Analytical Chemistry: Group I & II Tests

Group (I) Analysis

• Pb²⁺ (Lead):
  • Main Test: Lead chloride (PbCl₂) forms a white precipitate when reacted with dilute hydrochloric acid (HCl).
  • Solubility: This precipitate is soluble in water.
  • Confirmatory Test: A bright yellow precipitate lead chromate (PbCrO₄) forms when lead is treated with potassium chromate (K₂CrO₄). A yellow precipitate of lead iodide (PbI₂) forms using potassium iodide (KI).

Group (II) Analysis

• Ag⁺ (Silver):

  • Main Test: Silver chloride (AgCl) forms a white precipitate with dilute HCl.
  • Solubility: This precipitate is insoluble in water.
  • Confirmatory Test: The precipitate is treated with a potassium chromate (K₂CrO₄) solution, forming a brick-red silver chromate (Ag₂CrO₄) precipitate. Treating with potassium iodide (KI) forms a yellowish precipitate of silver iodide (AgI). NH₃ can be used for a confirmation step.

• Hg₂²⁺ (Mercurous):

  • Main Test: Mercurous chloride (Hg₂Cl₂) forms a white precipitate which is insoluble in dilute HCl..
  • Confirmatory Test: Mercurous chromate (Hg₂CrO₄) forms a brown precipitate using potassium chromate (K₂CrO₄). Yellowish-green Hg₂I₂ (Mercurous iodide) precipitates using potassium iodide (KI).

• Cd²⁺ (Cadmium):

  • Main Test: Cadmium sulfide (CdS) forms a yellow precipitate reacting with dilute acid and hydrogen sulfide (H₂S).
  • Confirmatory Test: Cadmium hydroxide (Cd(OH)₂) is a white precipitate resulting from reacting cadmium with sodium hydroxide (NaOH). Turning to soluble Cd(NH₃)₄²⁺ complex when excess ammonia (NH₃) is added.

• Cu²⁺ (Copper):

  • Main Test: Copper sulfide (CuS) forms a black precipitate with dilute acid and H₂S;
  • Confirmatory Test: Copper hydroxide (Cu(OH)₂) forms a blue precipitate reacting with sodium hydroxide (NaOH). Turning to soluble [Cu(NH₃)₄]²⁺ complex when excess ammonia is used.

• Bi³⁺ (Bismuth):

  • Main Test: Bismuth sulfide (Bi₂S₃) form a brown precipitate reacting with dilute acid and hydrogen sulfide (H₂S).
  • Confirmatory Test: Bismuth hydroxide (Bi(OH)₃) is a white precipitate occurring when bismuth is treated with sodium hydroxide (NaOH). When excess ammonia is present, it becomes insoluble.

• Hg²⁺ (Mercuric):

  • Main Test: Mercuric sulfide (HgS) is a black precipitate when reacting with dilute acid and hydrogen sulfide (H₂S).
  • Confirmatory Test: Mercuric hydroxide (Hg(OH)₂) is a yellow precipitate when reacting solution with sodium hydroxide (NaOH).

Group (III) Analysis

• Al³⁺ (Aluminum):

  • Main Test: Aluminum hydroxide (Al(OH)₃) is a white, gelatinous precipitate forming when the solution is treated with excess ammonia until alkaline (NH₃) and then added with sodium hydroxide (NaOH).
  • Confirmatory Test: Aluminum phosphate (AlPO₄) forms a white gelatinous precipitate using sodium phosphate (Na₃PO₄).

• Cr³⁺ (Chromium):

  • Main Test: Chromium hydroxide (Cr(OH)₃) is a gray-green precipitate precipitating using excess ammonia and dilute acid.
  • Confirmatory Test: Chromium phosphate (CrPO₄) is a green precipitate formed with solution of sodium phosphate (Na₃PO₄).

Group (IV) Analysis

• Zn²⁺ (Zinc):

  • Main Test: Zinc sulfide (ZnS) forms a white precipitate reacting with H₂S in presence of excess ammonia.
  • Confirmatory Test: Zinc hydroxide (Zn(OH)₂) precipitates using sodium hydroxide (NaOH). Zinc cyanide (Zn(CN)₂) precipitate with potassium cyanide (KCN).

• Mn²⁺ (Manganese):

  • Main Test: Manganese sulfide (MnS) forms a buff precipitate reacting with H₂S in presence of excess ammonia and dilute acid
  • Confirmatory Test: Manganese hydroxide (Mn(OH)₂) is a buff precipitate formed reacting the solution with sodium hydroxide (NaOH).

• Ni²⁺ (Nickel):

  • Main Test: Nickel sulfide (NiS) forms a black precipitate reacting with H₂S in presence of excess ammonia and dilute acid.
  • Confirmatory Test: Nickel hydroxide (Ni(OH)₂) is a green precipitate when reacting solution with sodium hydroxide (NaOH). Nickel dimethylglyoximate ((C₈H₁₄N₄O₄Ni)) forms a red precipitate with dimethylglyoxime in ammonia.

Group (V) Analysis

• Ca²⁺ (Calcium):

  • Main Test: Calcium carbonate (CaCO₃) forms a white precipitate reacting with Ammonium carbonate ((NH₄)₂CO₃) in presence of excess ammonia.
  • Confirmatory Test: Calcium sulfate (CaSO₄) forms a white precipitate reacting with calcium sulfate (CaSO₄). Flame test - characteristic brick red.

• Ba²⁺ (Barium):

  • Main Test: Barium carbonate (BaCO₃) forms a white precipitate reacting with Ammonium carbonate.
  • Confirmatory Test: Barium sulfate (BaSO₄) forms a white precipitate using calcium sulfate (CaSO₄). Flame test- characteristic apple green.

• Sr²⁺ (Strontium):

  • Main Test: Strontium carbonate (SrCO₃) forms a white precipitate reacting with Ammonium carbonate ((NH₄)₂CO₃) in presence of excess ammonia
  • Confirmatory Test: Strontium sulfate (SrSO₄) forms a white precipitate, turning milky-white when boiling. Flame test – characteristic crimson/red.

Group (VI) Analysis

• Mg²⁺ (Magnesium):
  • Main Test: Magnesium phosphate (Mg₃(PO₄)₂) forms a white precipitate reacting with excess ammonia (NH₃), sodium hydroxide(NaOH) and sodium phosphate (Na₃PO₄).
  • Confirmatory Test: Magnesium carbonate (MgCO₃) forms a white precipitate using sodium carbonate (Na₂CO₃).

Group V - Analysis of Alkali Metals:

• K⁺ (Potassium):

  • Main Test: Sodium cobaltinitrite (Na₃[Co(NO₂)₆]) forms a yellow precipitate reacting with acetic acid and potassium.
  • Confirmatory Test: The solution is viewed through a flame test – produces a characteristic lilac/purple flame color

• NH₄⁺ (Ammonium):

  • Main Test: The addition of sodium hydroxide (NaOH) will liberate ammonia gas causing white fumes when moistened by hydrochloric acid (HCl)

• Na⁺ (Sodium):

  • Main Test: Sodium gives a characteristic Golden yellow in flame test.

Test your knowledge on Group I and II analysis in analytical chemistry. This quiz covers the main tests and confirmatory reactions for lead, silver, and mercurous ions. Understand the solubility and precipitation reactions fundamental to identifying these metals.