All lessons › Change detectives › Lesson 3
Australian primary science · Years 5–6 · Lesson 3 of 6
Where did the sugar go?
Inquiry question: Stir sugar into water and it seems to vanish. Has it gone?
Check practical materials
Fair testing
What students learn
Dissolving makes a solution; the dissolved substance is still there, spread through the liquid.
Success criteria
- I can explain what happens to sugar when it dissolves.
- I can plan a fair test that changes only one variable.
- I can use mass as evidence that the sugar is still there.
Preparation and materials
Before this lesson: Reversible changes of state (lesson 2).
- Kitchen scale — 1 (class demonstration)
- Clear cups — 26 (2 per pair)
- Sugar cubes and granulated sugar — 1 box each
- Teaspoons — 13
- Jugs of cold and warm tap water (warm prepared by teacher, below 50°C) — 4 of each
- Timers — 13
- Measuring cups or 100 mL measures — 13
- Saucer of salt water for the windowsill — 1
Teacher setup
- Prepare jugs of cold and warm water.
- At the end of the lesson, set up the salt-water saucer on a sunny windowsill.
Safety and adaptations
- Warm water below 50°C, poured by the teacher.
- No tasting.
Review your school policies and curriculum requirements before teaching.
How to investigate
The lesson sequence should leave pupils with evidence to interpret, not only an activity to finish.
- Choose one variable to change: water temperature, stirring or sugar size.
- Complete the plan: change, measure, keep the same.
- Run two cups at the same time. Time how long until no sugar is visible.
- Repeat once if there is time.
- Help set up the salt-water saucer for next lesson.
Teacher modelling prompt
Weigh a cup of water and a separate pile of sugar, then stir the sugar in and weigh again: the total doesn’t change. Then plan aloud: “I will change the water temperature, measure the time to dissolve, and keep the amount of water, amount of sugar and stirring the same.”
Record and explain evidence
Recording question: What makes sugar dissolve faster?
| Cup | What was different | Trial 1 (s) | Trial 2 (s) |
|---|---|---|---|
| ________________ | ________________ | ________________ | ________________ |
Example recording headings; record actual observations, including inconclusive results.
Discussion prompt
Which claim is right, and how would you fix Ali’s test?
Check understanding
What should pupils know? Where did the sugar go when it dissolved?
Explain with evidence: Ali stirred cup A, which had cold water. He used hot water in cup B and did not stir it. Cup B dissolved faster. Why can’t he tell what made the difference?
Apply the idea: A drink powder is stirred into water and disappears. How could you show it is still there without tasting it?
Teacher answer guidance and saved classroom work are available through the main lesson experience where supported.