Extraction of Metals

CIE IGCSE Chemistry· 9.6· 45 min read

1. 1. Extraction Method and Reactivity Series★★☆☆☆⏱ 10 min

📘 Definition

Ore

A naturally occurring rock containing sufficient metal compound to make extraction of the metal economically viable.

The method used to extract a metal from its ore depends entirely on its position in the reactivity series. Less reactive metals can be extracted with simple physical purification, moderately reactive metals by reduction with carbon, and highly reactive metals by electrolysis of their molten ores.

Metals below copper (e.g. gold, silver): found native (uncombined), require only physical purification
Metals between zinc and copper: reduced by heating with carbon or carbon monoxide
Metals above zinc (e.g. aluminium, magnesium, sodium): require electrolysis of molten compounds, as carbon cannot displace them

📐 Worked Example

Metal X does not react with dilute acids and is found uncombined in rock deposits. State the appropriate extraction method for X, and justify your answer.

1
First, identify the position of X in the reactivity series: if X does not react with dilute acids and is found native, it is less reactive than copper.
2
No chemical reaction is needed to separate X from impurities.
3
Correct method: Physical purification (e.g. washing, filtering to remove gangue from native metal particles).

Exam tip:

Always explicitly link extraction method justifications to the metal's position in the reactivity series to earn full marks.

2. 2. Extraction of Iron (Core)★★☆☆☆⏱ 15 min

Iron is extracted from its ore haematite ( $F e_{2} O_{3}$ ) in a blast furnace, using four key raw materials: haematite, coke (impure carbon), limestone ( $C a C O_{3}$ ), and hot compressed air.

Hot air is blown into the furnace base, burning coke to form carbon dioxide: $C + O_{2} \to C O_{2}$ . This exothermic reaction heats the furnace to ~1500°C.
Carbon dioxide reacts with hot coke to form carbon monoxide (the reducing agent): $C O_{2} + C \to 2 C O$
Carbon monoxide reduces iron(III) oxide to molten iron, which sinks to the furnace base: $F e_{2} O_{3} + 3 C O \to 2 F e + 3 C O_{2}$
Limestone decomposes to form calcium oxide: $C a C O_{3} \to C a O + C O_{2}$ , which reacts with acidic silica impurities to form molten slag ( $C a S i O_{3}$ ) that floats on iron and is tapped off.

📐 Worked Example

Name the reducing agent in the blast furnace, and write the balanced chemical equation for the reaction that produces pure iron from haematite.

1
The active reducing agent at operating furnace temperature is carbon monoxide, not solid carbon.
2
$Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$
3
Check that all atoms are balanced on both sides of the equation to earn full marks.

3. 3. Extraction of Aluminium (Core)★★★☆☆⏱ 15 min

Aluminium is more reactive than carbon, so it is extracted by electrolysis of molten aluminium oxide obtained from the ore bauxite. Pure aluminium oxide has a very high melting point (~2000°C), so it is mixed with cryolite to lower the melting point to ~900°C, cutting energy costs significantly.

Cathode (negative carbon lining): Al³+ ions gain electrons to form molten aluminium, which sinks to the cell base and is tapped off: $A l^{3 +} + 3 e^{-} \to A l$
Anode (positive carbon electrodes): Oxide ions lose electrons to form oxygen gas: $2 O^{2 -} \to O_{2} + 4 e^{-}$
Carbon anodes are replaced regularly, as hot oxygen reacts with carbon to form carbon dioxide, wearing away the electrodes.

📐 Worked Example

Explain why cryolite is added to aluminium oxide in the electrolytic extraction of aluminium.

1
Pure aluminium oxide has a melting point of ~2000°C, which would require very large amounts of energy to melt, making extraction prohibitively expensive.
2
Cryolite acts as a solvent, dissolving aluminium oxide and lowering the mixture's melting point to ~900°C, reducing energy costs for the process.

4. Common Pitfalls

Wrong move:

Stating carbon is the reducing agent in the blast furnace

Why:

The active reducing agent at operating furnace temperature is carbon monoxide, not solid carbon

Correct move:

Explicitly name carbon monoxide as the reducing agent, linking to its reaction with haematite

Wrong move:

Referring to electrolysis of aqueous aluminium oxide

Why:

Aqueous solutions contain H+ ions that are discharged instead of Al³+ ions, producing hydrogen not aluminium

Correct move:

Specify molten aluminium oxide (mixed with cryolite) is used for electrolysis

Wrong move:

Only stating cryolite lowers melting point, no further justification

Why:

Exam questions require linking the lower melting point to reduced energy costs to earn full marks

Correct move:

Explain cryolite reduces energy costs by lowering the melting point of the aluminium oxide mixture

Wrong move:

Writing anode half equations for oxygen production with electrons on the reactant side

Why:

Oxidation is loss of electrons, so electrons should appear on the product side of the half equation

Correct move:

Write the anode half equation as $2 O^{2 -} \to O_{2} + 4 e^{-}$

Wrong move:

Stating all metals above copper are extracted by electrolysis

Why:

Metals between zinc and copper are extracted by reduction with carbon; only metals above zinc require electrolysis

Correct move:

Always link extraction method to the exact position of the metal in the reactivity series

5. Quick Reference Cheatsheet

Metal	Ore	Extraction Method	Key Reaction
Iron	Haematite ( $F e_{2} O_{3}$ )	Reduction with CO in blast furnace	$F e_{2} O_{3} + 3 C O \to 2 F e + 3 C O_{2}$
Aluminium	Bauxite ( $A l_{2} O_{3}$ )	Electrolysis of molten oxide + cryolite	$2 A l_{2} O_{3} \to 4 A l + 3 O_{2}$
Gold/Silver	Native uncombined	Physical purification	No chemical reaction required

6. Frequently Asked

Why is aluminium extracted using electrolysis not carbon?

Aluminium is more reactive than carbon, so carbon cannot displace it from its ore. Electrolysis of molten aluminium oxide (mixed with cryolite) is required to reduce Al³+ ions to pure aluminium metal.

What is the role of limestone in iron extraction?

Limestone decomposes to form calcium oxide, which reacts with acidic silica impurities in iron ore to form molten slag (calcium silicate). The slag floats on top of molten iron and is tapped off separately for use in road construction.

Going deeper

syllabusCIE IGCSE Chemistry 0620 2026-2028 Specification
study_guideReactivity Series of Metals

What's Next

Now that you have mastered metal extraction for CIE IGCSE Chemistry 0620, move on to related topics that frequently appear alongside extraction questions in exams. Next, revise the uses of metals and alloys, as exam questions often link extraction methods to the properties and real-world applications of the metals produced. Extended tier candidates should practice writing the ionic half-equations for the electrode reactions in aluminium extraction, and the symbol equations for iron extraction, to answer full extended-response questions. You should also review the environmental impacts of industrial extraction, such as the effect of carbon dioxide emissions from the blast furnace, a common synoptic question topic.