Lesson focus: Why can the same family of materials make a flexible bag and a rigidStiff, so it does not bend easily. helmet?
Connect the propertyA feature of a material you can observe or measure, such as how hard or bendy it is. of plasticA material made from long-chain molecules called polymers, used for bottles, bags and toys. to their uses and describe a polymerA very long molecule made by joining lots of small molecules together in a chain..
Build on earlier learning
Compounds and molecules: modelsUse particle models to connect molecular structure with material properties.
Practical
Testing plastic properties
- Test each plastic strip for flexibility, strength and how it responds to warm water.
- Use the same strip size and test method for each.
Record: A table of properties and a recommended use for each plastic.
You will be successful when you can…
- Define polymer and plastic.
- Distinguish a material from a molecule.
- Link properties to uses.
- Use a chain model without overclaiming.
Words that carry the science
- polymer
- A large molecule made from many repeating smaller units.
- plastic
- A material based on polymers, usually combined with additives.
- property
- A measurable or observable feature of a material.
- additive
- A substance mixed into a material to alter its properties.
- rigid
- Resistant to bending or changing shape.
Explain a plastic property from evidence, not from its name
01Polymer is not another word for plastic
A polymer is a type of large molecule. A plasticA material made from long-chain molecules called polymers, used for bottles, bags and toys. is a material containing polymerA very long molecule made by joining lots of small molecules together in a chain. and often colourants, fillers, plasticisers or other additiveSomething added to a material to change its properties, such as colour added to plastic..
02Structure helps explain properties
Chain identity, length, branching, organisation and forces or links between chains affect how easily chains move. Additives and processing also matter.
03Judge fitness for purpose
A raincoat needs low mass, flexibility and water resistance. A helmet shell needs rigidity and impact resistance. No single propertyA feature of a material you can observe or measure, such as how hard or bendy it is. makes a material suitable for every use. For example, a raincoat plastic is waterproofDoes not let water soak in or pass through, like a raincoat., so rain cannot get through and you stay dry. It is lightweightHas a small mass for its size, so it is easy to carry or lift., so the coat is easy to wear and carry. It is flexibleBends easily without breaking, like a rubber hose., so it bends when you move.
Choose a material for a raincoat
Candidate X is waterproof, flexible and low-density. Candidate Y is waterproof, rigidStiff, so it does not bend easily. and twice the mass.
- Identify the required service: protect a moving wearer from rain.
- Both candidates meet the water-resistance requirement.
- X bends as the wearer moves and contributes less mass.
- Choose X while noting that durability would also need testing.
How to make the reasoning visible: A justified choice links measured properties to the intended use.
Property–use evidence map
Compare materials by the service they must provide.
| Object | Needed property | Evidence or test | Why it matters |
|---|---|---|---|
| Raincoat | Flexible | Repeated bend test | Allows movement |
| Drinks bottle | Low permeability | Measure leakage or mass change | Contains liquid |
| Helmet shell | Rigid and impact resistant | Controlled impact test | Keeps protective shape |
| Cable coating | Electrical insulator | Conductivity test | Reduces current through user |
Why is “made of plastic” not a complete property description?
Why might a plasticiser make a polymer material more flexible?
Use the table. Why is plastic used to coat electrical cables?
Check your understanding
Answer from memory, then check against the suggested answer.
What is a polymer?
What is an additive?
What does rigid mean?
Give two properties that make plastics useful.
What does flexible mean?
A tray and a carrier bag are both plastics. Why can one be rigid and the other flexible?
Why does a chain model support an explanation but not prove the exact structure of a sample?
Why would a plastic used for a raincoat not be suitable for a bike helmet?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A raincoat is made from a plastic that is waterproof, lightweight and flexible. Answer the parts to explain why it is a good choice.
What does waterproof stop?
(1)So how does this help the person wearing it?
(1)Why is lightweight useful for a coat?
(1)Why is flexible useful for a coat?
(1)Total for this question: 4 marks
Command word: For each property, say why it is useful, using “so” or “because”.