Conservation of Matter in Changes

Active experiments help students see conservation of matter in action, making abstract particle ideas concrete. When students measure mass before and after changes, they build trust in evidence over assumptions, which is essential for grasping this principle.

• Grade 5
• Science
• 4 activities
• 25 min–45 min

Learning Objectives

1. Calculate the total mass of reactants before and after a physical change, such as dissolving, to demonstrate conservation of mass.
2. Analyze experimental data from a sealed chemical reaction, like baking soda and vinegar, to verify that the total mass remains constant.
3. Construct an argument, supported by evidence from investigations, explaining why matter cannot be created or destroyed during observable changes.
4. Compare the mass of substances before and after a physical change and a chemical change, identifying similarities in mass conservation.
5. Explain how the arrangement and movement of particles change during physical and chemical changes while the total number of particles remains constant.

Inquiry Circle

⏱ 35 min·Small Groups

Precision Weighing: Dissolving Salt

Provide beakers with 100 mL water; students record mass, add 20 g salt, stir until dissolved, then reweigh. Have them evaporate water to recover salt and weigh again. Groups compare results and graph mass changes.

Prepare & details

Explain how the total mass of substances remains constant during a physical change.

Facilitation Tip: At the Station Rotation, place a timer at each station so students stay on task and rotate smoothly.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

Inquiry Circle

⏱ 25 min·Pairs

Sealed Bag Reaction: Baking Soda and Vinegar

In zip-top bags, students measure masses of baking soda and vinegar separately, seal together to react, then weigh the full bag. They feel the gas form and note total mass remains constant. Discuss particle rearrangement.

Prepare & details

Analyze experimental data to demonstrate the conservation of matter in a chemical reaction.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

Inquiry Circle

⏱ 40 min·Individual

Ice to Water Cycle

Students mass ice cubes in a container, let melt at room temp, reweigh water, then freeze and weigh ice. Extend by adding food coloring to track particles. Record observations in science notebooks.

Prepare & details

Construct an argument for why matter cannot be created or destroyed.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

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

Stations Rotation

⏱ 45 min·Small Groups

Stations Rotation: Change Types

Set up stations for melting chocolate, dissolving sugar, effervescent tablets in water, and candle in jar (mass before/after burn). Groups rotate, measure at each, compile class data on mass conservation.

Prepare & details

Explain how the total mass of substances remains constant during a physical change.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Teaching This Topic

Teachers should emphasize repeated measurements to build trust in the law of conservation, rather than relying on single demonstrations. Avoid rushing to explanations before students have collected their own data, and always link observations back to particle behavior. Research suggests hands-on weighing and sealed systems reduce misconceptions about mass loss.

What to Expect

Students will use balances to track mass before and after changes, explain why mass stays the same using particle language, and apply their observations to new scenarios. Success looks like confident predictions and clear reasoning tied to their data.

Watch Out for These Misconceptions

Common Misconception

During Precision Weighing, watch for students who believe the dissolved salt disappears, reducing total mass.

What to Teach Instead

Ask students to check the balance again after dissolving and point to the salt particles still present in the water, reinforcing that mass stays constant even when particles spread out.

Common Misconception

During Sealed Bag Reaction, watch for students who think mass is lost as gas escapes.

What to Teach Instead

Have students feel the bag for pressure changes and reweigh it immediately to show the total mass includes the gas produced.

Common Misconception

During Ice to Water Cycle, watch for students who think melting creates new matter.

What to Teach Instead

Guide students to compare the mass of ice and water in identical containers, then ask them to draw particle models to explain the same particles in a different arrangement.

Assessment Ideas

Quick Check

After Precision Weighing, provide the scenario: 'You mix 10g of salt with 100g of water in an open beaker and stir until dissolved.' Ask students to predict the total mass of the solution and explain whether the mass of the remaining salt would be less than 10g if water evaporated. Collect responses to identify gaps in reasoning.

Exit Ticket

After Sealed Bag Reaction, give students two sealed bags: Bag A with baking soda and vinegar, Bag B with only water. Students predict, weigh, and record masses, then explain why Bag A’s mass did not change and Bag B’s mass stayed the same. Review exit tickets to assess understanding of sealed systems.

Discussion Prompt

During Ice to Water Cycle, pose the question: 'Imagine you burn a log in a fireplace. The ashes weigh much less than the log. Does this mean matter was destroyed?' Have students use particle models to explain where the rest of the mass went, then circulate to listen for correct particle language and conservation reasoning.

Extensions & Scaffolding

• Challenge students to design a new conservation experiment using sugar or citric acid instead of salt.
• Scaffolding: Provide pre-labeled beakers and digital scales with step-by-step guides for struggling groups.
• Deeper exploration: Have students research how conservation of matter applies to recycling or composting, then present findings.

Key Vocabulary

Conservation of Matter	The principle stating that the total amount of matter in a closed system remains constant over time, meaning matter cannot be created or destroyed during physical or chemical changes.
Physical Change	A change in the form or appearance of a substance, but not its chemical composition. Examples include melting, freezing, dissolving, and changing shape.
Chemical Change	A change that results in the formation of new chemical substances with different properties. Examples include burning, rusting, and cooking.
Reactant	A substance that takes part in and undergoes change during a reaction. Reactants are on the left side of a chemical equation.
Product	A substance that is formed as a result of a chemical reaction. Products are on the right side of a chemical equation.