Separation and Qualitative Determination of Cations and Anions

Separation 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 qualitative analysis to determine which cations and anions were present in a solution. II. Procedure: Qualitative Analysis of Cations 1. Separation of the Silver from Iron, Copper, and Zinc ions. First add 8 drops of 6 M HCl to the solution and stir. A white Ag precipitate should form and indicate that Ag is present. Then centrifuge the solution. To double check that the precipitation is complete, add one more drop of the 6 M HCl. Next, centrifuge, pour off, and save the clear liquid because it will be used again in step three. Label it 1c. Last, wash the precipitate with 1 mL of distilled water, centrifuge and discard the wash water, however the precipitate should be saved. Label the precipitate 1d. 2. Confirmation of Silver First, add 1 mL of 6 M NH 3 to the precipitate formed in part 1d of the procedure, and stir until the precipitate completely dissolves. Now, add 15 drops of 6 M HCl to the solution. If silver is present, heat will be given off and the test tube could get very warm. Next, stir the solution and test it with pH indicator paper. The solution should be acidic. If it’s not, add more HCl, and if the white precipitate forms in the solution, this means that silver is present. Dispose of the silver compound. 3. Separation of Iron and Copper from Zinc Add 6 M NaOH to the solution labeled 1c. Be sure to stir while the NaOH is being added. Continue to add this until the solution becomes basic. Once it’s basic, add three more drops. Next, stir the solution and place it in a hot water bath for three minutes. If a precipitate forms, that means that copper, iron or both elements may be present. Centrifuge the solution, and separate the solid from the liquid. Save the clear solution and label it 3c. Wash the precipitate with a mixture that contains 10 drops of 6 M NaOH and 10 drops of water. Centrifuge this and be sure to discard the wash water. Save the precipitate and label it 3e. 4. Separation of Iron from Copper; Confirmation of Copper Add five drops of water to precipitate 3e and add 6 M H 2 SO 4 dropwise until the solution is acidic, and stir until the precipitate is dissolved. To the new solution add 6 M aqueous NH 3 until the solution is basic. Then add 1 mL extra. Centrifuge and separate the supernatant liquid from the precipitate and save the precipitate, label it 4d. Dispose of the copper solution.
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5. Confirmation of Iron Wash the precipitate labeled 4d, and add 6 M H 2 SO 4 until the precipitate dissolves. Add 5 drops of 0.1 M KSCN to the new solution. Dispose of the solution. 6. Confirmation of Zinc To the solution labeled 3c, add drops of 6 M HCl to make it slightly acidic. Then add three drops of 0.1 M K
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This note was uploaded on 05/25/2010 for the course CHEM 101 taught by Professor Fricke during the Spring '10 term at Canisius College.

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Separation and Qualitative Determination of Cations and Anions

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