Iron and its compounds
Iron links metallurgy, redox chemistry and qualitative analysis. Its common +2 and +3 oxidation states produce compounds with different colors and reactions.
Learning goals. Describe iron as a transition metal; distinguish Fe2+ and Fe3+; write precipitation and redox equations; outline blast-furnace extraction and steel production; and connect iron chemistry with corrosion control.
1. The metal and its reactions
Iron is a strong, dense, conductive transition metal. It commonly forms Fe2+ and Fe3+. Pure iron is relatively soft, while carbon and other alloying elements produce steels with controlled hardness, strength and corrosion resistance.
Iron burns in oxygen under suitable conditions and reacts with dilute non-oxidizing acids: Fe + 2HCl → FeCl2 + H2. Because iron is more active than copper, it displaces copper from solution: Fe + CuSO4 → FeSO4 + Cu. Conditions determine the oxidation state and product; do not assume every oxidant gives the same oxide or ion.
| Material | Composition idea | Typical consequence |
|---|---|---|
| Iron | Mostly Fe | Ductile but less hard |
| Low-carbon steel | Fe with a small carbon fraction | Strong and formable |
| Higher-carbon steel | More carbon in Fe | Harder but often less ductile |
| Corrosion-resistant steel | Fe alloyed with elements that support passivation | Improved resistance in suitable environments |
2. Oxides, hydroxides and salts
| Species | Oxidation state | Typical appearance |
|---|---|---|
| FeO | +2 | Black solid |
| Fe2O3 | +3 | Reddish-brown solid |
| Fe3O4 | Mixed +2/+3 | Black magnetic solid |
| Fe(OH)2 | +2 | Greenish precipitate that oxidizes in air |
| Fe(OH)3 | +3 | Reddish-brown precipitate |