Explain that today is an observation task: students watch a series of demonstrated changes and record careful, scientific observations, then classify each. This is assessed work aligned to the Observing chemical change task, so model the standard expected.
Demonstrate one change (e.g. melting butter) and think aloud how to fill the results grid to a high standard:
Contrast a weak entry ("the butter melted") with a strong one ("the solid butter turned to clear yellow liquid when heated; cooling would turn it solid again, so it's reversible — no new substance"). Set the expectation that every box is justified.
Work through the first demonstration together so the recording routine is shared, then run the remaining demos as independent observation.
Suggested demonstration sequence (vary to suit equipment): melting butter, toasting bread, popping popcorn, melting then refreezing ice, tearing/burning paper. After each, pause briefly for students to complete that row before moving on.
For one demo mid-sequence, model the metacognition aloud: "Which signs am I looking for here? Is anything new being made?" — then hand the thinking back to the students for the rest.
Students independently complete the Observing chemical change results grid for the full sequence of demonstrations. For each change they record:
- a detailed observation;
- the classification (reversible / irreversible) with a justification;
- whether a new substance formed and how they can tell;
- one safety risk and how to reduce it.
Circulate to check classifications and risk statements without giving answers. Collect grids as assessment evidence.
Close (last 5 min): review the correct classifications as a class so students get immediate feedback.