Manganese Properties Oxidation States And Reactions
Introduction
Manganese (Mn), atomic number 25, is a versatile transition metal. It exhibits multiple oxidation states from +2 to +7, leading to a rich redox chemistry and diverse industrial applications.
Occurrence & Extraction
Manganese is primarily found in minerals like pyrolusite (MnO₂) and rhodochrosite (MnCO₃). Extraction involves reduction of MnO₂ with carbon or aluminum:
3 MnO₂ + 4 Al → 3 Mn + 2 Al₂O₃ MnO₂ + C → MnO + CO₂
Physical Properties
- Silvery–gray, hard, brittle metal
- Melting point: 1246 °C; boiling point: 2061 °C
- Density: 7.21 g cm⁻³
- Paramagnetic due to unpaired d‑electrons
Chemical Properties
- With oxygen: Forms MnO₂ and higher oxides on heating.
- With acids: Mn + 2 HCl → MnCl₂ + H₂; oxidizing acids convert Mn²⁺ to higher oxidation states.
- With alkalis: Forms manganates (green) and permanganates (purple) under oxidizing conditions:
3 MnO₂ + 6 OH⁻ → 2 MnO₄²⁻ + MnO₂ + 3 H₂O 2 MnO₄²⁻ + 2 H₂O → 2 MnO₄⁻ + 4 OH⁻
Oxidation States
Manganese exhibits common oxidation states:
| Oxidation State | Species | Color |
|---|---|---|
| +2 | Mn²⁺ | Pale pink |
| +4 | MnO₂ | Black |
| +6 | MnO₄²⁻ (manganate) | Green |
| +7 | MnO₄⁻ (permanganate) | Purple |
Key Reactions
Formation of Potassium Permanganate
2 KMnO₄ → K₂MnO₄ + MnO₂ + O₂ (on heating) 3 K₂MnO₄ + 2 H₂O + O₂ → 2 KMnO₄ + 4 KOH
Redox with Permanganate
In acidic medium:
2 MnO₄⁻ + 16 H⁺ + 10 e⁻ → 2 Mn²⁺ + 8 H₂O
In neutral/alkaline medium:
3 MnO₄⁻ + 2 H₂O → 2 MnO₄²⁻ + MnO₂ + 4 OH⁻
Applications
- Potassium permanganate as oxidizing agent in analytical chemistry
- Alloying element in steel to improve strength and corrosion resistance
- Catalyst in organic oxidation reactions
- Dry cell battery cathode material (MnO₂)
- Water treatment and disinfection
Conclusion
Manganese’s multiple oxidation states enable diverse redox chemistry, underpinning its roles in materials, catalysis, and analytical techniques. Understanding its properties and reactions is essential for inorganic and industrial chemistry.
