A CAROLINA ESSENTIALS INVESTIGATION

Law of Conservation of Mass

Time Icon

Total Time

  • Prep: 30 mins
  • Activity: 30 mins

Physical Science

grade icon

Grade Level

9-12 High School

Introduction

This inquiry investigation of the law of conservation of mass includes a brief review of physical and chemical changes and examples of conservation of mass for both processes. Use the investigation as a discovery-inquiry activity to introduce conservation of mass or as a confirmatory investigation.

Download Teacher Notes
Download Student Worksheet

Phenomenon

How do we know mass is conserved? Your teacher will provide a simple demonstration.

Teacher preparation: Pre-cut a 6–8-in square of aluminum foil. Set a digital balance under a document camera so students can see the balance and its read-out. Weigh the foil flat, folded, and balled up. Discuss results and what conservation means from a physical science perspective.

Mass of aluminum foil flat: __________________________________________

Mass of aluminum foil folded: _______________________________________

Mass of aluminum foil balled up: ____________________________________

Did changing the shape of the foil affect the mass? Was mass conserved?

Essential Question

How can the law of conservation of mass be demonstrated for physical and chemical changes?

Investigation Objectives:

  1. Explain the law of conservation of mass for physical and chemical changes.
  2. Demonstrate the law of conservation of mass mathematically.
  3. Recognize the difference between physical and chemical changes.

Next Generation Science Standards* (NGSS)

HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

SCIENCE & ENGINEERING PRACTICES

Developing and Using Models

  • Develop a model based on evidence to illustrate the relationships between systems or components of a system.

DISCIPLINARY CORE IDEA

PS1.A: Structure and Properties of Matter

  • The law of conservation of mass models how reactants are broken down and reformed to make products so total mass remains constant.

CROSSCUTTING CONCEPTS

Energy and Matter: Flows, Cycles, and Conservation

  • The law of conservation of mass tracks the movement of atoms within a system.

Materials Needed

Recommended Safety

Wear gloves and goggles and practice safe laboratory procedures.

Teacher Prep and Disposal

Calcium carbonate, the precipitate, should be collected from all groups and disposed of in the manner prescribed by local, state and federal guidelines. Do NOT flush it down the sink.

Student Procedures

Procedure A: Ice and Water

    1. Place the beaker or cup on the balance, demonstrate how to zero or tare balances, record the mass in grams, and then zero or tare the beaker.
    2. Remove the cap from the test tube. Fill the test tube half full of chipped ice. Replace the cap.
    3. Weigh the capped test tube in the beaker or cup on the balance. Record the mass in table A.
    4. Place the test tube on your lab table and continue to make observations until the ice has melted.
    5. Reweigh the capped tube in the beaker or cup after the ice has melted. Record the mass in table A.
    6. To determine the change in mass, take the mass of the water with tube and subtract the mass of the ice with tube.
    7. Record the change in mass in table A.

Procedure B: CaCl2 and Na2CO3

  1. Place the beaker or cup on the balance and zero or tare the balance.
  2. Using a clean graduated cylinder, measure 1.5 mL of calcium chloride solution (CaCl2).
  3. Pour the calcium chloride into a test tube.
  4. Wipe off the outside of the tube with a paper towel to remove any excess. Place the tube in the beaker or cup on the balance.
  5. Using a clean graduated cylinder, measure 1.5 mL of sodium carbonate solution (Na2CO3).
  6. Pour the sodium carbonate into the test tube.
  7. Wipe off the tube with a paper towel to remove any excess. Place the tube in the beaker or cup on the balance.
  8. Record the mass of both tubes with solutions in table B.
  9. Pour the calcium chloride into the test tube that contains sodium carbonate and record your observations in table B.
  10. After combining the calcium chloride and sodium carbonate, reweigh both test tubes in the beaker or cup. Record the mass in table B.
  11. To determine the change in mass, take the nal mass of the test tubes and subtract the beginning mass of the test tubes. Record the change of mass in table B.
Teacher Preparation and Tips
  1. If ice cubes are the only type of ice available, wrap cubes in a towel and break them into pieces with a hammer so they will fit into the tube.
  2. Prepare enough volume of each solution for the total number of lab groups. Add an additional 10 to 20% more volume in case students make mistakes.
  3. See Carolina’s Solution Preparation Manual for instructions on preparing molar solutions.
  4. Demonstrate how to zero or tare balances.
  5. Review and discuss with students what physical and chemical changes are and what type of evidence they may observe.
  6. Keep ice in a well-insulated cooler to minimize melting.
  7. Emphasize that caps must be on the tubes securely. No leaks. Remind students that the mass of the beaker or cup should not be included in the recorded mass.
  8. Have all solutions prepared, labeled, and in a central location.
  9. Instruct students that M is molarity, which is a unit of concentration. Demonstrate how to pour liquids.
  10. This is a good time to introduce the vocabulary and concepts of reactants and products.
  11. Emphasize to students that the graduated cylinder must be clean or a reaction will take place in the cylinder.
  12. If students spill a solution, wipe it up immediately with a paper towel and dispose of the paper towel in the trash.
  13. If students spill a solution, they will need to start over.

Data and Observations

See the student worksheet. Answers will vary but should be close.

Analysis and Discussion

Analysis and Discussion

  1. Use the data to explain whether mass was conserved in procedures A and B.

    Mass should be conserved in both procedures. The initial mass was the same as the final mass.

  2. Translate your explanation above into a mathematical statement.

    mass before = mass after
    mass(i) = mass(f)
    mass(reactants) = mass(products)

  3. Create a particle diagram for each process.

    the particles of the reactants need to be balanced with the products

  4. Identify the processes above as a chemical change or physical change, and state the observations used to make the identification.

    A. Physical: Water did not change its identity, only its state of matter.
    B. Chemical: Two new products and a precipitate were formed.

Carolina ChemKits®: Law of Conservation of Mass Kit image
Carolina ChemKits®: Law of Conservation of Mass Kit

Buy the Kit

Buy the Kit
Materials

Reference Kits

Helpful Links

*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.

Back to Top

About The Author

Carolina Staff

Carolina is teamed with teachers and continually provides valuable resources–articles, activities, and how-to videos–to help teachers in their classroom.

See author's posts

Login / Register
Shop Science

Newsletter Signup

Get the latest news, free activities, teacher tips, product info, and more delivered to your inbox.