Pearson Edexcel International GCSE Chemistry 4CH1: Extraction and uses of metals – Revision Notes

Condensed recall for the final weeks. For full explanations and worked examples, use the extraction and uses of metals study guide.

These notes cover 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–2.27C. The qualification is untiered. All six statements carry a C reference, so the whole sub-topic is Paper 2 only (1 hour 15 minutes, 70 marks). Course links: 4CH1 Chemistry hub, printable checklist, the free all-topics diagnostic and the practice questions for this sub-topic. The reactivity order itself is in the reactivity revision notes.

2.22C Ores and native metals

• Ore: rock containing enough of a metal compound to make extracting the metal worthwhile.
• Most metals are extracted from ores in the Earth’s crust, where they are combined, often as oxides.
• Iron ore (haematite) contains Fe₂O₃. Aluminium ore (bauxite) contains Al₂O₃.
• Unreactive metals are often found as the uncombined element: gold, and sometimes silver.
• Extracting a metal from its oxide = removing oxygen = reduction. Metal ions gain electrons = also reduction.

2.23C Method depends on reactivity

K  Na  Li  Ca  Mg  Al   ->  electrolysis of molten compound
        (C)              ->  carbon sits here
Zn  Fe  Cu              ->  heat oxide with carbon
Ag  Au                  ->  often found uncombined
                            (gold; silver sometimes)

Method in steps: choosing the method

1. Find the metal in the reactivity series.
2. Compare it with carbon (between Al and Zn).
3. Below carbon → heat the oxide with carbon. Carbon removes the oxygen.
4. Above carbon → electrolysis of a molten compound. Carbon cannot remove the oxygen.
5. Give the reason, not just the method.

Electrolysis uses a lot of electricity, so it costs more. It is used only when carbon will not work.

Iron: reduction with carbon

Step	Equation
Carbon monoxide formed from coke	C + CO₂ → 2CO
Iron(III) oxide reduced	Fe₂O₃ + 3CO → 2Fe + 3CO₂

• Iron(III) oxide is reduced (loses oxygen). Carbon monoxide is oxidised and is the reducing agent.
• Detailed knowledge of the blast furnace is not required.

Aluminium: electrolysis

Feature	Recall
Electrolyte	Aluminium oxide dissolved in molten cryolite
Why cryolite	Al₂O₃ melts above 2000 °C; the solution works below 1000 °C, saving energy
Electrodes	Graphite (carbon)
Cathode (−)	Al³⁺ + 3e⁻ → Al (reduction)
Anode (+)	2O²⁻ → O₂ + 4e⁻ (oxidation)
Anodes replaced	Oxygen reacts with the hot carbon anodes to form CO₂, so they burn away
Main cost	Electricity

2.24C Commenting on a process

You will be given the information. Detailed knowledge of any specific process is not required.

Method in steps: commenting on a process

1. Reactivity: is the reducing agent more reactive than the metal?
2. Energy: high temperature or electricity → expensive.
3. Raw materials: is the reducing agent itself costly to make?
4. Conditions: why is air kept out (argon), or a substance added?
5. Environment: CO₂ released; mining damages land.
6. Recycling: saves ore and energy. Recycled aluminium needs about 5% of the energy of new aluminium.
7. Use only what the information supports.

2.25C Uses linked to properties

Metal	Property	Use
Aluminium	Low density, strong as an alloy	Aircraft
Aluminium	Low density, conducts electricity	Overhead power cables
Aluminium	Resists corrosion (protective oxide layer)	Cans, window frames, foil
Copper	Very good electrical conductor, ductile	Wiring
Copper	Does not react with water	Water pipes
Copper	Good thermal conductor	Saucepan bases
Iron	Pure iron is soft; blast-furnace iron (about 4% C) is brittle	Mostly turned into steel

The three steels

Steel	Carbon / other elements	Key property	Use
Low-carbon (mild)	Up to about 0.3% C	Strong, malleable, cheap; rusts	Car bodies, building frames, food cans
High-carbon	About 0.6–1.0% C	Very hard and strong, brittle	Cutting tools, springs
Stainless	At least 10.5% chromium, often nickel	Resists corrosion	Cutlery, cookware, surgical instruments

Memory hook: more carbon → harder but more brittle.

2.26C and 2.27C Alloys

• Alloy: a mixture of a metal and one or more elements, usually other metals or carbon.
• Examples: steel (Fe + C), brass (Cu + Zn), stainless steel (Fe + Cr, often Ni).

Three-point explanation: why alloys are harder

1. Pure metal: atoms all the same size in regular layers, which slide easily.
2. Alloy: atoms of a different size distort the layers.
3. So the layers slide over each other less easily → harder.

