Chemical Properties of Metals
📚 Key Concepts
🔹 Real-Life Example
When you leave an iron nail outside in the rain, it slowly turns reddish-brown (rust). When you burn magnesium ribbon, it produces a brilliant white light (used in old camera flashes). When you drop sodium in water, it fizzes violently and may even catch fire! These dramatic reactions show how metals interact with their environment.
🧪 Important Reactions
🔸 Reaction with Oxygen
General Equation: Metal + Oxygen → Metal Oxide
Examples:
- Magnesium: 2Mg + O₂ → 2MgO (brilliant white light)
- Iron: 4Fe + 3O₂ → 2Fe₂O₃ (rust formation)
- Copper: 2Cu + O₂ → 2CuO (black coating on copper vessels)
- Aluminum: 4Al + 3O₂ → 2Al₂O₃ (protective oxide layer)
Reactivity Order: K > Na > Ca > Mg > Al > Zn > Fe > Cu > Ag > Au
🔸 Reaction with Water
General Equation: Metal + Water → Metal Hydroxide + Hydrogen
Categories:
- React with cold water: K, Na, Ca
- Sodium: 2Na + 2H₂O → 2NaOH + H₂ (violent reaction, heat produced)
- Calcium: Ca + 2H₂O → Ca(OH)₂ + H₂ (less violent)
- React with steam: Mg, Al, Zn, Fe
- Magnesium: Mg + H₂O → MgO + H₂ (with steam)
- Iron: 3Fe + 4H₂O → Fe₃O₄ + 4H₂ (red hot iron with steam)
- No reaction: Cu, Ag, Au (noble metals)
🔸 Reaction with Acids
General Equation: Metal + Acid → Salt + Hydrogen
Examples:
- Zinc: Zn + H₂SO₄ → ZnSO₄ + H₂ (lab method for H₂ production)
- Magnesium: Mg + 2HCl → MgCl₂ + H₂ (rapid effervescence)
- Iron: Fe + 2HCl → FeCl₂ + H₂ (slow reaction)
Note: Cu, Ag, Au don’t react with dilute acids (noble metals)
Test for Hydrogen: Burning splinter near gas → “Pop” sound
🔸 Metal Oxides – Basic Nature
- Metal oxides are generally basic
- Turn red litmus blue
- React with acids to form salt and water
Examples:
- Sodium oxide: Na₂O + H₂O → 2NaOH (strong base)
- Magnesium oxide: MgO + H₂O → Mg(OH)₂ (milk of magnesia)
🔸 Amphoteric Oxides
Some metal oxides show both acidic and basic properties:
- Aluminum oxide (Al₂O₃)
- Zinc oxide (ZnO)
Example Reactions:
- As base: ZnO + 2HCl → ZnCl₂ + H₂O
- As acid: ZnO + 2NaOH → Na₂ZnO₂ + H₂O