Group 4 and 5

• Group IV cations

  Barium, Calcium, and Strontium
• Group 4 reagent

  1M solution of ammonium carbonate
• group 4 reaction:

  cations of the fourth group react neither with hydrochloric acid, hydrogen sulfide nor ammonium sulfide, but ammonium carbonate (in the presence of moderate amounts of ammonia or ammonium ions) forms white precipitates.
• Group 4

  The test has to be carried out in neutral or alkaline solutions. In the absence of ammonia or ammonium ions, magnesium will also be precipitated. The white precipitates formed with the group reagent are: (a) Barium carbonate - BaCO3, (b) Strontium carbonate - SrCO3, and (c) Calcium carbonate - CaCO3
• Group IV (Barium)


  a silver-white, malleable, and ductile metal, which is stable in dry air. It reacts with the water in humid air forming oxide or hydroxide. It melts at 710 °C.
• GROUP 4: Reactions of barium(Il) ions

  Use a 0.25M solution of barium chloride (BaCl2 ∙ 2 H2O), or barium nitrate [Ba(NO3 )2 ] for the study of these reactions.
• GROUP IV (Barium)

  1. Ammonium carbonate solution - white precipitate of barium carbonate, soluble in acetic acid and in dilute mineral acids: Ba2+ + CO3 2- ⇄ BaCO3 ↓
  2. Ammonium oxalate solution - white precipitate of barium oxalate: Ba2+ + (COO)2 2- ⇄ Ba(COO)2 ↓
  3. Dilute sulfuric acid – forms a heavy, white, finely divided precipitate of barium sulfate (BaSO4 ): Ba2+ + SO4 2- ⇄ BaS04 ↓
  4. Potassium chromate solution – yields a yellow precipitate of barium chromate, practically insoluble in water: Ba2+ + CrO4 2- ⇄ BaCrO4 ↓
• GROUP IV (Calcium)

  • a silver-white, rather soft metal. It melts at 845 °C. It is attacked by atmospheric oxygen and humidity when calcium oxide and/or calcium hydroxide is formed.
  • Calcium decomposes water forming calcium hydroxide and hydrogen.
• GROUP IV: reactions of calcium(II) ions

  • to study these reactions a 0.5 M solution of calcium chloride (CaCI2 ∙ 6 H2O) can be used.
• GROUP IV (Calcium)

  1. Ammonium carbonate solution - white amorphous precipitate of calcium carbonate: Ca2+ + CO3 2- ⇄ CaCO3 ↓
  2. Dilute sulfuric acid - white precipitate of calcium sulfate: Ca2+ + SO4 2- ⇄ CaS04 ↓
  3. Ammonium oxalate solution - white precipitate of calcium oxalate, immediately from concentrated and slowly from dilute solutions: Ca2+ + (COO)2 2- ⇄ Ca(COO)2 ↓
• GROUP IV (Strontium)

  • a silver-white, malleable and ductile metal. It melts at 771 °C. Its properties are similar to those of barium
• GROUP 4 (Strontium)

  Reactions of Strontium (lI) ions: For the study of these reactions a 0.25M solution of strontium chloride (SrCI2 ∙ 6 H2O), or strontium nitrate [Sr(NO3 )2 ] can be used.
• GROUP IV (Strontium)

  1. Ammonium carbonate solution - white precipitate of strontium carbonate: Sr2+ + CO3 2- ⇄ SrCO3 ↓
  2. Dilute sulfuric acid - white precipitate of strontium sulfate: Sr2+ + SO4 2- ⇄ SrSO4 ↓
  3. Ammonium oxalate solution - white precipitate of strontium oxalate: Sr2+ + (COO)2 2- ⇄ Sr(COO)2 ↓
  4. Potassium chromate solution - yellow precipitate of strontium chromate: Sr2+ + CrO4 2- ⇄ SrCrO4 ↓
• Group V Cations

  Magnesium, Sodium, Potassium, and Ammonium
• Group V reagent

  there is no common reagent for the cations of this group
• Group V (Group Reaction)

