Seperation and Qualitative Determination of Cations and Anions

Seperation and Qualitative Determination of Cations and Anions

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Separation and Qualitative Determination of Cations and Anions I. Purpose: The purpose of this lab was to use analysis to identify both cations and anions in solutions, which were later, used to determine the ions present in an unknown solution. II. Procedure: 1. Separation of the Silver from Iron, Copper, and Zinc Ions. a. Add 8 drops of 6 M HCl to the solution to be analyzed. Stir. A white precipitate indicates that the Ag+ ion is present. b. Centrifuge the solution and test to be sure that precipitation is complete by adding one more drop of 6 M HCl. No additional precipitate should form. If more precipitate does form, continue adding 6 M HCl until precipitation is complete. c. Centrifuge, pour off and save the clear liquid into a second test tube for procedure 3. Alternatively, use a Beral-type pipet to draw off the supernatant liquid to transfer it to another test tube. d. Wash the precipitate by adding 1 mL distilled water and stirring. Centrifuge and discard the wash water. Save the precipitate for procedure #2. 2. Confirmation of Silver. a. To the precipitate from procedure 1 d , which is AgCl, add 1 mL 6 M NH3. b. Stir until the precipitate completely dissolves. c. Add 15 drops of 6 M HCl to the solution. The solution will smoke and the reaction between the strong acid and the base will give off heat whether or not silver is present. The test tube may get very warm. d. Stir and test with pH indicator paper or litmus paper to be sure the solution is acidic. If it is not acidic, add more HCl. The reappearance of the white AgCl precipitate in the acidic solution confirms the presence of silver. e. Dispose of the silver compound as directed by the instructor. 3. Separation of Iron and Copper from Zinc. a. To the solution saved from procedure 1 c , add, with stirring, 6 M sodium hydroxide, NaOH, until the solution is basic and then add 3 more drops. b. Stir and place the test tube in a hot water bath for 3 minutes. The formation of a precipitate indicates the presence of either copper or iron or both. c. Centrifuge the solution, and separate the clear solution from the solid. Save the clear solution, which may contain Zn(OH)42– ions for procedure #6. Centrifuge
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d. Wash the precipitate with a mixture of 10 drops of 6 M NaOH and 10 drops of water. e. Centrifuge and discard the wash water. Save the precipitate for procedure #4. 4. Separation of Iron from Copper; Confirmation of Copper. a. To the precipitate from procedure 3, add 5 drops of deionized water. b. Add 6 M H2SO4 dropwise until the solution is acidic when tested with litmus paper (about 6drops). Stir to dissolve precipitate. c. To the solution, add 6 M aqueous NH3 until the solution is basic to litmus, and then add1 mL extra. d.
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Seperation and Qualitative Determination of Cations and Anions

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