Science · Year 8

Active learning ideas

Sublimation and Deposition

Active learning helps Year 8 students grasp sublimation and deposition because these abstract phase changes become visible when students observe real substances like dry ice and iodine. Hands-on rotations let students see mass loss without liquid, making the particle model concrete instead of theoretical.

• ACARA Content Descriptions
• AC9S8U04

• 25–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Inquiry Circle
• 30 min · Small Groups

Demo Station: Dry Ice Sublimation

Place dry ice chunks in an open container and observe fog formation and mass loss over time. Students measure initial and final mass, note temperature changes, and sketch particle movement. Discuss why no liquid forms.

Explain the process of sublimation and provide examples.

Facilitation Tip

During the Dry Ice Sublimation demo, place a small piece on a balance and have students record mass before and after to visibly connect particle escape with weight loss.

What to look for

Provide students with two scenarios: one describing dry ice producing fog, and another describing frost forming on a window. Ask them to: 1. Identify which scenario demonstrates sublimation and which demonstrates deposition. 2. Briefly explain the particle behavior involved in each.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Inquiry Circle
• 45 min · Pairs

Lab Rotation: Iodine Vapour

Heat iodine crystals gently in a test tube over a water bath; observe purple gas forming and condensing on cool surfaces. Rotate groups to record observations, draw before-and-after diagrams, and compare to melting wax. Clean up with ventilation.

Compare sublimation with melting and boiling.

Facilitation Tip

In the Iodine Vapour lab, ensure students seal test tubes properly and hold them in warm water to clearly observe purple vapour forming crystals on cooler surfaces.

What to look for

Pose the question: 'Under what conditions would you expect a substance like iodine to sublime more quickly?' Facilitate a class discussion where students use the particle model to justify their predictions, considering factors like temperature and pressure.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Inquiry Circle
• 40 min · Small Groups

Prediction Challenge: Frost Formation

Expose cold metal cans to humid air overnight; students predict deposition sites and measure frost thickness next day. Groups compare results, link to particle slowing, and test variables like humidity.

Predict conditions under which sublimation is more likely to occur.

Facilitation Tip

For the Prediction Challenge, show students a frosty window and a container of solid air freshener, asking them to predict which will show deposition and why before testing predictions.

What to look for

Present students with a diagram showing particles in different arrangements and energy levels. Ask them to label the processes of sublimation and deposition on the diagram and write a short sentence explaining the energy change required for each.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 04

• Inquiry Circle
• 25 min · Pairs

Model Building: Phase Change Cards

Provide cards showing solids, gases, and arrows; students sort into sequences for sublimation, deposition, melting. Pairs justify arrangements with particle explanations and present to class.

Explain the process of sublimation and provide examples.

Facilitation Tip

During Model Building, provide colored cards for each phase and energy arrows so students physically arrange them to show sublimation and deposition processes.

What to look for

Provide students with two scenarios: one describing dry ice producing fog, and another describing frost forming on a window. Ask them to: 1. Identify which scenario demonstrates sublimation and which demonstrates deposition. 2. Briefly explain the particle behavior involved in each.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

A few notes on teaching this unit

Teach this topic by starting with familiar examples before moving to particle-level explanations. Avoid overwhelming students with too many new terms at once. Research shows that modeling particle behavior with simple diagrams and real-time observations helps students anchor abstract concepts in concrete experiences.

Students will confidently distinguish between sublimation and deposition, describe particle behavior for each, and predict conditions that favor these changes. Success shows when students use evidence from activities to explain their reasoning clearly.

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Watch Out for These Misconceptions

• During Demo Station: Dry Ice Sublimation, watch for students assuming solids must melt before becoming gas.

  Use the dry ice balance setup to show mass loss without liquid residue. Ask students to calculate the mass change and connect it to particles escaping the solid, directly addressing the misconception with evidence.

• During Lab Rotation: Iodine Vapour, watch for students believing sublimation only happens at very low temperatures.

  Have students test iodine at room temperature and slightly warmed water. Ask them to compare rates and explain how energy affects vapour pressure, using their observations to correct the misconception.

• During Prediction Challenge: Frost Formation, watch for students equating deposition with freezing.

  Ask students to compare frost on a window with ice on a car windshield, using their observations to identify that deposition involves gas to solid without a liquid phase, while freezing involves liquid to solid.

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Methods used in this brief

• Inquiry Circle