⚗️ Reactivity of Metals
- Metals react to form positive ions (cations) by losing electrons.
- More reactive metals lose electrons more easily.
Reactivity Series (most → least reactive):
Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Zinc (Zn) > Iron (Fe) > Tin (Sn) > Lead (Pb) > Copper (Cu) > Silver (Ag) > Gold (Au)
💡 Uses:
- Highly reactive metals like potassium are stored in oil to prevent reactions with air/water.
- Low reactivity metals like gold don’t corrode → ideal for jewelry.
🧪 Acid-Base Reactions
- Acids produce H⁺ ions in solution.
- Bases neutralise acids.
Neutralisation:
Acid + Base → Salt + Water
Examples:
- HCl + NaOH → NaCl + H₂O
- H₂SO₄ + Mg(OH)₂ → MgSO₄ + 2H₂O
💡 Indicators:
- Litmus: Red in acid, blue in alkali
- Phenolphthalein: Colourless in acid, pink in alkali
🧫 Acid + Metal Reactions
Acid + Metal → Salt + Hydrogen gas
Example:
- 2HCl + Mg → MgCl₂ + H₂
- Reactivity depends on metal in the reactivity series.
Observation: fizzing (H₂ gas), metal disappears, salt forms in solution.
🧲 Acid + Metal Oxide / Hydroxide
- Metal oxides and hydroxides are alkaline → neutralise acids.
- Acid + Metal Oxide → Salt + Water
- Acid + Metal Hydroxide → Salt + Water
Example:
- H₂SO₄ + CuO → CuSO₄ + H₂O
🔋 Electrolysis
Electrolysis = breaking down an ionic compound using electricity.
How it works:
- Compound is molten or dissolved in water → ions free to move
- Positive ions (cations) → cathode (negative electrode)
- Negative ions (anions) → anode (positive electrode)
Example: Electrolysis of molten NaCl:
- Cathode: Na⁺ → Na (metal forms)
- Anode: Cl⁻ → Cl₂ (gas forms)
💡 Electrolysis of aqueous solutions:
- H⁺ and OH⁻ ions also present → can compete with metal/non-metal ions.
- Hydrogen usually produced at cathode if metal less reactive than hydrogen.
- Oxygen produced at anode if halides not present.
⚡ Extraction of Metals
Metal reactivity determines extraction method:
| Reactivity | Extraction Method | Example |
|---|---|---|
| Very reactive (K, Na, Ca, Mg, Al) | Electrolysis of molten compounds | Al from Al₂O₃ |
| Less reactive (Zn, Fe, Pb) | Reduction with carbon | Fe from Fe₂O₃, Zn from ZnO |
| Least reactive (Cu, Ag, Au) | Found as native metals | Cu, Ag, Au |
💡 Tip: Carbon can only reduce metals less reactive than itself.
🧪 Displacement Reactions
- A more reactive metal will displace a less reactive metal from a compound.
Example:
- Zn + CuSO₄ → ZnSO₄ + Cu
- Observations: blue solution turns colourless (Cu²⁺ → Zn²⁺), copper solid forms.
🌿 Acid-Base and Salt Formation
- Soluble salts: can be made using acid + metal/metal oxide/alkali
- Crystallisation: evaporate water → salt crystals form
- Precipitation: mix soluble salts → insoluble salt forms
Example:
- BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl (BaSO₄ is insoluble → precipitate)
💧 pH Scale & Neutralisation
- pH scale: 0 → 14 (0 = strong acid, 7 = neutral, 14 = strong alkali)
- Strong acids ionise completely (e.g., HCl)
- Weak acids only partially ionise (e.g., CH₃COOH)
Calculating pH:
- Strong acids: pH = −log₁₀[H⁺]
