Reactivity Series and Extraction of Metals
The Reactivity Series
The reactivity series is a list of metals arranged in order of how readily they react. More reactive metals lose electrons more easily.
Most reactive → Least reactive:
Potassium (K) > Sodium (Na) > Lithium (Li) > Calcium (Ca) > Magnesium (Mg) > Aluminium (Al) > Carbon (C) > Zinc (Zn) > Iron (Fe) > Hydrogen (H) > Copper (Cu) > Silver (Ag) > Gold (Au) > Platinum (Pt)
Carbon and hydrogen are included because they are used as reference points. Carbon is used to extract some metals; hydrogen helps classify acid reactions.
Displacement Reactions
A more reactive metal displaces a less reactive metal from its compound. This is a key application of the reactivity series.
Examples:
Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)
Magnesium is more reactive than copper, so it displaces copper from solution. You would see the blue solution lose its colour and a brown/orange solid (copper) deposit.
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
But: Cu(s) + ZnSO₄(aq) → no reaction (copper is less reactive than zinc)
Thermit Reaction
2Al(s) + Fe₂O₃(s) → Al₂O₃(s) + 2Fe(l)
Aluminium is more reactive than iron, so it displaces iron. This reaction is extremely exothermic and is used to weld railway tracks.
Reactions with Acids
Metals above hydrogen in the reactivity series react with dilute acids to produce a salt and hydrogen gas.
metal + acid → salt + hydrogen
Examples:
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Metals below hydrogen (copper, silver, gold, platinum) do not react with dilute acids.
Reactions with Water
The most reactive metals react with cold water:
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
Less reactive metals (e.g. magnesium) react very slowly with cold water but react with steam:
Mg(s) + H₂O(g) → MgO(s) + H₂(g)
Metals below hydrogen do not react with water.
Oxidation and Reduction (Redox)
In displacement and extraction reactions:
- The more reactive metal is oxidised (loses electrons)
- The less reactive metal is reduced (gains electrons)
These reactions are called redox reactions because oxidation and reduction happen simultaneously.
Zn → Zn²⁺ + 2e⁻ (oxidation — Zn loses electrons)
Cu²⁺ + 2e⁻ → Cu (reduction — Cu²⁺ gains electrons)
Extraction of Metals
The method used to extract a metal from its ore depends on the metal's position in the reactivity series.
Metals Below Carbon: Reduction with Carbon
Metals less reactive than carbon (zinc, iron, copper, lead, tin) can be extracted by heating with carbon (often in the form of coke/charcoal). Carbon is cheaper and more reactive, so it reduces the metal oxide.
2Fe₂O₃(s) + 3C(s) → 4Fe(l) + 3CO₂(g)
ZnO(s) + C(s) → Zn(s) + CO(g)
Iron is extracted industrially in a blast furnace. Iron ore (haematite, Fe₂O₃), coke (carbon) and limestone are fed in. The carbon burns to form CO, which reduces the iron oxide.
Metals Above Carbon: Electrolysis
Metals more reactive than carbon (potassium, sodium, lithium, calcium, magnesium, aluminium) cannot be reduced by carbon. They must be extracted by electrolysis of their molten compounds, which is expensive because:
- The compound must be melted (high energy input)
- Large amounts of electricity are needed
- The process runs continuously
Aluminium is extracted by electrolysis of molten aluminium oxide (Al₂O₃) dissolved in cryolite (to lower the melting point from ~2050°C to ~950°C).
At cathode: Al³⁺ + 3e⁻ → Al
At anode: 2O²⁻ → O₂ + 4e⁻
The carbon anodes must be replaced regularly because the oxygen produced reacts with them to form CO₂.
Summary
| Position in reactivity series | Extraction method | Examples |
|---|---|---|
| Above carbon (very reactive) | Electrolysis | K, Na, Li, Ca, Mg, Al |
| Below carbon | Reduction with carbon | Zn, Fe, Cu, Pb, Sn |
| Very unreactive | Found native (uncombined) | Gold, platinum |
Exam Tips
- Learn the reactivity series in order — a mnemonic helps (e.g. "Please Stop Letting Cows Moo And Chew Zesty Ironed Hay Considering Silver Gets Pricey")
- Be able to predict whether a displacement reaction will occur by comparing positions
- Know why electrolysis is more expensive than carbon reduction
- Understand the terms oxidation and reduction in terms of electron transfer