Cambridge Primary Checkpoint 0846 · Topic 6 of 10

Materials, states of matter and changes

Properties of materials, solids, liquids and gases, changes of state, dissolving and separating mixtures, and reversible and irreversible changes.

📌 Key points

Materials are chosen for their properties: metals are strong and conduct heat and electricity, glass is transparent, and rubber is flexible and waterproof.
Conductors let heat or electricity pass through easily (metals). Insulators do not (plastic, wood, wool).
Only some metals are magnetic, such as iron, steel and nickel. Aluminium, copper and gold are not magnetic.
Solids keep their shape. Liquids flow and take the shape of their container. Gases spread out to fill any space.
In a solid the particles are packed tightly and vibrate in place. In a liquid they are close but move around. In a gas they are far apart and move quickly.
Melting: solid → liquid. Freezing: liquid → solid. Evaporating: liquid → gas. Condensing: gas → liquid. Water freezes at 0 °C and boils at 100 °C.
A soluble solid, like salt or sugar, dissolves in water to make a solution. An insoluble solid, like sand, does not dissolve.
Separate mixtures by sieving (solids of different sizes), filtering (an insoluble solid from a liquid), evaporating (a dissolved solid from a solution) or with a magnet.
Reversible changes can be undone (melting, freezing, dissolving). Irreversible changes make new materials (burning, cooking an egg, rusting).

Property: What a material is like, e.g. hard, flexible, transparent or magnetic.
Conductor: A material that lets heat or electricity pass through it easily.
Insulator: A material that does not let heat or electricity pass through it easily.
Soluble: Able to dissolve in a liquid, like sugar in water.
Solution: The mixture made when a substance dissolves in a liquid.
Evaporation: When a liquid changes into a gas.
Condensation: When a gas cools and changes into a liquid.
Irreversible change: A change that makes a new material and cannot be undone.

How could you get clean sand and salt back from a mixture of sand, salt and water?

Stir the mixture so all the salt dissolves. Sand is insoluble, so it does not dissolve.
Filter the mixture: the sand stays in the filter paper and the salt solution passes through.
Leave the sand to dry. Heat the salt solution, or leave it somewhere warm, so the water evaporates.
Answer: filtering removes the sand, and evaporating the water leaves the salt behind.

💡 Test tip

For separating questions, ask: is the solid dissolved (evaporate), insoluble (filter), a different size (sieve) or magnetic (use a magnet)?

Test yourself8 questions from a bank of 24. A new mix every time.