Turn your students into science detectives with this NO PREP, engaging, real-world investigation focused on the Law of Conservation of Mass. In this case file activity, students analyze mass measurements, examine gas formation data, compare open and closed systems, evaluate dissolving observations, rank possible causes, and build a scientific case to solve the mystery of why mass sometimes appears to disappear during chemical reactions.

Instead of passively reading about conservation of mass and chemical reactions, students actively investigate, analyze patterns, and reason through the evidence to uncover how matter moves during reactions without being created or destroyed. This activity makes chemical change, particle rearrangement, and system boundaries interactive and easy to understand while strengthening critical thinking and literacy skills.

✅ NO PREP, no formatting, no issues. Simply download and go. Includes all instructions, answer key, rubric, and background reading students need to solve the case. This mystery is included inside my Chemistry in Everyday Life Mystery Activity Bundle.

10-Part Activity Breakdown

Part 1 – Mission Briefing: Students are introduced to a case involving chemical reactions where the measured mass appears to decrease after bubbling and dissolving occur.

Part 2 – Background Reading: Students build foundational knowledge about the Law of Conservation of Mass, chemical reactions, particle rearrangement, open vs closed systems, and gas formation.

Part 3 – Evidence Log: Students examine 10 detailed evidence cards related to initial mass measurements, open-container mass loss, gas production, balloon expansion, dissolving solids, temperature changes, and closed-system comparisons.

Part 4 – Suspect Ranking: Students rank possible explanations (gas escaping, open systems, evaporation, dissolving particles, measurement limits) and justify their reasoning using scientific evidence.

Part 5 – Pathway Tracking: Students trace how matter moves from reactants → particle rearrangement → product formation → gas escape → measured mass change.

Part 6 – Impact Analysis: Students analyze how particle rearrangement, system boundaries, and gas movement affect measured mass.

Part 7 – The Big Question: Students explain why matter sometimes appears to disappear during chemical reactions using evidence from the case.

Part 8 – CER Writing: Students construct a scientific argument using Claim–Evidence–Reasoning.

Part 9 – Solutions & Action Plan: Students propose strategies for improving measurement accuracy and designing better experiments.

Part 10 – Reflection: Students reflect on how conservation of mass explains chemical reactions in everyday life.

What Students Will Learn

• What the Law of Conservation of Mass states
• How atoms rearrange during chemical reactions
• Why mass must remain constant in a closed system
• How gas formation affects measurements in open systems
• Why dissolving does not destroy matter
• The difference between open and closed systems
• How particle movement explains observable changes
• How to use Claim–Evidence–Reasoning (CER) to support scientific explanations
• How chemistry explains what appears to be “missing” matter

This activity blends chemistry, environmental science, Earth science, critical thinking, and literacy skills into one high-interest, structured lesson that keeps students thinking like real-world chemical investigators.

This Mystery Is Perfect for:

• Chemistry in Everyday Life units
• Chemical reactions lessons
• Law of Conservation of Mass lessons
• Physical vs chemical change review
• Physical science classes
• Sub plans, review days, or project-based learning

No prep, no formatting, no issues.

Simply download, print (or upload to your class site) and you're all set.

What’s Included

• A complete student case file with guided worksheets for every step of the investigation
• 10 detailed evidence cards based on real-world chemistry issues --> Evidence cards include two versions: one with images and one without images
• A full teacher answer key with sample responses and grading support
• A full marking rubric that covers all key aspects of the mystery activity

Why Teachers Love This Resource

• Fully structured and print-and-go – Everything is ready to use with clear directions and built-in scaffolding
• High engagement without extra classroom management – The detective format naturally hooks students
• Real-world relevance students immediately understand
• Builds both science and ELA skills – Includes analysis, explanation, and CER writing
• Flexible for any schedule – Use in one class period, over two days, or as a mini-project

Time Required

• 2 class periods
• Can be extended into a 3-day mini-project

The following Mystery Activities can be found inside my Chemistry in Everyday Life Mystery Activity Bundle.

1. The Acid Rain Mystery
2. The Household Cleaning Products Reaction Mystery
3. The Conductivity Case Mystery
4. The Energy Release Mystery
5. The Phase Change Puzzle Mystery
6. The Missing Mass Mystery
7. The Ozone Layer Mystery
8. The Plastic Breakdown Mystery
9. The Solubility Surprise Mystery
10. The Spoiled Food Mystery

Google Classroom and Distance Learning Ready

• This resource is perfect for in-class or distance learning and integrates seamlessly with Google Classroom.
• It automatically creates a copy of the reading and places it directly into your Google Drive with a single click.
• Purchase → Open → Click → Assign to your students
• The reading also includes a Microsoft Word and PDF version.
• Having all three options allows you to assign the activity without worrying about formatting issues, and ensures access for all students regardless of device or learning environment.

No prep, no formatting, no issues. Simply download, print (or upload), and you're all set.

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If you have any questions please feel free to send me an email - devon@teachwithfergy.com