solution with 11 drops of distilled water and mixing the solutions well with a glass-stirring rod. 2. Add the required amount of 0.5 M solution drop wise as you stir the solution until the pH is within the range. 4. With a clean dropper, add 10 drops of 1M-thioacetamide solution to the acidic solution made earlier. 5. Put the test tube in a water bath of boiling water. 6. While the reaction mixture in the test tube is heating, make a dilute solution of aqueous NH 3 by adding 3 drops of 6M NH 3 to 2mL of distilled water. Keep this solution for solution for later use however, if 0.5M NH 3 was already made you can use that instead of making a new batch. 7. Take the test tube out of the boiling water bath and cool it by running the outside of it under cool tap water. 8. Add 1 drop of the dilute NH 3 solution made earlier. 9. Stir the mixture very well with a clear glass-stirring rod. 10. Centrifuge the test tube for 2 min. 11. Do not separate the supernatant liquid from the precipitate and add 5 more drops of 1M thioacetamide to the mixture. 12. Put the tube back into the boiling water bath for 2 minutes. 13. Cool the test tube by running the outside under tap water. 14. Add 1 drop of the previously prepared dilute NH 3 solution using a clean dropper 15. Stir the mixture with a clean glass-stirring rod. 16. Centrifuge the test tube for 2 minutes. 17. Decant the supernatant liquid from the precipitate to remove it from the test tube.
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18. If Group II cations were the only ones present in the sample solution, discard the supernatant liquid. If the sample solution is going to be analyzed for Group III and/or Group IV cations, keep and label the supernatant liquid. 19. Add 1 mL of 0.1 M ammonium chloride (NH 4 CL) solution to the precipitate to wash it, 20. Stir the mixture thoroughly with clean glass stirring rod. 21. Centrifuge the test tube for 2 minutes. 22. Decant the supernatant liquid from the precipitate and then discard the supernatant liquid. Keep the precipitate to use in the next section. 23. Record all observations on Data Sheet 1.
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Chem Lab 365 Procedure - Yontii Wheeler Chemistry 002...

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