What happens when solids and liquids are heated and cooled?

Preparation

• Lesson 5 of this unit should be completed before this lesson.
• Provide some examples of the substances discussed on the student summary i.e. water, milk, honey, wood, fruit, sugar, margarine.
• Collect the equipment needed by the investigation sheet, i.e. 5 identical bars of dairy milk chocolate, thermometer, 1 ovenproof tray, oven, 4 paper plates.
• Preheat the oven to 180 degrees Celcius.

Curriculum links

• Australian Curriculum: ACSSU046, ACSIS053, ACSIS054, ACSIS055, ACSIS057, ACSIS215, ACSIS058, ACSIS060
• NSW Curriculum: ST2-6MW-S, ST2-1WS-S
• Victorian Curriculum: VCSSU059, VCSIS070, VCSIS065, VCSIS066, VCSIS067, VCSIS068, VCSIS069, VCSIS071, VCSIS072
• WA Curriculum: ACSSU046, ACSIS053, ACSIS054, ACSIS055, ACSIS057, ACSIS215, ACSIS058, ACSIS060

Suggested teaching strategies

• Collaborative learning

Introduction

• Though several of the scientific terms are revised in the text, before reading through the student pages, ensure students understand the terms ‘matter’, ‘states of matter’, ‘substance’, ‘solid’, ‘liquid’ etc. if Lesson 1 has not been taught.

Development

• Provide students with printable versions of the student summary and worksheet. Have students complete the worksheet.
• When completing the investigation sheet, have students discuss how they can ensure the test is fair or not (all chocolate bars must be identical).
• The student summary and worksheet should be used together.

Differentiation

• Students can work in a small group or as a whole class for the activity on the investigation sheet.

Conclusion

• Once students have completed their experiment, encourage them to discuss with the rest of the class either teacher-led or students sharing with other groups.

Assessment

Worksheet answers

1. honey, milk, raw egg
2. Answers should indicate that margarine is a solid in the fridge or at room temperature. When heated, it becomes a liquid. When cooled it becomes a solid once more.
3. …a substance changes state and cannot be changed back again…
4. (a) No, irreversible (b) Yes, reversible
5. (a) False (b) False (c) False

Investigation sheet answers

Temperatures will vary, except for the oven which should show it has been preheated to 180 degrees celcius. (Obviously, the students will use the gauge as a guide and not actually use a thermometer!)
A summary of what should happen is provided below. Allow the students to touch the chocolate before recording to hlep them describe what happened. Digital photographs could be taken at appropriate intervals.
(a) The chocolate in the classroom should look the same and remain a solid and be at room temperature to touch.
(b) The chocolate in full sun will melt and become a thick liquid (at an interval depending on how hot the day is), could feel slightl warm if a hot day and be sticky and possibly quite runny to touch.
(c) Depending on the heat of the day, the chocolate may or may not partially or fully melt.
(d) Chocolate will take a very short time to melt. (Don’t allow it to stay too long in oven.) It may even bubble if it reaches boiling point. When first taken out of the oven it will be a runny liquid and quite warm to touch. (Take care it is not too hot for students to touch.)
(e) Chocolate will remain solid and cool to touch.