Pearson Edexcel International GCSE Chemistry 4CH1: Extraction and uses of metals – Study Guide

This guide teaches sub-topic 2(e) Extraction and uses of metals of the Pearson Edexcel International GCSE Chemistry (4CH1) specification, Issue 3 (September 2024): statements 2.22C to 2.27C. The qualification is untiered. Every statement in 2(e) is printed in bold with a C reference, so the whole sub-topic is Paper 2 only. Chemistry Paper 2 (1 hour 15 minutes, 70 marks) assesses all the content; Paper 1 assesses only the content that is not in bold.

Course links: 4CH1 Chemistry hub, printable checklist and the free all-topics diagnostic. This sub-topic builds directly on the reactivity series, so read the Reactivity and group trends study guide first if the order of the metals is not secure.

What this sub-topic covers

Statement	What you must be able to do	Paper
2.22C	Know that most metals are extracted from ores in the Earth’s crust, and that unreactive metals are often found as the uncombined element	Paper 2 only
2.23C	Explain how the extraction method depends on the metal’s position in the reactivity series, illustrated by carbon extraction for iron and electrolysis for aluminium	Paper 2 only
2.24C	Comment on a metal extraction process, given appropriate information	Paper 2 only
2.25C	Explain the uses of aluminium, copper, iron and steel in terms of their properties (steels limited to low-carbon (mild), high-carbon and stainless)	Paper 2 only
2.26C	Know that an alloy is a mixture of a metal and one or more elements, usually other metals or carbon	Paper 2 only
2.27C	Explain why alloys are harder than pure metals	Paper 2 only

The specification adds a note to 2.24C: detailed knowledge of the processes used to extract a specific metal is not required. You need the principle and the ability to reason from information you are given. Three non-bold statements feed in and can be tested on either paper: 2.17 (the reactivity order), 2.20 (oxidation and reduction) and 1.29 (reacting masses).

Where metals come from (2.22C)

Most metals are found in the Earth’s crust combined with other elements, usually as oxides, sulfides or carbonates. A rock that contains enough of a metal compound to make extracting the metal worthwhile is called an ore. Two examples:

• haematite, which contains iron(III) oxide, Fe₂O₃
• bauxite, which contains aluminium oxide, Al₂O₃

A metal low in the reactivity series does not react readily with oxygen, water or other substances in the ground. So gold is found as the uncombined element, and silver is sometimes found uncombined too. Reactive metals such as sodium and aluminium are never found uncombined.

Extracting a metal from its compound means removing the other element. For an oxide, that means removing oxygen, which is reduction (statement 2.20). In electron terms the metal ions gain electrons to become atoms, which is also reduction.

Choosing an extraction method (2.23C)

Carbon is a non-metal, but you can place it in the reactivity series. It sits between aluminium and zinc.

potassium   \
sodium       |
lithium      |  more reactive than carbon:
calcium      |  extract by ELECTROLYSIS of a molten compound
magnesium    |
aluminium   /
   (carbon)
zinc        \
iron         |  less reactive than carbon:
copper      /   extract by heating the oxide with CARBON
silver      \   very unreactive: gold is found uncombined,
gold        /   silver sometimes

The rule follows from displacement (2.16). Carbon can take oxygen from the oxide of a metal that is less reactive than carbon. It cannot take oxygen from the oxide of a metal that is more reactive than carbon. Those metals hold on to oxygen too strongly, so a more powerful method is needed: electrolysis of the molten compound, which forces electrons onto the metal ions at the cathode. Electrolysis needs large amounts of electricity, so it is only used when carbon will not work.

Illustration 1: iron, by reduction with carbon

Iron is below carbon, so iron(III) oxide in the ore can be reduced by carbon. In the blast furnace, coke (almost pure carbon) burns to form carbon dioxide, which reacts with more hot coke to form carbon monoxide. Carbon monoxide is the main reducing agent:

C + CO₂ → 2CO
Fe₂O₃ + 3CO → 2Fe + 3CO₂

Iron(III) oxide loses oxygen, so it is reduced. Carbon monoxide gains oxygen, so it is oxidised and is the reducing agent. You do not need further detail of the blast furnace.

Illustration 2: aluminium, by electrolysis

Aluminium is above carbon, so carbon cannot reduce aluminium oxide. Aluminium oxide is electrolysed instead. It has a melting point above 2000 °C, so it is dissolved in molten cryolite. The solution conducts at under 1000 °C, which saves energy. The electrodes are graphite (carbon).

cathode (−):  Al³⁺ + 3e⁻ → Al        reduction (gain of electrons)
anode (+):    2O²⁻ → O₂ + 4e⁻        oxidation (loss of electrons)

At the high temperature, the oxygen reacts with the carbon anodes to form carbon dioxide. The anodes burn away and must be replaced regularly. The large electricity demand is the main cost.

Worked example 1: choosing a method

A metal M lies between magnesium and aluminium in the reactivity series. A second metal Q lies between zinc and iron. Explain how each is most likely to be extracted from its oxide.

M: above aluminium, so above carbon.
   Carbon cannot remove oxygen from M's oxide.
   -> electrolysis of a molten compound of M.
Q: below zinc, so below carbon.
   Carbon can remove oxygen from Q's oxide.
   -> heat the oxide with carbon (cheaper than electrolysis).

Each answer needs the method and the reason linked to carbon’s position.

Worked example 2: reacting masses in extraction

Calculate the maximum mass of aluminium that can be extracted from 51.0 tonnes of aluminium oxide. (Ar: Al = 27, O = 16)

Mr(Al2O3) = 2(27) + 3(16) = 102
102 t of Al2O3 contains 2 x 27 = 54 t of Al
mass of Al = 51.0 x 54/102 = 27.0 tonnes

The same method gives the percentage of iron in Fe₂O₃: 112/160 × 100 = 70.0%.

