DRAFT: This module has unpublished changes.

Materials and Equipment

  • 13 10 mL Test tubes
  • Test tube rack
  • 13 disposable pipets
  • Stirring rods
  • Litmus paper
  • 10 mL of 0.2 M Sodium sulfate
  • 5 mL of 0.2 M Monopotassium phosphate
  • 5 mL of 0.2 M Sodium nitrate
  • 5 mL of 0.2 Sodium chloride
  • 20 mL of unknown anion solution
  • 5 mL of 0.2 M Barium nitrate
  • 2 mL of Saturated iron (II) sulfate
  • 5 mL of 0.1 M Silver nitrate
  • 5 mL of 6 M Nitric acid
  • 5 mL of 5 M Ammonia
  • 5 mL of 3 M Sulfuric acid
  • 2 mL of concentrated H2SO4
  • Distilled water
  • Centrifuge
  • Marking pen

Procedure (Setup)

  1.  Make sure all of the test tubes and materials are clean. Label four test tubes and pipets 1-4 to prevent contamination.
  2.  Add 4 to 5 drops of KH2PO4, Na2SO4, NaCl, and NaNO3 to the test tubes. Test tube 1 contains a phosphate anion, test tube 2 contains a sulfate anion, test tube 3 contains a chloride anion, and test tube 4  contains a nitrate anion.
  3.  Add 5 M ammonia to each solution until it becomes basic. Test it with the litmus paper after it is mixed well by touching the solution in the test tube with a clean stirring rod and then touch a piece of litmus paper to the stirring rod.
  4.  Add 10 to 15 drops of the unknown solution to test tube 5.
  5.  Repeat step 3 for test tube 5.

Procedure 1: Ba(NO3)2 Test

  1.   Prepare a new set of test tubes as described in the setup above.
  2.  Add 2 to 3 drops of Ba(NO3)2 to test tubes 1 through 4 and determine which anions form into precipitates. The ones that turn into precipitates are (SO4)2- and (PO4)3-.
  3.  Record observations.
  4.  Add Ba(NO3)2 to the unknown solution drop by drop until a precipitate occurs. This should happen after adding 1-2 drops. If it doesn't, stop adding the Ba(NO3)2.
  5.  Centifuge the mixture in the test tube and separate the supernatant from the precipitate and save them both. Record observations.
  6.  To the test tubes that contained a precipitate when Ba(NO3)2 was added, add 6 M HNO3 drop by drop until the solution is acidic when tested with litmus paper. (PO4)3- dissolved in HNO3.
  7. Add 6 M HNO3 drop by drop to the precipitate obtained (if it did) from the precipitate from your unknown.
  8.  Observe if there is any dissolution. Then separate the precipitate from the supernatant. (No precipitate was formed).

Procedure 2: AgNO3 test

  1.  Prepare a new set of test tubes as described in the set up.
  2.  Dilute each solution with 1 mL of distilled water.
  3.  Add 2 drops of AgNO3 to the four test tubes. Some of the anions should combine with the silver ion to form precipitates.
  4.  Add NH3 by drops to the solution that contained the chloride ions until the precipitate dissolves. Record obseravations.
  5.  Add two drops of AgNO3 to the supernatant 1 from Ba(NO3)2 test. Record observations.
  6. Add two drops of AgNO3 to supernatant 2 from the Ba(NO3)2 test. Add NH3 until the precipitates dissolve.

Procedure 3: The brown ring test for nitrate ion

  1. Add 10 drops of 0.2 M NaNO3 solution in a clean test tube.
  2.  Add 3 M H2SO4 drop by drop until the solution is acidic after tested with litmus paper.
  3.  Add 5 drops of saturated FeSO4.
  4.  Tilt the test tube to a 45 degree angle and add 5 drops of concentrated H2SO4 carefully so the drops flow down the slide of the test tube and then float on the top. Do not mix the solution!
  5.  Observe the presence of NO3. Record the observations.
  6. Add some unknown to a clean test tube and then reepeat steps 4-5. Record observations.

 

DRAFT: This module has unpublished changes.