Lesson overview
Physical and chemical changes: Did a new substance form?
Heat white candle wax and green copper(II) carbonate in turn, with the gas from each tube bubbling through limewater. Watch what melts, what turns black and which limewater turns milky, decide which tube made a new substance and what proves it, then sort everyday changes by whether the particles stay the same.
Suggested sequence
- Lesson 1 · Heat it, then test it. Heating wax and copper(II) carbonate: a physical and a chemical change, clues and proof. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Same particles, or new ones? Everyday physical and chemical changes explained with particles. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- End of module · final check. 4 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 3 questions, 15 min, lesson closed.
Learning goals
Part 1: Heat it, then test it
- Decide from evidence whether a new substance was made: a physical change makes no new substance (a change of state, shape or mixing); a chemical change makes one or more new substances; tell clues from proof (6.1.1)
Part 2: Same particles, or new ones?
- Decide from evidence whether a new substance was made: a physical change makes no new substance (a change of state, shape or mixing); a chemical change makes one or more new substances; tell clues from proof (6.1.1)
- Identify physical and chemical changes in everyday and laboratory examples and describe the difference in terms of particles: the same particles, or atoms joined in new ways into new particles (6.1.1)
Misconceptions to listen for
- “It is physical because it can be changed back by cooling.” — It is physical, but not for that reason: some chemical changes can be turned back too. The reason is that the solid at the end has the same properties, so no new substance was made.
- “The clear liquid looks different, so it is a new substance.” — The clear liquid is the same oil in another state. When it sets, the tests show the same properties as before.
- “Anything that changes state when it is warmed is a chemical change.” — The oil changed state when it was warmed, but it is still coconut oil. Heating can cause a physical or a chemical change.
- “Bubbles show that a new substance was made.” — Fizzing shows that a gas comes off, not which gas. The squeaky-pop test identifies it.
- “A temperature change proves a chemical change.” — Some substances make water warmer or colder just by dissolving in it. A temperature change is a clue, not proof.
- “A solid that gets smaller has turned into a new substance.” — A solid that dissolves gets smaller too, and it is still the same substance. Getting smaller is a clue only.
- “Any solid that appears in a liquid is a new substance.” — The potassium nitrate was dissolved in the water before the crystals appeared. A solid can come out of a solution with no new substance made.
- “A clue is the same as proof.” — A clue says that a chemical change may have happened. Proof shows a substance at the end that was not there at the start.
- “A solid left at the end is a new substance.” — This black powder is the manganese(IV) oxide that was put in. A solid at the end shows a new substance only if it has properties that nothing at the start had.
- “A colour change proves a chemical change.” — The food colouring changes the colour of the water, but the dye particles only spread out. It is still the same dye.
Scope
Physical and chemical changes (6.1 Core 1): identifying physical and chemical changes and describing the difference in terms of whether any new substances have been made. Rates of reaction are in the next module, reversible reactions in 6.3 and the tests for gases in topic 12.