Qualitative Analysis of Anions

• In the previous two experiments, you have used qualitative analysis to determine the identity of various cations in a sample. In this experiment you will use qualitative analysis to identify the various anions in a sample.
• Specifically you will test for the presence of each of the following anions: CO2−3, SO2−4, PO3−4, SCN−, Cl−, NO−3.
• The methodology used in identifying the anions will be different from that which was used to identify cations. Here you will use a small portion of the unknown mixture (1 mL) to perform a spot test for each anion individually.
• In some cases the test for a particular ion will be complicated by the presence of other ions in the mixture that will interfere with the test. In these situations the interfering ions must be removed before the test can be performed.
• Chemicals


  • 1 M Na2CO3
  • 0.5 M Na2SO4
  • 1 M BaCl2
  • 0.5 M NaCl
  • 0.1 M AgNO3
  • 0.5 M NaNO3
  • 6 M HCl
  • 6 M HNO3
  • 6 M acetic acid
  • 6 M NaOH
  • Aluminum granules
• Equipment


  • 4 small test tubes
  • Dropper pipette
  • Test tube rack
  • Test tube holder
  • Pipette
  • Aspirator
• All waste generated by this lab is toxic and must be disposed of in the hazardous waste container!
• Unused samples of the unknown should be discarded in the hazardous waste container. Wash the empty test tube and return it to the instrumentation room.
• General Instructions


  1. Perform a positive control test on 1 mL of solution of the anion

  2. Perform a positive control experiment on 1 mL of a diluted solution of the anion

  3. Perform the same test on 1 mL of your unknown solution
• Test for the presence of carbonate ion, CO2−3


  1. Add 1 mL of 1M Na2CO3 (or your unknown) and 1 mL of 6M HCl to a small test tube

  2. Effervescence indicates the presence of CO2−3

  3. In the concentrated control solution you should see effervescence for at least a few seconds

  4. In the diluted control solution it may be necessary to place the test tube in a hot water bath in order to observe the effervescence

  5. For the unknown if no effervescence is observed, place the test tube in the hot water bath before concluding that CO2−3 is not present
• Test for the presence of sulfate ion, SO4−2

  1. Add 1mL of 0.5 M Na2SO4 (or your unknown) and 1mL of 6M HCl to a small test tube

  2. Next add a few drops of 1 M BaCl2

  3. A finely divided, white precipitate indicates the presence of the SO4−2 ion
• Test for the presence of chloride ion, Cl−


  1. Add 1 mL of 0.5 M NaCl (or your unknown) and 1 mL of 6 M HNO3 to a small test tube

  2. Next add 2 to 3 drops of 0.1 M AgNO3

  3. The formation of a white, curdy precipitate indicates the presence of Cl−
• Test for the presence of nitrate ion, NO3−


  1. Add 1 mL of 0.5 M NaNO3 (or your unknown) and 1 mL of 6 M NaOH to a small test tube

  2. Then add a few granules of aluminum metal and put the test tube in the hot water bath

  3. The reaction between Al and NaOH will produce H2 gas which will reduce the NO3− to NH3

  4. The NH3 can be detected by placing a piece of moistened red litmus paper directly above (but not in contact with) the mouth of the test tube

  5. If the red litmus paper turns uniformly blue (due to NH3 vapor coming out of the test tube) then it can be concluded that NO3− is present in the unknown

  6. Note that small blue spots produced on the red litmus paper are the result of spray from the basic solution in the test tube and do not necessarily indicate the presence of nitrate
• Lab Report: Qualitative Analysis of Anions using Spot Tests
• Group Number:________________________________________
• Lab Section:_______
• Table 1. Observations on the anion analysis.

  • Ion
  • Control
  • Diluted Control
  • Unknown

  CO2−3

  SO4−2

  Cl−

  NO3−
• Unknown ID number:____________________
• Ions present in your unknown:________________________________