Commenting on an extraction process (2.24C)

You are given information about a process you have not studied. Use the information, and test it against these points:

Point to check	What to say
Reactivity	Is the reducing agent (carbon, or a metal) more reactive than the metal being extracted?
Energy	Is a high temperature or electricity needed? Both cost money.
Raw materials	Is a reactant itself expensive to make?
Conditions	Why is air kept out, or a substance added?
Environment	Is CO₂ or another harmful gas made? Is land damaged by mining?
Recycling	Could recycling save ore and energy?

Worked example 3: titanium

You are given this information:

Titanium is extracted by heating titanium(IV) chloride with molten magnesium at about 800–850 °C in an argon atmosphere. The magnesium chloride formed is converted back into magnesium by electrolysis. TiCl₄ + 2Mg → Ti + 2MgCl₂

Comment on this process.

1. Magnesium can displace titanium, so magnesium must be more reactive than titanium.
2. Magnesium is itself made by electrolysis, so it is expensive to produce. The high temperature also needs a lot of energy. Both make titanium expensive.
3. Argon is unreactive. It keeps oxygen out, so the hot metals do not react with air.
4. Turning magnesium chloride back into magnesium reuses the magnesium, which cuts the amount of new raw material needed.
5. The information does not say why carbon is not used, so do not invent a reason. Stick to what the information supports.

A short calculation can be attached. To make 4.80 kg of titanium (Ar Ti = 48, Mg = 24):

moles of Ti = 4800 g / 48 = 100 mol
moles of Mg = 2 x 100 = 200 mol
mass of Mg  = 200 x 24 = 4800 g = 4.80 kg

Recycling

Recycling scrap aluminium needs only about 5% of the energy used to make new aluminium from its ore. It also saves ore and reduces mining waste.

Uses of aluminium, copper, iron and steel (2.25C)

“Explain the use” means give the property and link it to why it suits the use.

Metal	Property	Use it explains
Aluminium	Low density; strong when alloyed	Aircraft bodies
Aluminium	Low density and good electrical conductor	Overhead power cables
Aluminium	Resists corrosion: a thin layer of aluminium oxide protects the surface	Drinks cans, window frames, food foil
Copper	Very good electrical conductor; ductile (can be drawn into wires)	Electrical wiring
Copper	Does not react with water; can be bent into shape	Water pipes
Copper	Good conductor of heat	Bases of saucepans

Iron and steel

Pure iron is quite soft, and iron straight from the blast furnace contains about 4% carbon, which makes it brittle. Most iron is therefore turned into steel, an alloy of iron with carbon and sometimes other elements. Changing the amount of carbon, or adding other metals, changes the properties.

Steel	Composition	Properties	Uses
Low-carbon (mild) steel	Up to about 0.3% carbon	Strong, malleable, easily shaped, cheap; rusts unless protected	Car body panels, building frames, pipes, food cans
High-carbon steel	About 0.6–1.0% carbon	Very hard and strong, but brittle	Cutting tools, springs
Stainless steel	Iron with at least 10.5% chromium, often with nickel	Resists corrosion; hard	Cutlery, cookware, surgical instruments

Mild steel must be protected from rusting (2.19). Stainless steel resists corrosion because chromium forms a protective oxide layer.

Alloys (2.26C and 2.27C)

An alloy is a mixture of a metal and one or more other elements, usually other metals or carbon. It is a mixture, not a compound: the elements are not chemically bonded in fixed proportions. Examples are steel (iron and carbon), stainless steel (iron, chromium and often nickel) and brass (copper and zinc).

Why alloys are harder

In a pure metal all the atoms are the same size and are arranged in regular layers. When a force is applied, the layers can slide over each other. This is why pure metals are malleable and fairly soft (see metallic bonding, 1.52C–1.54C).

pure metal                    alloy
O O O O O O                   O O O O O O
O O O O O O    force ->       O O @ O O O    @ = larger atom
O O O O O O                   O O O O O O    layers distorted,
(layers slide easily)         (sliding is harder)

In an alloy, atoms of a different size disrupt the regular layers. The layers are distorted, so it is harder for them to slide over each other. The alloy is therefore harder than the pure metal.

Worked example 4: brass

Explain why brass is harder than pure copper. [3]

1. Brass contains zinc atoms, which are a different size
   from copper atoms.
2. These atoms distort the regular layers of copper atoms.
3. So the layers cannot slide over each other as easily.

“Brass is stronger because it is a mixture” would score nothing. Credit goes to the different-sized atoms and their effect on the sliding of layers.

Common errors

• Placing carbon in the wrong position. It goes between aluminium and zinc, so aluminium cannot be extracted with carbon but zinc can.
• Saying electrolysis is used “because the metal is reactive” without comparing it with carbon.
• Saying aluminium oxide is melted on its own. It is dissolved in molten cryolite to lower the operating temperature.
• Saying the anodes are replaced because they “wear out”. The oxygen formed reacts with the carbon anodes to make carbon dioxide.
• Writing that atoms in an alloy “stop the layers moving”. They make sliding harder; they do not stop it completely.
• Giving “aluminium is light” for aircraft. Use the property name: “low density”.
• Inventing facts in a 2.24C answer.

Next steps

Condense this into the extraction and uses of metals revision notes, then test yourself with the extraction and uses of metals practice questions. For related content, see the electrolysis study guide, the bonding study guide for metallic lattices, and the topic-level reactivity practice.

Official syllabus

Pearson Edexcel International GCSE in Chemistry (4CH1), Specification, Issue 3, September 2024, published by Pearson Education Limited. Topic 2: Inorganic chemistry, sub-topic (e) Extraction and uses of metals, statements 2.22C–2.27C.