The big idea: A chemical property describes an aspect of a material that leads to it reacting with another substance.
The material is altered by the encounter — which is exactly what separates these from physical properties.
Each property drawn as the material meeting something else and changing.
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Corrosion resistance
How well it survives reacting with oxygen, water and salt. Iron rusts and keeps rusting; aluminium forms a thin oxide layer that then protects it; stainless steel's chromium forms a self-repairing film. It decides whether a product survives a bathroom, a coast or a gritted road.
Reactivity — food safe
Whether it reacts with what it touches. A food-safe material does not react with food, leach into it, or taint flavour. Untreated copper reacts with acidic food; some polymers release compounds when heated. The requirement is chemical inertness against what it will actually hold.
Hygroscopy
Whether it absorbs moisture from the air and changes as it does. Timber swells and warps, nylon softens, cardboard loses strength. It is why a wooden door sticks in a wet season and why some polymers must be dried before moulding.
Flammability
How readily it ignites and keeps burning. Regulated for furniture, building materials, children's nightwear and vehicle interiors — and the answer is usually a different grade of material rather than a coating.
Two uses the papers ask about
Absorbency can be wanted
Sports kit and towels use fibres that absorb moisture, taking sweat away from the skin. Hygroscopy is a problem in a timber door and a benefit in a towel.
Glass is unreactive
Glass does not react with water, food or acids, so it is used for food jars, drinking glasses and fish tanks: nothing leaches out.
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Chemical properties are about the environment the product lives in. They tend to eliminate candidates rather than rank them, because a material that corrodes in the product's actual setting is simply out.
| Product | The environment | Chemical property that decides |
|---|---|---|
| Shower fitting | Constant warm damp | Corrosion resistance, not hygroscopic |
| Lunch box | Acidic and oily food | Food-safe reactivity |
| Outdoor bench | Rain, frost, sun | Corrosion resistance and hygroscopy |
| Sofa foam | A living room | Flammability, to a regulated grade |
| Garden tool handle | A damp shed | Hygroscopy, or it swells and splits |
The trap: Naming a chemical property without naming what it reacts with. "Corrosion resistant" is half an answer; "corrosion resistant, because it is splashed with salty water daily" is the whole one.
How this is tested — explaining the chemical properties and applying them to an environment. It comes up two ways:
Paper 1 — multiple choice
- Identify the chemical property a described failure shows.
- Pick the property that suits a stated environment.
Paper 2 — analysing a product
- Explain the chemical properties needed for a product's setting.
- Explain why a material failed in a described environment.
The trap: Confusing chemical with physical. Melting is physical — the material is unchanged when it resolidifies. Burning is chemical — it becomes something else.
A wooden garden bench is left outdoors all year and begins to split after two winters. Explain the chemical properties involved and how a redesign could address them.
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