Contents
1. The Reactivity Series
Metals are arranged in order of decreasing reactivity. The more reactive a metal, the more easily it loses electrons to form positive ions.
| Metal | Symbol | Relative reactivity |
|---|---|---|
| Potassium | K | Most reactive |
| Sodium | Na | ↕ |
| Calcium | Ca | ↕ |
| Magnesium | Mg | ↕ |
| Aluminium | Al | ↕ |
| Zinc | Zn | ↕ |
| Iron | Fe | ↕ |
| Tin | Sn | ↕ |
| Lead | Pb | ↕ |
| Hydrogen | H | ↕ (reference point) |
| Copper | Cu | ↕ |
| Silver | Ag | ↕ |
| Gold | Au | Least reactive |
Please Send Charlie's Monkeys Along Zebra In The Little Compound's Stable Ground — K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Ag, Au.
2. Reactions of Metals
| Reaction | Very reactive (K, Na, Ca) | Moderately reactive (Mg, Al, Zn, Fe) | Unreactive (Cu, Ag, Au) |
|---|---|---|---|
| With cold water | Vigorous; H₂ + metal hydroxide | Very slow or none | No reaction |
| With steam | Explosive (not done safely) | H₂ + metal oxide | No reaction |
| With dilute acid | Explosive | H₂ + salt | No reaction |
| With oxygen | Burns vigorously | Burns / tarnishes | Little or no reaction |
With acid: Mg + H₂SO₄ → MgSO₄ + H₂
With steam: Mg + H₂O → MgO + H₂
With oxygen: 2Mg + O₂ → 2MgO
3. Displacement Reactions
A more reactive metal will displace a less reactive metal from its salt solution. This is a redox reaction — the more reactive metal is oxidised (loses electrons); the less reactive metal ion is reduced (gains electrons).
Iron nail placed in copper sulfate solution:
Fe + CuSO₄(aq) → FeSO₄(aq) + Cu
Observation: blue solution fades; brown copper metal deposits on the iron nail; nail becomes coated in copper.
Fe is above Cu in the reactivity series → Fe displaces Cu. Fe is oxidised (0 → +2); Cu²⁺ is reduced (+2 → 0).
4. Extraction of Metals
The method used to extract a metal from its ore depends on its position in the reactivity series.
| Reactivity | Method of extraction | Examples |
|---|---|---|
| Very reactive (K, Na, Ca, Al) | Electrolysis of molten ore | Al from bauxite (Al₂O₃); Na from NaCl |
| Moderately reactive (Zn, Fe, Sn, Pb) | Reduction with carbon (coke) in a blast furnace | Fe from haematite (Fe₂O₃) |
| Low reactivity (Cu, Ag, Au) | Found native or simple reduction | Cu from CuO + carbon; Au found as pure metal |
Aluminium is more reactive than carbon — carbon cannot reduce Al₂O₃. Electrolysis must be used instead. This makes aluminium more expensive to extract than iron.
5. Corrosion and Rusting
Rusting is the corrosion of iron. It requires both oxygen AND water — neither alone causes rusting.
Equation: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O (hydrated iron(III) oxide = rust)
Preventing rusting
| Method | How it works |
|---|---|
| Painting / coating with plastic | Physical barrier — excludes water and oxygen |
| Galvanising (zinc coating) | Barrier + sacrificial protection (zinc is more reactive, corrodes first) |
| Sacrificial protection (zinc/magnesium block) | More reactive metal corrodes preferentially, protecting iron |
| Alloying with chromium (stainless steel) | Chromium oxide layer prevents further oxidation |
- Reactivity series order: K, Na, Ca, Mg, Al, (C), Zn, Fe, (H), Cu, Ag, Au. Must memorise.
- More reactive metal DISPLACES less reactive from solution. Less reactive = deposited as solid.
- Metals above carbon in reactivity series: extracted by electrolysis (Al, Na, K, Mg).
- Metals below carbon: extracted by reduction with carbon (Fe, Zn, Pb).
- Rusting: needs BOTH O2 AND H2O. Prevention: painting, oiling, galvanising (zinc), sacrificial protection.
- Sacrificial anode: Mg or Zn attached to iron structure. More reactive metal corrodes instead of iron.
6. Common Exam Traps
Iron in dry oxygen does not rust. Iron in boiled, sealed water (no dissolved oxygen) does not rust. Both conditions must be present. State both in the answer.
A less reactive metal cannot displace a more reactive one. Copper added to magnesium sulfate solution — no reaction. Only if the added metal is more reactive than the metal in solution will displacement occur.
Aluminium is actually very reactive, but a thin, tough layer of aluminium oxide (Al₂O₃) forms instantly on its surface and protects it from further reaction. This is why aluminium does not corrode visibly despite being above zinc in the reactivity series.
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Original study notes for Singapore students. Not affiliated with MOE, SEAB or Cambridge.