DRAFT: This module has unpublished changes.

Equipment:

- Test tube (13), 10-mL

- Test tube rack

- Pipets (13), 1-mL, disposable

- Stirring rods (several)

- Litmus paper (15)

- 0.2 M Sodium sulfate (Na2SO4), 10 mL

- 0.2 M Monopotassium phosphate (KH2PO4), 5 mL

- 0.2 M Sodium nitrate (NaNO3), 5 mL

- 0.2 M Sodium chloride (NaCl), 5 mL

- Unknown anion solution, 20 mL

- 0.2 M Barium nitrate (Ba(NO3)2), 5 mL

- Saturated iron(II) sulfate (FeSO4), 2 mL

- 0.1 M Silver nitrate (AgNO3), 5 mL

- 6 M Nitric acid (HNO3), 5 mL

- 5 M Ammonia (NH3), 5 mL

- 3 M Sulfuric acid (H2SO4), 5 mL

- Concentrated H2SO4, 2 mL

- Distilled water

- Centrifuge

- Marking pen


Safety:

- Wear safety goggles at all time during this lab

- Avoid contacting concentrated acids with skin and eyes

- Wash acids off with water in case of skin contact

- Add concentrated acids to water very slowly


Method:

Procedure 1: Ba(NO3)2 test

1. Prepare a new set of test tubes as described in the Set Up

2. Add 2 or 3 drops of Ba(NO3)2 to the test tubes 1 through 4 to form precipitates between Ba2+ and some of the anions and record observations

3. UNKNOWN: Add Ba(NO3)2 by drops to the unknown solution until a precipitate forms. Stop adding Ba(NO3)2 after 2 drops.

4. UNKNOWN: Centrifuge the mixture and then using a clean test tube separate the supernatant (label Supernatant 1) from the precipitate (label Precipitate 1) and put them to the side

5. In test tubes 1 through 4, in the test tubes with precipitates, add 6 M HNO3 by drops until the solution is acidic when tested with litmus paper

6. UNKNOWN: Add 6 M HNO3 by drops to the precipitate, if any, obtained from the unknown (Precipitate 1) and observe is there is any dissolution

7. UNKNOWN: Obtain another clean test tube and separate the supernatant from the precipitate, if any, and label them as Supernatant 2 and Precipitate 2 and record observations


Procedure 2: AgNO3 test

1. Prepare a clean set of test tubes and label them 1 through 4 and described in the Set Up

2. Use a graduated cylinder to dilute each solution with 1 mL of distilled water

3. Add 2 drops of AgNO3 to each of the test tubes. Some anions should combine with the silver ion to form insoluble precipitates

4. Add Nh3 solution drop by drop to the solution that contained Cl- ions until the precipitate dissolves

5. UNKNOWN: Add 2 drops of AgNO3 solution to Supernatant 1 and record observations

6. UNKNOWN: Add 2 drops of AgNO3 solution to Supernatant 2 and then add NH3 solution until the precipitate dissolves and record observations

 

Procedure 3: The brown ring test for nitrate ion

1. Obtain a clean test tube and add 10 drops of 0.2 M NaNO3 solution

2. Add 3 M H2SO4 by drops while stirring until the solution is acidic when tested with litmus paper

3. Add 5 drops of freshly prepared iron(II) sulfate (FeSO4) solution

4. Tilt the test tube and carefully add 5 drops of concentrated HcSO4 so the drops flow down the side of the test tube and float on top of the solution

5. Observe the indication of the presence of NO3- and record observations

6.  UNKNOWN: Obtain a clean test tube and add a few drops of fresh unknown and perform the test for nitrate ions and record your observations

DRAFT: This module has unpublished changes.