lesson
Change one relevant condition
1 · Learn
To compare dissolving fairly, define the question. If comparing two substances in water, keep the amount of water, temperature, sample amount and stirring method as similar as possible.
Dissolving rate and how much can dissolve are different questions. A substance dissolving quickly does not by itself prove that a larger maximum amount will dissolve.
2 · Worked example
I time equal small samples in equal water volumes with the same stirring method. I repeat rather than selecting only the fastest result.
3 · Your turn
Why is changing both water temperature and stirring speed an unclear test of temperature alone?
Check your answer
Either change could affect the result, so the test would not isolate temperature's effect.
4 · Apply your learning
Plan a safe cold-water comparison and a results table. Identify one limitation and an appropriate repeat reading.
Adult guidance and safety
Use adult-approved safe substances, no hot liquids or tasting. Do not perform an investigation without the adult's approval.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
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