The shape of the lesson
By the end of the lesson, learners can
- Aluminium and copper: For each use, give the property that makes the metal suitable.
- Choosing a material: Exam questions often give a table of data and ask you to pick a metal for a job.
- Aircraft: aluminium, low density, strong alloys.
- Overhead cables: aluminium, low density, conducts.
- Food containers: aluminium, resists corrosion.
- Wiring: copper, conducts, ductile.
One picture every idea returns to
Choose a metal by matching its properties to the job. Aluminium is used in aircraft (low density, and strong as an alloy), overhead power cables (low density and a good electrical conductor) and food containers (resistant to corrosion). Copper is used in electrical wiring because it is a good conductor of electricity and is ductile.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, The right metal for the job.. Every use of a metal can be traced to a property. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Aluminium and copper | For each use, give the property that makes the metal suitable. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Choosing a material | Exam questions often give a table of data and ask you to pick a metal for a job. | Quiz-Quiz-Trade |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 12 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Choosing a material, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Quiz-Quiz-Trade
Each student holds a card with a question on the front and the answer on the back. They pair up, quiz each other, coach if needed, trade cards and find a new partner. Three rounds covers the whole set.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Aluminium resists corrosion not because it is unreactive (it is high in the reactivity series) but because of a thin, tough layer of aluminium oxide that seals the surface. | Say "resists corrosion", not "is unreactive". |
Uses of metals: worksheet
6 questions, 12 marks. Written in the style of the papers; no past paper question is reproduced.
Give two properties of aluminium that make it suitable for making aircraft.
Give two properties of copper that make it suitable for electrical wiring.
Explain why aluminium food containers do not corrode, even though aluminium is a reactive metal.
Copper is a better conductor than aluminium, but aluminium is used for overhead cables. Use the data (density: aluminium 2.7 g/cm3, copper 8.9 g/cm3) to explain why.
Suggest why iron is not used for overhead power cables.
State one use of aluminium other than aircraft and power cables.
Answer key and marking notes
- Low density.
- Strong (as an alloy) and resistant to corrosion.
- Good conductor of electricity.
- Ductile (can be drawn into wires).
- Aluminium reacts with oxygen to form a thin layer of aluminium oxide on its surface.
- This layer is unreactive and stops air and water reaching the metal underneath.
- Aluminium is much less dense than copper (about one third).
- So an aluminium cable is much lighter, and fewer, cheaper pylons are needed.
- Aluminium is still a good enough conductor for the job.
- Iron has a high density, so the cables would be very heavy.
- Iron rusts, and it is a poorer conductor than aluminium.
Food containers, drinks cans, cooking foil or window frames.
7 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Many saucepans have a copper base. Which property of copper is the main reason for this use?
- Ait is a good conductor of heat
- Bit has a low density
- Cit is magnetic
- Dit has a low melting point
Copper is often used for household water pipes. Which property makes it suitable?
- Ait does not corrode easily in water
- Bit is a good conductor of electricity
- Cit reacts with water to form a protective hydroxide layer
- Dit has a very low density
The table shows data for four metals.
| Metal | Density / g/cm3 | Corrodes in damp air? |
|---|---|---|
| aluminium | 2.7 | no |
| iron | 7.9 | yes, rusts |
| copper | 8.9 | very slowly |
| lead | 11.3 | very slowly |
- Aaluminium
- Biron
- Ccopper
- Dlead
A student writes: "Aluminium is used for food containers because it is an unreactive metal." What is wrong with this statement?
- Aaluminium is a reactive metal; it resists corrosion because of a thin layer of aluminium oxide
- Bnothing is wrong: aluminium is below hydrogen in the reactivity series
- Caluminium is used because it reacts with food acids to preserve the food
- Daluminium is not used for food containers because it corrodes quickly
Gold is an excellent conductor of electricity and is very ductile. Why is it not used for the wiring in houses?
- Ait is far too expensive for such large amounts
- Bit is a poor conductor of electricity
- Cit corrodes quickly in air
- Dit cannot be drawn into wires
A section of overhead cable contains 500 cm3 of metal. The density of aluminium is 2.7 g/cm3 and that of copper is 8.9 g/cm3. How much lighter is the aluminium section than an identical copper section?
- A3100 g
- B6.2 g
- C1350 g
- D4450 g
Which use of aluminium depends mainly on its resistance to corrosion rather than on its low density?
- Acontainers for food
- Bthe bodies of aircraft
- Coverhead power cables
- Dlightweight bicycle frames
Quiz key
The base must pass energy quickly and evenly from the hob to the food, so a good thermal conductor such as copper is ideal. Copper actually has a high density (8.9 g/cm3), so low density is not the reason. Copper is not magnetic, and a low melting point would be a disadvantage for a pan; copper melts at over 1000 °C.
Copper is below hydrogen in the reactivity series and does not react with water, so pipes last a long time without corroding (copper is also easy to bend into shape). Electrical conductivity is true of copper but has nothing to do with carrying water. Copper does not react with water, so no hydroxide layer forms. Copper is a dense metal, not a low-density one.
Aluminium has by far the lowest density, so the frames are light, and its oxide layer stops it corroding, so no paint is needed. Iron rusts in damp air and would need painting. Copper and lead resist corrosion, but they are about three to four times as dense as aluminium, so the frames would be very heavy.
Aluminium is high in the reactivity series, above zinc and iron, so it is not unreactive. It resists corrosion because it is quickly covered by a thin, tough layer of aluminium oxide that seals the surface. Aluminium is above hydrogen, not below it. A container that reacted with food would contaminate it, and aluminium does not corrode quickly, which is why it is widely used for foil, trays and cans.
Gold has the right properties, but a house needs many metres of wire and gold is rare and very costly, so copper, which is nearly as good a conductor and much cheaper, is used instead. The stem states that gold conducts well and is ductile, so the options claiming it is a poor conductor or cannot be drawn into wires contradict the data. Gold is at the bottom of the reactivity series and does not corrode.
Mass of aluminium = 2.7 × 500 = 1350 g. Mass of copper = 8.9 × 500 = 4450 g. The difference is 4450 − 1350 = 3100 g, so the aluminium section is 3.1 kg lighter. The value 6.2 g comes from subtracting the densities without multiplying by the volume. 1350 g and 4450 g are the masses of the individual sections, not the difference between them.
A food container must not corrode or contaminate the food, and the weight of a small tray or can hardly matters, so corrosion resistance is the key property. Aircraft bodies and bicycle frames are chosen above all for being light (and strong as alloys). Overhead cables rely on low density, so the pylons carry less weight, together with good electrical conductivity.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.