Group IV and V Cation Analysis

• Analysis of Known Mixture of Group IV and V Cations

  1. Take 15 drops of the fresh test solution

  2. Add 15 drops of 3M (NH4)2CO3

  3. Stir to thoroughly mix

  4. Centrifuge for 2 min

  5. Decant and keep the supernatant for group V tests

  6. Keep the precipitate for group IV cations analysis
• Wash the precipitate of step 1

  1. Re-suspend it in 15 drops of distilled water under stirring

  2. Centrifuge for 2 min

  3. Decant and keep the precipitate

  4. Discard the supernatant

  5. Add 5 drops of 6M acetic acid to the precipitate

  6. Heat for half-min while stirring to dissolve the precipitate

  7. Add 2 more drops of 6M acetic acid while heating and stirring if needed

  8. After the precipitate has dissolved, add 3 more drops of 6M acetic acid to make a CH3COOH / CH3COO− buffer
• Add 10 drops of 0.1M K2CrO4

  1. Stir to mix

  2. Heat for 1 min

  3. Immediately centrifuge for 2 min

  4. Decant while hot

  5. Keep the supernatant for analysis of Ca2+

  6. If a light-yellow precipitate is formed, it is most likely BaCrO4 due to Ba2+ present in the test sample

  7. Keep the precipitate for the flame test
• Wash the precipitate of step 2

  1. Re-suspend it in 15 drops of distilled water

  2. Centrifuge for 2 min

  3. Decant

  4. Discard the supernatant water

  5. Add 5 drops of 12M HCl to the precipitate

  6. Stir to mix

  7. Heat in a boiling water bath for 2 min to dissolve the precipitate

  8. Perform the flame test
• To the supernatant from step 3

  1. Add 10 drops of 0.2M ammonium oxalate ( (NH4)2C2O4 )

  2. Stir to mix

  3. Centrifuge for 2 min

  4. Decant

  5. Discard the supernatant

  6. Observe the precipitate
• Dissolve the precipitate of step 5


  1. In 3 drops of 6M HCl

  2. Perform the flame test
• Group V cations


  1. Evaporate excess water from the supernatant of step 1 by heating

  2. If any solid residue is left it is due to group V cations

  3. Add a drop or two drops of water to dissolve the precipitate

  4. Perform the flame test
• Used heavy metal ion solutions or precipitates are disposed of in a labeled metal waste disposal container, do not drain these solutions down the drain or in the regular trash
• If the solution imparts yellow-green color to the flame, it is due to barium ion confirming Ba2+ is present in the test sample
• The formation of white precipitate at this stage is CaC2O4 which is a strong indication of Ca2+ is present in the test solution
• If the solution imparts brick-red color to the flame, it is due to calcium ions confirming Ca2+ is present in the test sample
• If the solution imparts intense yellow color flame it confirms Na+ is present in the test solution, and purple or lilac color to the flame confirms K+ is present in the test solution