DRAFT: This module has unpublished changes.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)
- Make sure all of the test tubes and materials are clean. Label four test tubes and pipets 1-4 to prevent contamination.
- 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.
- 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.
- Add 10 to 15 drops of the unknown solution to test tube 5.
- Repeat step 3 for test tube 5.
Procedure 1: Ba(NO3)2 Test
- Prepare a new set of test tubes as described in the setup above.
- 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-.
- Record observations.
- 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.
- Centifuge the mixture in the test tube and separate the supernatant from the precipitate and save them both. Record observations.
- 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.
- Add 6 M HNO3 drop by drop to the precipitate obtained (if it did) from the precipitate from your unknown.
- Observe if there is any dissolution. Then separate the precipitate from the supernatant. (No precipitate was formed).
Procedure 2: AgNO3 test
- Prepare a new set of test tubes as described in the set up.
- Dilute each solution with 1 mL of distilled water.
- Add 2 drops of AgNO3 to the four test tubes. Some of the anions should combine with the silver ion to form precipitates.
- Add NH3 by drops to the solution that contained the chloride ions until the precipitate dissolves. Record obseravations.
- Add two drops of AgNO3 to the supernatant 1 from Ba(NO3)2 test. Record observations.
- 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
- Add 10 drops of 0.2 M NaNO3 solution in a clean test tube.
- Add 3 M H2SO4 drop by drop until the solution is acidic after tested with litmus paper.
- Add 5 drops of saturated FeSO4.
- 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!
- Observe the presence of NO3. Record the observations.
- Add some unknown to a clean test tube and then reepeat steps 4-5. Record observations.
DRAFT: This module has unpublished changes.
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