Iron and d-Block Elements

Iron

Iron is a d-block element: Fe [Ar]3d⁶4s².

• It shows oxidation states +2 and +3 in compounds.
• Fe + 2HCl → FeCl₂ + H₂↑ (Fe²⁺ forms).
• 2Fe + 3Cl₂ → 2FeCl₃.
• Concentrated HNO₃ and H₂SO₄ passivate iron in the cold.
• Fe + CuSO₄ → FeSO₄ + Cu.
• In the blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂.

Its ores: magnetite Fe₃O₄, hematite Fe₂O₃, pyrite FeS₂.

Cast iron: 2-6% C, steel: less than 2% C (alloys of Fe).

Qualitative reactions

• Fe³⁺ + KSCN → blood-red solution.
• Fe²⁺ + K₃[Fe(CN)₆] → blue precipitate: Fe²⁺: Turnbull's blue.
• Fe³⁺ + K₄[Fe(CN)₆] → blue precipitate: Fe³⁺: Prussian blue.

Colors of ions

Ion	Color
Cu²⁺	Cu²⁺ is blue in solution
Cr³⁺	green
MnO₄⁻	purple
Cr₂O₇²⁻	orange
CrO₄²⁻	yellow
Fe³⁺	yellow-brown
Fe²⁺	pale green

Additional notes

• Cu, Cr, Mn: variable valency, with different colors.
• Fe(OH)₂ is white (turns into brown Fe(OH)₃ in air). Fe(OH)₃ is a brown precipitate.
• Zn and Cr(OH)₃ are amphoteric. Cu(OH)₂ is a blue precipitate; when heated it gives CuO (black).
• Corrosion of iron: rusting in moist air (Fe₂O₃·nH₂O).