Extraction of Metals and Reduction

This lesson covers the extraction of metals from their ores as required by the AQA GCSE Combined Science Trilogy specification (8464). You need to understand why different metals require different extraction methods, explain reduction with carbon, and discuss the economic and environmental implications.

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Metals and Their Ores

Most metals are found in the Earth's crust combined with other elements as compounds in ores. An ore is a rock containing enough metal to make extraction worthwhile.

Metal	Common Ore	Formula of Compound
Iron	Haematite	Fe₂O₃
Aluminium	Bauxite	Al₂O₃
Copper	Chalcopyrite	CuFeS₂
Zinc	Sphalerite	ZnS
Lead	Galena	PbS

Exam Tip: Only very unreactive metals such as gold and platinum are found native (uncombined) in the ground. All other metals are found as compounds in ores.

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Choosing the Extraction Method

The position of a metal in the reactivity series determines how it is extracted from its ore.

flowchart TD
    A["Metal ore"] --> B{"Is the metal more reactive<br/>than carbon?"}
    B -- "Yes" --> C["Extract by<br/>ELECTROLYSIS<br/>(e.g. aluminium, sodium, potassium)"]
    B -- "No" --> D{"Is the metal less reactive<br/>than carbon?"}
    D -- "Yes" --> E["Extract by<br/>REDUCTION WITH CARBON<br/>(e.g. iron, zinc, lead)"]
    D -- "No" --> F["Found NATIVE<br/>(e.g. gold, platinum)"]

    style C fill:#1565c0,color:#fff
    style E fill:#2e7d32,color:#fff
    style F fill:#f9a825,color:#000

Key Rules

Position Relative to Carbon	Extraction Method	Examples
Above carbon in the reactivity series	Electrolysis	Potassium, sodium, calcium, aluminium
Below carbon in the reactivity series	Reduction with carbon	Zinc, iron, tin, lead
Very unreactive	Found as the native metal	Gold, platinum

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Reduction With Carbon

Metals below carbon in the reactivity series can be extracted by heating their oxide with carbon (often in the form of coke or charcoal). Carbon is more reactive than the metal, so it removes the oxygen from the metal oxide.

General Equation

$\text{metal oxide} + \text{carbon} \rightarrow \text{metal} + \text{carbon dioxide}$metal oxide+carbon→metal+carbon dioxide

Example — Extracting Iron

Iron is extracted from haematite (Fe₂O₃) in a blast furnace. The carbon (coke) removes the oxygen:

$2\text{Fe}_2\text{O}_3(s) + 3\text{C}(s) \rightarrow 4\text{Fe}(l) + 3\text{CO}_2(g)$2Fe2​O3​(s)+3C(s)→4Fe(l)+3CO2​(g)

• The iron oxide is reduced (it loses oxygen).
• The carbon is oxidised (it gains oxygen).

Example — Extracting Zinc

$2\text{ZnO}(s) + \text{C}(s) \rightarrow 2\text{Zn}(s) + \text{CO}_2(g)$2ZnO(s)+C(s)→2Zn(s)+CO2​(g)

Example — Extracting Lead

$2\text{PbO}(s) + \text{C}(s) \rightarrow 2\text{Pb}(l) + \text{CO}_2(g)$2PbO(s)+C(s)→2Pb(l)+CO2​(g)

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Why Aluminium Cannot Be Extracted With Carbon

Aluminium is above carbon in the reactivity series. Carbon is not reactive enough to remove the oxygen from aluminium oxide. Therefore, aluminium must be extracted by electrolysis of molten aluminium oxide (dissolved in cryolite to lower the melting point and reduce energy costs).

Exam Tip: If you are asked why electrolysis is used for aluminium, the key point is that aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide.

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The Blast Furnace (Iron Extraction)

The blast furnace operates continuously and uses these raw materials:

Raw Material	Purpose
Iron ore (haematite, Fe₂O₃)	Source of iron
Coke (carbon)	Fuel and reducing agent
Limestone (CaCO₃)	Removes impurities (forms slag)
Hot air	Provides oxygen for combustion of coke

Reactions Inside the Blast Furnace

1. Coke burns in hot air: $\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)$C(s)+O2​(g)→CO2​(g)
2. Carbon dioxide reacts with more coke: $\text{CO}_2(g) + \text{C}(s) \rightarrow 2\text{CO}(g)$CO2​(g)+C(s)→2CO(g)
3. Carbon monoxide reduces the iron oxide: $\text{Fe}_2\text{O}_3(s) + 3\text{CO}(g) \rightarrow 2\text{Fe}(l) + 3\text{CO}_2(g)$Fe2​O3​(s)+3CO(g)→2Fe(l)+3CO2​(g)

The molten iron sinks to the bottom and is tapped off. The slag (calcium silicate) floats on top and is used for road building.

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Economic and Environmental Considerations

Factor	Detail
Cost of electrolysis	Very expensive due to high electricity requirements; used only when necessary
CO₂ emissions	Blast furnace produces large amounts of CO₂, contributing to climate change
Mining	Open-cast mining destroys habitats and landscapes
Recycling	Recycling metals uses far less energy than extraction — e.g. recycling aluminium saves ~95% of the energy needed for primary extraction

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Common Mistakes

Mistake	Correction
Saying "carbon is used to extract aluminium"	Aluminium is above carbon in the reactivity series, so electrolysis is required
Forgetting that carbon is oxidised during extraction	Carbon gains oxygen → it is oxidised; the metal oxide loses oxygen → it is reduced
Confusing ore with metal	An ore is a rock containing a metal compound — it is NOT the pure metal
Thinking all metals are extracted the same way	The method depends on the metal's position in the reactivity series relative to carbon

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Worked Example

Question: Explain why iron can be extracted by reduction with carbon, but aluminium cannot.

Answer:

1. Iron is below carbon in the reactivity series.
2. Carbon is more reactive than iron, so it can remove the oxygen from iron oxide: 2Fe₂O₃ + 3C → 4Fe + 3CO₂.
3. Aluminium is above carbon in the reactivity series.
4. Carbon is not reactive enough to remove the oxygen from aluminium oxide.
5. Therefore, aluminium must be extracted by electrolysis of molten aluminium oxide.

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Summary

• Metals are usually found as compounds in ores in the Earth's crust; only very unreactive metals are found native.
• The extraction method depends on the metal's position in the reactivity series relative to carbon.
• Metals below carbon are extracted by reduction with carbon — the carbon removes oxygen from the metal oxide.
• Metals above carbon require electrolysis because carbon cannot reduce their oxides.
• In reduction with carbon, the metal oxide is reduced (loses oxygen) and the carbon is oxidised (gains oxygen).
• Recycling metals conserves resources and saves energy compared to extraction from ores.

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Extended Worked Examples