CHEM GROUP IV- V

• Group IV cations react with 1M solution of ammonium carbonate to form white precipitates
• The test must be carried out in neutral or alkaline solutions
• In the absence of ammonia or ammonium ions, magnesium will also be precipitated
• White precipitates formed with the group reagent are:

  • Barium carbonate (BaCO3)
  • Strontium carbonate (SrCO3)
  • Calcium carbonate (CaCO3)
• Barium (Ba) is a silver-white, malleable and ductile metal that reacts with water in humid air forming oxide or hydroxide
• Reactions of barium(II) ions:

  1. Ammonium carbonate solution - white precipitate of barium carbonate, soluble in acetic acid and dilute mineral acids

  2. Ammonium oxalate solution - white precipitate of barium oxalate

  3. Dilute sulfuric acid - forms a heavy, white, finely divided precipitate of barium sulfate

  4. Potassium chromate solution - yields a yellow precipitate of barium chromate
• Calcium is a silver-white, rather soft metal that decomposes water forming calcium hydroxide and hydrogen
• Reactions of calcium(II) ions:

  1. Ammonium carbonate solution - white amorphous precipitate of calcium carbonate

  2. Dilute sulfuric acid - white precipitate of calcium sulfate

  3. Ammonium oxalate solution - white precipitate of calcium oxalate
• Strontium is a silver-white, malleable and ductile metal with properties similar to barium
• Reactions of strontium(II) ions:

  1. Ammonium carbonate solution - white precipitate of strontium carbonate

  2. Dilute sulfuric acid - white precipitate of strontium sulfate

  3. Ammonium oxalate solution - white precipitate of strontium oxalate

  4. Potassium chromate solution - yellow precipitate of strontium chromate
• Group V cations do not react with hydrochloric acid, hydrogen sulfide, or ammonium sulfide
• Special reactions or flame tests can be used for their identification
• Magnesium displays similar reactions to Group IV cations but magnesium carbonate is soluble in the presence of ammonium salts
• Reactions of magnesium(II) ions:

  1. Sodium hydroxide solution - white precipitate of magnesium hydroxide

  2. Ammonium carbonate solution - white precipitate of basic magnesium carbonate

  3. Disodium hydrogen phosphate solution - white crystalline precipitate of magnesium ammonium phosphate
• Potassium is a soft, silver-white metal that decomposes water violently, evolving hydrogen and burning with a violet flame
• Reactions of potassium ions:

  1. Perchloric acid solution - white crystalline precipitate of potassium perchlorate
• Sodium is a silver-white soft metal that oxidizes rapidly in moist air
• Reactions of sodium(I) ions:

  1. Uranyl magnesium acetate solution - yellow crystalline precipitate sodium magnesium uranyl acetate
• Ammonium is derived from ammonia and the hydrogen ion
• Reactions of ammonium ions:

  1. Sodium hydroxide solution - ammonia gas is evolved on warming