  • Cations do not react with hydrochloric acid
  • Cations do not react with hydrogen sulfide
  • Cations do not react with ammonium sulfide
  • Cations do not react with ammonium carbonate (in the presence of ammonium salts)
  • Special reactions or flame tests can be used for their identification
• Magnesium

  • Displays similar reactions to those of cations in the fourth group
  • Magnesium carbonate is soluble in the presence of ammonium salts, and therefore during the course of systematic analysis (when considerable amounts of ammonium salts are building up in the solution) magnesium will not precipitate with the cations of the fourth group
• GROUP V (Magnesium)

  • a white, malleable, and ductile metal. It melts at 650 °C
• GROUP V (Reactions of magnesium (II) ions)

  To study these reactions a 0.5M solution of magnesium chloride (MgCI2 ∙ 6 H2O), or magnesium sulfate (MgSO4 · 7 H2O) can be used.
• GROUP V (Magnesium)

  1. Sodium hydroxide solution - white precipitate of magnesium hydroxide, insoluble in excess reagent, but readily soluble in solutions of ammonium salts. Mg2+ + 2 OH- ⇄ Mg(OH)2 ↓
  2. Ammonium carbonate solution in the absence of ammonium salts a white precipitate of basic magnesium carbonate.
  3. Disodium hydrogen phosphate solution - white crystalline precipitate of magnesium ammonium phosphate [Mg(NH4 )PO4 ∙ 6H2O] in the presence of ammonium chloride (to prevent precipitation of magnesium hydroxide) and ammonia solutions.
• GROUP V (Potassium)

  • a soft, silver-white metal. Potassium melts at 63.5 °C. It remains unchanged in dry air, but is rapidly oxidized in moist air, becoming covered with a blue film the metal decomposes water violently, evolving hydrogen and burning with a violet flame.
• GROUP V (Reactions of Potassium ions)

  A M solution of potassium chloride, KCl, can be used for these tests.
• GROUP V (Potassium)

  1. Perchloric acid solution (HCIO4 ) -white crystalline precipitate of potassium perchlorate KCIO4 from moderately dilute solutions. K+ +ClO4 - ⇄ KCI04 ↓
• GROUP V (Sodium)

  • a silver-white soft metal melting at 97 C. It oxidizes rapidly in moist air and is therefore kept under liquid paraffin.
• GROUP V (Reactions of sodium(I) ions)

  • To study these reactions a M solution of sodium chloride, NaCl, can be used
• group 5 (Sodium)

  1. Uranyl magnesium acetate solution - yellow, crystalline precipitate of sodium magnesium uranyl acetate[NaMg(UO2 )3 (CH3COO)9 · 9 H2O] from concentrated solutions. The addition of about one-third volume of alcohol helps the precipitation: Na+ + Mg2+ + 3 UO2 2+ + 9 CH3COO- ⇄ NaMg(U02 )3 (CH3COO)9 ↓
• GROUP V (Ammonium)

  • derived from ammonia, NH3, and the hydrogen ion H+
  • The characteristics of these ions are similar to those of alkali metal ions. By electrolysis with a mercury cathode, ammonium amalgam can be prepared, which has similar properties to the amalgams of sodium or potassium.
• GROUP V (Reactions of ammonium ions)

  • To study these reactions a M solution of ammonium chloride NH4Cl can be used.
• GROUP V (Ammonium)

  1. Sodium hydroxide solution - ammonia gas is evolved on warming.NH4+ + OH- ⇄ NH3 ↑ + H2O
• Identifying ammonia gas

  • Odor (cautiously smell the vapor after removing the test tube or small beaker from the flame)
  • Formation of white fumes of ammonium chloride when a glass rod moistened with concentrated hydrochloric acid is held in the vapor
  • Turning moistened red litmus paper blue or turmeric paper brown
  • Ability to turn filter paper moistened with mercury(I) nitrate solution black
  • Filter paper moistened with a solution of manganese (II) chloride and hydrogen peroxide gives brown color, due to the oxidation of manganese by the alkaline solution thus formed