Most metals are found in nature as ORES — rocks containing metal compounds (usually oxides, sulfides or carbonates) rather than pure metals.
Only very UNREACTIVE metals (gold, platinum, silver) are found as pure elements in nature — they are too unreactive to form compounds with oxygen or sulfur.
All other metals must be EXTRACTED from their ores — the metal compound must be converted back to a pure metal.
The REACTIVITY of the metal determines the EXTRACTION METHOD:
VERY REACTIVE metals (K, Na, Ca, Mg, Al) — cannot be extracted by carbon reduction because they are more reactive than carbon. Must use ELECTROLYSIS of molten compounds.
MODERATELY REACTIVE metals BELOW carbon in the series (Zn, Fe, Sn, Pb) — can be extracted by heating their oxide with CARBON (reduction).
UNREACTIVE metals (Cu, Ag, Au) — found native (as pure elements) or can be extracted by simple reduction or displacement.
Reduction with Carbon — Blast Furnace
REDUCTION WITH CARBON (also called SMELTING) works for metals below carbon in the reactivity series.
Carbon displaces these metals from their oxides because carbon is MORE REACTIVE than these metals.
IRON FROM IRON OXIDE (Blast Furnace):
Iron ore (mainly haematite: Fe₂O₃) is heated with coke (carbon) and limestone in a blast furnace.
Carbon reacts with oxygen to form carbon dioxide:
C + O₂ → CO₂
CO₂ then reacts with more carbon to form carbon monoxide:
CO₂ + C → 2CO
Carbon monoxide REDUCES iron oxide to iron:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
Molten iron sinks to the bottom of the furnace and is tapped off.
ZINC EXTRACTION:
ZnO + C → Zn + CO₂
ALUMINIUM CANNOT be extracted this way — it is above carbon in the reactivity series and must use electrolysis.
Electrolysis for Reactive Metals
ELECTROLYSIS is used for metals that are MORE REACTIVE than carbon (K, Na, Li, Ca, Mg, Al).
These metals form very stable compounds — carbon cannot reduce them.
Instead, electrical energy is used to decompose the molten compound.
ALUMINIUM EXTRACTION (Hall-Héroult process):
Aluminium oxide (Al₂O₃) — also called alumina — is dissolved in molten cryolite (to lower the melting point from ~2000°C to ~950°C).
Electrolysis takes place:
At CATHODE (negative): Al³⁺ + 3e⁻ → Al (aluminium deposited)
At ANODE (positive): O²⁻ → O₂ (oxygen gas produced)
Molten aluminium sinks to the bottom and is tapped off.
Why electrolysis is expensive:
Huge amounts of ELECTRICAL ENERGY needed.
The process must run continuously at high temperatures.
The carbon anodes react with oxygen and must be REPLACED regularly.
This is why aluminium was once more expensive than gold — before cheap electricity, it was extremely difficult to extract.
⚠️ Common Mistake
Aluminium is above carbon in the reactivity series — carbon CANNOT reduce aluminium oxide. Students often try to apply carbon reduction to all metals. Only metals BELOW carbon in the reactivity series can be extracted by carbon reduction. Metals above carbon (including aluminium) require electrolysis.
📐 Key Equations
Fe₂O₃ + 3CO → 2Fe + 3CO₂ (iron extraction)
ZnO + C → Zn + CO₂
2Al₂O₃ → 4Al + 3O₂ (electrolysis of aluminium oxide)
📌 Key Note
Extraction method depends on reactivity. Above carbon in series → electrolysis (Al, Mg, Na etc.). Below carbon → reduction with carbon/CO (Fe, Zn etc.). Unreactive metals → found native or simple reduction. Iron: blast furnace with CO. Aluminium: electrolysis of molten Al₂O₃ in cryolite.
🎯 Matching Activity — Match the Metal to its Extraction Method
Match each metal to how it is extracted from its ore. — drag the symbols on the right to match the component names on the left.
Iron
Drop here
Aluminium
Drop here
Gold
Drop here
Zinc
Drop here
Sodium
Drop here
Electrolysis of molten NaCl — far too reactive for carbon reduction
Electrolysis of molten Al₂O₃ in cryolite — above carbon in reactivity series
Found as the pure element — too unreactive to form stable compounds
Reduced with carbon monoxide in a blast furnace — below carbon in reactivity series
Heated with carbon/coke — ZnO + C → Zn + CO₂
⭐ Higher Tier Only
Evaluate economic and environmental factors: energy cost of electrolysis vs smelting, environmental impact of mining, transportation costs. Compare traditional vs alternative methods (phytomining, bioleaching) in terms of speed, cost, environmental impact and suitability for ore grade.
🎯 Test Yourself
Question 1 of 2
1. Why is aluminium extracted by electrolysis rather than by reduction with carbon?
2. Carbon monoxide reduces iron oxide in the blast furnace. What type of reaction is this?
⭐ How Well Do You Understand This Topic?
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