EXPT 5:
Qualitative Analysis
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Experiment 5 - Qualitative Analysis

Procedure:

Part D - Analysis of an Unknown Solution

  1. To about 20 drops of unknown solution add about 20 drops of dilute HCl in a small test tube. Record your observations.
  2. Centrifuge and separate the precipitate from the solution. Discard the solution.
  3. Add about 2 mL of distilled water and stir to wash the precipitate. Centrifuge and separate the precipitate from the solution and again discard the solution.
  4. Check for Pb2+: Add about 2 mL of distilled water to the test tube which contains the precipitate and place it in a beaker of boiling water for about 3 minutes. Mix occasionally. Record your observations. No change may be observed.
  5. Centrifuge and separate the precipitate from the solution. Transfer the solution to a clean test tube. Keep the precipitate for step 7.
  6. Add a few drops of K2CrO4 to the solution from step 5. A yellow precipitate confirms the presence of Pb2+ ions in the unknown solution. Record your observations.
  7. Check for Hg22+: Add about 10 drops of concentrated ammonium hydroxide, NH4OH, (located in the fume hood) to the precipitate from step 5. A black precipitate confirms the presence of Hg22+ ions in the unknown solution. Record your observations.
  8. Stir the substances in the test tube from step 7 and then centrifuge to separate the precipitate from the solution. Transfer the solution to a clean test tube.
  9. Check for Ag+: Add nitric acid, HNO3, drop=wise to the solution from step 8, until the solution becomes acidic. Place a small drop of the test tube solution on the blue litmus paper. If the blue litmus paper turns pink the test tube solution is acidic. If a white precipitate forms, Ag+ ions are in the unknown solution. Record your observations.

 

 



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