To choose a material, list each requirement, check it against the material’s properties, and explain why the next-best option fails. Naming the material is only the start, and the reasoning is where most marks come from.
This is the last lesson in SPM Chemistry manufactured materials. It builds on relating polymer and composite properties to uses.
What is the method for choosing a material?
Work in four short steps. They turn a hunch into written reasoning.
- Underline every requirement in the question, such as light, strong, rust-proof or heat resistant.
- Write a one-word property for each requirement.
- Check each candidate material against each property.
- Choose the one that meets all of them and say why the other fails one.
Worked example: a fishing boat hull
Question. A boat maker needs a hull that is light, strong, rust-free in seawater and easy to mould. Choose steel, fibre glass or ceramic and justify it for 4 marks.
Score each option against the four requirements.
| Requirement | Steel | Fibre glass | Ceramic |
|---|---|---|---|
| Light | No, dense | Yes | No, heavy |
| Strong | Yes | Yes | Hard but brittle |
| No rust in seawater | No, iron rusts | Yes | Yes |
| Easy to mould | Hard to shape | Yes, set in a mould | No, needs firing |
Answer.
- Fibre glass is the best choice because it meets all four requirements.
- It is a composite: glass fibres give strength and plastic gives shape, so it is light yet strong.
- It does not rust, because the plastic and glass do not react with seawater.
- Steel is strong but dense and rusts, and ceramic is brittle and would crack when the hull hits a wave.
The table takes one minute to draw in the margin. The last sentence matters most, because it shows you compared the options.
Where do marks slip?
The usual slip is to name a property but not link it to the requirement. “Fibre glass is strong” is weaker than “fibre glass is strong, so the hull does not break when a wave hits it”.
A second slip is ignoring a requirement. If the question lists four and your answer covers two, the other two marks are lost. Record which requirement you skip in your mistake log and watch for the pattern.
Check yourself
A school needs a material for the handles of laboratory tongs used near a Bunsen flame. The handle must not conduct heat, must not soften when hot and must be light. Choose between copper, a thermoplastic and a thermosetting polymer, and justify it.
Answer
Choose the thermosetting polymer. It is a poor conductor of heat, so the handle does not burn the user’s hand. Its cross-linked chains mean it does not soften near the flame, and its density is low, so the handle is light.
Copper conducts heat well, so the handle becomes hot. A thermoplastic softens when heated, so it would lose its shape.
What to study next
Try the full set in the manufactured materials practice page, which mixes alloys, glass, ceramics, polymers and composites. Review the wider SPM Chemistry exam guide for how structured answers are marked.
If you want a teacher to give you fresh scenarios and mark your justification, see online one-to-one Chemistry tuition.