Scientific Inquiry and the Natural World · 6th Class

Active learning ideas

Conservation of Mass

Active learning lets students see the Law of Conservation of Mass in action, not just read about it. When they seal reactants in a bag and watch the mass stay the same, the abstract concept becomes tangible and memorable.

• NCCA Curriculum Specifications
• NCCA Junior Cycle Science Specification, The Chemical World: CW5
• NCCA Junior Cycle Science Specification, The Chemical World: CW6

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

Activity 01

• Inquiry Circle
• 30 min · Small Groups

Sealed Bag Reaction: Baking Soda and Vinegar

Provide each small group with a zip-lock bag, baking soda, and vinegar. Students measure and record reactant masses, seal the bag after adding vinegar, observe the inflation from gas, then reweigh. Groups compare before-and-after data and calculate differences.

Explain the Law of Conservation of Mass.

Facilitation Tip

During the Sealed Bag Reaction, remind students to seal the bag tightly before weighing to prevent leaks that could skew results.

What to look for

Provide students with a scenario: '5 grams of substance A reacts with 10 grams of substance B in a sealed container. What will be the total mass of the products?' Ask students to write their answer and one sentence explaining their reasoning.

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

Activity 02

• Inquiry Circle
• 35 min · Small Groups

Steel Wool and Vinegar: Mass Check

Groups place steel wool in a flask, add vinegar, seal with a balloon. Weigh the setup before and after the reaction causes the balloon to inflate. Students predict outcomes, measure, and graph results to verify conservation.

Analyze experimental data to demonstrate the conservation of mass.

Facilitation Tip

For the Steel Wool and Vinegar experiment, have students shake the container gently to expose all surfaces to vinegar without breaking the seal.

What to look for

Give students a card with a simple chemical reaction (e.g., baking soda + vinegar). Ask them to draw a diagram of a closed system for this reaction and label the reactants and products. Then, ask them to write one sentence stating what the Law of Conservation of Mass predicts about the total mass.

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

Activity 03

• Inquiry Circle
• 45 min · Small Groups

Dissolving vs Reacting: Weighing Stations

Set up stations with salt dissolving in water and Alka-Seltzer reacting in sealed bottles. At each, students weigh before, perform change, weigh after, and note if mass conserved. Rotate and compile class data.

Predict the mass of products formed given the mass of reactants in a closed system.

Facilitation Tip

At the Dissolving vs Reacting stations, place balances near each station so students can immediately weigh changes and discuss differences in real time.

What to look for

Pose the question: 'Why is it important for experiments demonstrating the conservation of mass to be conducted in a closed system?' Facilitate a class discussion, guiding students to articulate the role of open versus closed systems in preventing mass loss or gain.

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

Activity 04

• Inquiry Circle
• 25 min · Pairs

Prediction Challenge: Reactant to Product

Present data cards with reactant masses for common reactions. In pairs, students predict product masses, justify using the law, then test one prediction with a demo reaction and verify.

Explain the Law of Conservation of Mass.

Facilitation Tip

In the Prediction Challenge, ask students to jot down predictions before seeing the reactants to encourage critical thinking before confirmation.

What to look for

Provide students with a scenario: '5 grams of substance A reacts with 10 grams of substance B in a sealed container. What will be the total mass of the products?' Ask students to write their answer and one sentence explaining their reasoning.

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

A few notes on teaching this unit

Teaching this topic works best when students do the weighing themselves and discuss why numbers sometimes seem to change. Avoid relying solely on textbook examples, as hands-on trials build stronger conceptual understanding. Research shows that students retain the principle better when they actively confront and correct their own misconceptions through direct measurement.

Students will confidently explain that mass stays constant in closed systems by referencing their own measurements and observations. They will also be able to identify when mass appears to change and why that happens in open systems.

---

Watch Out for These Misconceptions

• During the Sealed Bag Reaction activity, watch for students who expect the bag to feel lighter after the reaction because they see bubbles form.

  Use the sealed bag reaction to show that even though gas forms and the bag inflates, the total mass before and after remains the same when measured on a balance.

• During the Steel Wool and Vinegar activity, watch for students who believe the steel wool gains mass because it changes color or texture.

  Have students weigh the sealed container with steel wool and vinegar before and after the reaction to observe that the total mass stays constant, even as the steel wool rusts.

• During the Burning always reduces mass unit, watch for students who generalize that any reaction involving fire or smoke reduces mass.

  Use candle-jar trials to show that in a closed system, the ash and trapped gases together equal the original candle's mass, proving conservation.

---

Methods used in this brief

• Inquiry Circle