Must-know distinctions

Don’t confuse	With
Iron(III) oxide is reduced	Carbon monoxide is oxidised (the reducing agent)
Carbon reduction (metals below C)	Electrolysis (metals above C)
Alloy = mixture	Compound = elements chemically bonded in fixed ratio
“Low density” (property)	“Light” (not the property term)
Mild steel: malleable, rusts	Stainless steel: resists corrosion
High-carbon steel: hard, brittle	Mild steel: softer, easily shaped
Al₂O₃ dissolved in cryolite	Al₂O₃ melted on its own (wrong)

Small worked reminders

Percentage of metal in an ore compound. Copper(I) sulfide, Cu₂S (Ar: Cu = 63.5, S = 32):

Mr = 2(63.5) + 32 = 159
% Cu = 127/159 x 100 = 79.9%

Mass of metal from a mass of oxide. Use the mass ratio in the formula: Mr(Fe₂O₃) = 160 and it contains 2 × 56 = 112 of iron, so 160 t of Fe₂O₃ gives at most 112 t of Fe. Scale this ratio to the mass given.

Links to the rest of the course

Other statement	How it connects here
2.16 displacement	Carbon reducing a metal oxide works like a more reactive metal displacing a less reactive one from its oxide
2.19 rust prevention	Mild steel rusts, so it needs paint, oil or galvanising
2.20 redox terms	Oxide reduced, reducing agent oxidised; metal ions gain electrons
1.29 reacting masses	Mass of metal from a given mass of ore or oxide
1.52C–1.54C metallic bonding	Regular layers of positive ions explain malleability, and why alloys are harder
1.59C half-equations	Electrode equations in aluminium extraction

What the command words want

• State / Name: one fact, no reason (e.g. “carbon monoxide”).
• Explain: a fact plus a linked reason, often with “because” or “so”. For a use, that is property + why it suits the use.
• Comment on: points for and against drawn from the information, with reasons. Cover more than one area (energy, cost, environment) when the mark total allows.
• Calculate: show the Mr, the ratio and the final answer with units; round sensibly (3 significant figures is usually safe).

Quick self-test

1. Define an ore.
2. Why is gold found as the uncombined element?
3. Where does carbon go in the reactivity series?
4. Zinc oxide is heated with carbon. Name the products and state which substance is reduced.
5. Explain why aluminium is extracted by electrolysis, not by heating its oxide with carbon. Why is this method expensive?
6. Why is aluminium oxide dissolved in cryolite?
7. Write the half-equation at the cathode in aluminium extraction.
8. Calculate the mass of iron that could be obtained from 400 tonnes of Fe₂O₃. (Ar: Fe = 56, O = 16)
9. Calculate the percentage by mass of zinc in zinc oxide, ZnO. (Ar: Zn = 65, O = 16)
10. Making new aluminium uses about 15 kWh per kg. Recycling uses about 5% of this. Calculate the energy to make 1 kg of recycled aluminium.
11. Which steel would you choose for a chisel blade, and why?
12. Why is stainless steel used for cutlery?

Answers

1. A rock containing enough of a metal compound to make extracting the metal worthwhile.
2. Gold is very unreactive, so it does not react with substances in the ground.
3. Between aluminium and zinc.
4. Zinc and carbon monoxide (ZnO + C → Zn + CO). Zinc oxide is reduced.
5. Aluminium is more reactive than carbon, so carbon cannot remove oxygen from aluminium oxide. Electrolysis needs a large amount of electricity.
6. Aluminium oxide melts above 2000 °C; the solution in cryolite can be electrolysed at a lower temperature, saving energy.
7. Al³⁺ + 3e⁻ → Al
8. 400 × 112/160 = 280 tonnes.
9. Mr = 81; 65/81 × 100 = 80.2%.
10. 0.05 × 15 = 0.75 kWh.
11. High-carbon steel: it is very hard, so it keeps a cutting edge.
12. It resists corrosion, so it does not rust when washed or in contact with food.

Where marks are usually lost

• Saying electrolysis is used “because aluminium is reactive” with no comparison with carbon.
• Putting carbon above aluminium, or below zinc.
• Writing “iron is reduced” instead of “iron(III) oxide is reduced”.
• Missing the reason the anodes are replaced: oxygen reacts with the carbon anodes to form carbon dioxide.
• Writing “aluminium oxide is melted” without cryolite, or saying cryolite is a catalyst.
• Giving a use without the property, or a property without linking it to the use.
• Writing “aluminium is light” instead of “low density”.
• Saying alloy atoms “stop the layers sliding” rather than making sliding harder; leaving out “different-sized atoms”.
• Calling an alloy a compound.
• Adding outside facts to a “comment on this process” answer instead of using the information given.

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.