2.5.1Inorganic Chemistry
Sources of Metals — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 5 parts Lesson 20 of 52
Section 1 of 5Ores and Native Metals
Most metals are found combined with other elements, so they must be extracted from their compounds.
Ore
- A rock containing enough of a metal compound to make extracting the metal worthwhile.
Oxide ores
- Many metal ores are oxides, such as haematite, which contains iron(III) oxide, and bauxite, which contains aluminium oxide.
Unreactive metals
- Gold and platinum occur as uncombined elements because they are too unreactive to combine with other substances.
Reduction
- Extracting a metal from an oxide ore usually involves reduction, because oxygen is removed from the metal oxide.
Method depends on reactivity
- The extraction method depends on how reactive the metal is and where it sits in the reactivity series.
Section 2 of 5Extraction Methods
1
Metals above carbon cannot be reduced by carbon, so their ores must be broken down by electrolysis.
2
Metals below carbon can have their oxides reduced by heating them with carbon, which is a cheaper process.
3
Electrolysis needs large amounts of electricity, which makes the extraction of very reactive metals expensive.
4
Unreactive metals such as gold and silver do not need chemical extraction, because they are found uncombined.
| Position in series | Example metals | Extraction method |
|---|---|---|
| Above carbon | Potassium, sodium, aluminium | Electrolysis of the molten compound |
| Below carbon | Zinc, iron, copper | Heating the oxide with carbon or carbon monoxide |
| Least reactive | Gold, silver | Found uncombined and mined directly |
Section 3 of 5Blast Furnace and Aluminium
Blast Furnace and Aluminium
Iron in a blast furnace
- Haematite is reduced by carbon monoxide made from coke, with limestone removing silicon dioxide impurities as slag.
Carbon monoxide
- Coke burns in hot air to form carbon dioxide, which is reduced to carbon monoxide by more coke.
Aluminium
- Aluminium oxide dissolved in molten cryolite is electrolysed, because carbon cannot reduce aluminium oxide.
Cost
- The electrolysis of aluminium oxide is expensive, because it uses large amounts of electricity.
Section 4 of 5Worked Example
Question Explain why aluminium is extracted by electrolysis, while iron is extracted by reduction with carbon.
- Aluminium is above carbon in the reactivity series, so carbon cannot remove oxygen from aluminium oxide.
- Iron is below carbon in the series, so carbon can remove oxygen from iron(III) oxide and leave molten iron.
- Electrolysis supplies electrons directly, which reduces aluminium ions to aluminium when carbon is not strong enough to do so.
Answer
- Aluminium is more reactive than carbon, so it must be extracted by electrolysis;
- iron is less reactive than carbon, so carbon can reduce its oxide.
Section 5 of 5Exam Checklist & Tips
2.5.1 – Key Points for the Exam
- Ore A rock containing a metal compound in sufficient quantity to make extraction worthwhile.
- Haematite An iron ore containing iron(III) oxide, Fe₂O₃.
- Bauxite The main ore of aluminium, which contains aluminium oxide.
- Reduction The removal of oxygen from a compound.
- Blast furnace A large furnace in which iron is extracted from its ore by reduction with carbon monoxide.
Common Mistakes
- Saying gold is extracted by reduction; gold occurs uncombined and is mined directly.
- Using the word ore to mean any rock containing a metal;
- an ore must contain enough metal to be worth extracting.
- Assuming carbon can reduce aluminium oxide; aluminium is above carbon in the reactivity series.
- Stating that the blast furnace produces pure iron; the iron is impure and the slag is removed separately.
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