Uses of MetalsCambridge IGCSE Chemistry: Revision notes
Section 1
Why do we select specific metals for specific applications?
Metals are chosen for particular uses based on their physical properties. Different metals have different combinations of properties that make them suitable for different jobs. Understanding the link between a metal's properties and its application is essential for exam success. The main physical properties that determine metal use include:
- Density – how heavy the metal is for a given volume
- Electrical conductivity – how well the metal conducts electricity
- Corrosion resistance – how well the metal resists damage from environmental exposure
- Ductility – how easily the metal can be drawn into wires without breaking
Always link the metal's property directly to why it is used in that application. Examiners want to see you explain the connection, not just list properties.
Section 2
How is aluminium used in aircraft and why?
Aluminium is used in aircraft because it has a very low density. This means aluminium is very light for its strength. Low density is critical in aircraft design because:
- Lighter aircraft require less fuel to fly, reducing operating costs
- Less weight means better performance and faster acceleration
- Planes can carry more cargo or passengers without exceeding weight limits
Aluminium's low density makes it far more suitable for aircraft than heavier metals like steel or iron, which would make planes too heavy to fly efficiently. The combination of low density with reasonable strength makes aluminium the ideal choice for aircraft frames, wings, and fuselage.
If asked why aluminium rather than steel for aircraft: Steel is stronger, but it is much denser (heavier). The extra weight would require more fuel and reduce flight efficiency, so aluminium's low density outweighs steel's superior strength in this application.
Students often say 'aluminium is strong' as the main reason for aircraft use. The key reason is its LOW DENSITY – strength is secondary. Always prioritise density in your answer.
Section 3
Why is aluminium chosen for overhead electrical cables?
Aluminium is used in overhead power cables because it has both low density and good electrical conductivity.
Low density advantage:
- Cables must span long distances between electricity pylons
- Light cables reduce the structural stress on the supporting pylons and cables themselves
- Reduces the amount of material needed, lowering cost
Good electrical conductivity advantage:
- Electricity must flow efficiently through the cable with minimal energy loss as heat
- Good conductivity ensures effective power transmission over long distances
- Reduces wasted energy and heat generation
Copper would conduct electricity better, but it is much denser and more expensive. Aluminium provides the optimal balance of both properties needed for this application.
Think of overhead cables like a tightrope: you want the rope to be light (so it doesn't sag under its own weight) and conductive (so electricity can flow freely). Aluminium is the best 'all-rounder' for both needs.
When discussing overhead cables, mention BOTH properties – low density AND good electrical conductivity. Examiners look for understanding that both properties are needed together.
Section 4
What makes aluminium suitable for food containers?
Aluminium is used in food containers and packaging because it is resistant to corrosion. This property is crucial for food storage because:
- Aluminium naturally forms a thin, protective oxide layer on its surface that prevents further oxidation and corrosion
- This oxide layer means the metal does not rust or corrode when exposed to air, moisture, or acidic/alkaline foods
- The container maintains its integrity and does not leak or degrade, keeping food fresh and safe
- No toxic rust particles can contaminate the food
- The containers are lightweight and easy to transport and recycle
Unlike steel or iron, which rust and weaken when exposed to moisture, aluminium remains chemically stable and durable. This makes it ideal for protecting food and extending shelf life.
Iron food cans rust quickly when exposed to moisture and acidic foods, creating iron oxide (rust) that flakes into the food. Aluminium cans do not rust because the protective oxide layer keeps water and acids away from the underlying metal.
Do not confuse 'corrosion resistant' with 'cannot corrode at all'. Aluminium is highly resistant because of its oxide layer, but the focus should be on how this layer protects it in food storage.
Section 5
Why is copper ideal for electrical wiring?
Copper is used in electrical wiring because it has excellent electrical conductivity and is highly ductile.
Electrical conductivity advantage:
- Copper conducts electricity extremely well, with minimal resistance
- Allows current to flow efficiently from the power source to appliances and devices
- Reduces energy loss as heat, making electrical systems safe and efficient
- Only silver conducts better, but silver is far too expensive for widespread use
Ductility advantage:
- Copper can be drawn out into long, thin wires without breaking
- This property is essential because wiring must be flexible and bendable to fit through walls, around corners, and into tight spaces
- Ductile copper wires can be easily installed, repaired, and shaped without cracking or snapping
- The wires can withstand physical stress during installation and use
Copper's combination of properties makes it the standard choice for household and industrial electrical wiring worldwide.
If asked to compare copper and aluminium for wiring: Copper conducts electricity better (lower resistance), but aluminium is lighter. However, copper's superior conductivity outweighs this because energy loss as heat is more important to control than weight in most electrical wiring applications.
For copper wiring, always mention BOTH conductivity AND ductility. Conductivity allows current flow; ductility allows the wire to be shaped and installed. Both are essential.
Must Know
- Aluminium in aircraft: Low density makes it light, reducing weight and fuel consumption – strength is secondary
- Aluminium in overhead cables: Low density reduces stress on pylons; good electrical conductivity allows efficient power transmission
- Aluminium in food containers: Corrosion resistance (protective oxide layer) prevents rust and keeps food safe and uncontaminated
- Copper in electrical wiring: Excellent electrical conductivity allows efficient current flow with minimal energy loss; ductility allows wires to be drawn and shaped without breaking
- Always link property to application: Examiners mark you down if you list properties without explaining WHY that property makes the metal suitable for that use
- Multiple properties matter: Some applications (overhead cables, copper wiring) require multiple properties working together – identify all relevant properties
That's the notes covered.
Carry on to the next subtopic.