Conservation of Mass

Lesson Context and Curriculum Alignment

This 13-minute lesson is targeted at Year 7 Science students in Australia. It aligns with the content description in the Australian Curriculum: “ACSSU113: Some of Earth’s resources are renewable, but others are non-renewable” and “ACSSU225: Scientific understanding, including models and theories, is refined over time through a process of review.” The selected focus within this context is the Conservation of Mass, which introduces students to the idea that during physical and chemical changes, the mass of substances before and after remains constant.

This lesson is designed for a small class of 7 students and includes hands-on, interactive activities to cater to diverse learning styles with an 'inquiry-based' approach.

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Lesson Objectives

By the end of this short, 13-minute lesson, students will be able to:

1. Define the principle of conservation of mass in simple terms.
2. Apply the principle to real-world scenarios and basic chemical reactions.
3. Conduct a hands-on activity to observe and confirm the conservation of mass.

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Lesson Plan

1. Introduction (2 minutes)

• Focus Statement: Start with a statement to grab attention – "What if I told you that nothing ever disappears completely, not even that piece of toast you burnt this morning?"
• Ask the class: “What do you think happens to the mass of something when it burns, melts, or changes into something else?” [Encourage brief answers without diving into explanations, sparking curiosity.]
• Define Conservation of Mass: "In any closed system, the mass of substances before and after a change stays constant – it just might look different!"

Write the statement on the board: Mass is never lost, only transformed.

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2. Hands-On Activity (7 minutes)

Activity Title: "Is the mass REALLY conserved?"

Materials:

• Digital scale
• Two clear zip-lock bags (per two students)
• Effervescent tablets (like Berocca or Alka-Seltzer)
• Plastic cups half-filled with a liquid (preferably water)

Activity Steps:

1. Students will work in pairs. Hand out materials to each pair.

2. Instruct them to:

   • Weigh the zip-lock bag containing the cup of liquid (without opening it) and record the weight on the worksheet.
   • Add an effervescent tablet to the cup via the zip-lock bag (so nothing escapes the system). Observe the fizzing reaction inside.
   • Once the reaction subsides (after about 10–30 seconds), weigh the contents again without opening the bag.

   Note: Students observe that the mass remains the same, even though the substances have visibly changed (tablet dissolving, bubbles forming).

3. Facilitate a short whole-class discussion (1–2 minutes):

   • Ask: “Why do you think the mass didn’t change, even though the tablet dissolved?” Guide them to link this observation to the principle of conservation of mass.

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3. Quick Reflection Exercise (4 minutes)

Part 1 (Verbal):
Pose these two questions to think about:

1. "Imagine burning a piece of paper – where does the paper go, and how do you think it relates to conservation of mass?"
2. "Can you think of an everyday example where the conservation of mass might be visible?" (E.g., cooking, melting ice, etc.)

Let each student share one thought briefly.

Part 2 (Worksheet):
Distribute worksheets containing two closed system scenarios with simple diagrams and blank spaces for answers. Example:

Scenario 1: You place ice cubes in a sealed container. The ice melts completely. If the container weighed 500 grams before, what is the total weight of the container after the ice has melted?

• Your Answer: __________ grams

Scenario 2: You seal water and vinegar in a bag, then add bicarb soda. The bag inflates due to the gas produced. Will the mass of the sealed bag before and after the reaction be the same? Why?

• Your Answer: ___________

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Assessment and Differentiated Learning

• Assessment:
  Check students’ final answers on the worksheet to reinforce understanding. Remind them to use the principle of conservation of mass in their justifications.

• Extension for Early Finishers:
  Challenge faster students to explain why the mass of ash and smoke from a burnt log is equal to the original mass of the log.

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Teacher Reflection

Why This Lesson Will ‘Wow’:

1. Engaging the Senses: The activity involves observable reactions (fizzing) and uses hands-on manipulatives.
2. Inquiry-Based Learning: Students witness the concept in action and arrive at the conclusion themselves, making the learning memorable.
3. Real-World Relevance: Questions and scenarios directly relate to everyday phenomena, making science relatable.

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Resources

Materials:

• Digital or manual scales
• Zip-lock bags, effervescent tablets, cups
• Prepared "Reflection Worksheet" for follow-up

Alternative Materials (for budget/resource constraints):

If unavailable, the effervescent reaction can be substituted with similar safe, observable reactions, such as mixing vinegar and baking soda in a sealed container.

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Closing Statement:

"Science shows us that even when it looks like something is gone forever – like steam that escapes or logs that burn – it’s all still there, just rearranged. Nothing ever disappears in our universe, and you’ve just explored one of its most fascinating principles."