Conservation of Mass Lesson Plan

Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

The law of conservation of mass is an integral concept in your chemistry curriculum. This lesson plan uses a short video, discussions, hands-on activities, and demonstrations to give students a well-rounded introduction to the topic.

Lesson Objectives

By the end of this lesson, students will be able to:

  • State the law of conservation of mass
  • Describe several, everyday examples of conservation of mass
  • Describe how a balanced chemical equation represents conservation of mass


1-1.5 hours

Curriculum Standards


Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.


Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 9-10 texts and topics.


Compare and contrast findings presented in a text to those from other sources (including their own experiments), noting when the findings support or contradict previous explanations or accounts.


  • Erlenmeyer flasks
  • Steel wool
  • Medium-large beakers (to hold reagents)
  • Vinegar
  • Balloons
  • Digital scales, 1 per group
  • Small beakers, 4 per group
  • Lead nitrate solution (can be purchased online)
  • Potassium iodide solution (can be purchased online)
  • Baking soda
  • Hotplate
  • Small pot
  • Un-popped popcorn kernels


  • Begin the class with a demonstration using a piece of steel wool, a beaker filled with vinegar, an Erlenmeyer flask, a balloon and a digital scale:
    • Soak the steel wool in vinegar for about a minute. Remove the steel wool and drain any excess vinegar.
    • Place the steel wool into the Erlenmeyer flask and cover the mouth of the flask with a balloon.
    • Place the system onto a digital scale and note the mass.
    • Ask students to make predictions on what will happen.
    • Leave the flask on the scale and place the entire apparatus to the side. Tell students to make a note of what happens throughout the class. Explain that while they are waiting, they will watch a video on the conservation of mass.
  • Begin the video The Law of Conservation of Mass: Definition, Equation & Examples. Pause at 1:37. To check for understanding, ask the following discussion question:
    • What is the law of conservation of mass?
  • Return to the video, this time pausing at 3:18. Ask students the following questions:
    • According to video, the discovery of the conservation of mass led to what important results?
    • Your ingredients for a batch of shortbread cookies have a mass of 350g. How much mass should your batch of cookies contain after they have been baked?
  • Continue the video. Pause at 4:45. Provide students a simple skeleton equation so they can practice balancing an equation. Ask the following discussion questions:
    • The law of conservation of mass is seen in which type of chemical equation?
    • What is an 'unbalanced chemical equation?'
  • Watch the video to the end.
  • Check for understanding by completing the lesson quiz.

Activity Part 1

  • Return to demonstration from the beginning of the lesson; note the mass of the system.
  • Pass the flask around the room and ask students to make observations. Do they have any possible explanations for what has happened?
  • Provide the skeleton equation for the formation of rust to help them brainstorm.

Activity Part 2

  • Divide the class into groups of four. Provide each group with four, small beakers and a digital scale. Create one or more stations where students can get samples of lead nitrate solution and potassium iodide solution.
  • Have one person from each group take two small beakers and collect some lead nitrate and potassium iodide, one solution in each beaker. They do not need much. Be sure they do not mix the two solutions until after they have massed them with their group.
  • Ask the students to take the beakers containing the solutions and place them both on their scale. Have students note and record the mass.
  • Now, students can pour the contents of one beaker into the other and place both beakers back onto the scale. Have students note the mass.
  • Ask the following questions:
    • How can you tell that a chemical reaction took place?
    • How does this activity show conservation of mass?
  • Provide students with a skeleton equation for the reaction.

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