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Exploring the Laws of Definite and Multiple Proportions (1 Favorite)

LESSON PLAN in Percent Composition, Law of Definite Proportions, Molar Mass, Law of Multiple Proportions. Last updated May 17, 2021.


In this lesson, students will review the concept of percent composition and then apply it to the laws of definite and multiple proportions.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

  • Scientific and Engineering Practices:
    • Using Mathematics and Computational Thinking


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

  • Calculate the percent composition of a substance.
  • Use calculations and explanations to show that the Law of Definite and Multiple Proportions are being followed using data.

Chemistry Topics

This lesson supports students’ understanding of:

  • Molar Mass
  • Percent Composition
  • Law of Definite Proportions
  • Law of Multiple Proportions


Teacher Preparation: 10 minutes
Lesson: 45 minutes to 1 hour


  • Presentation Slides (available for download as PPT and PDF)
  • Student Handout: Lecture Notes
  • Student Handout: Practice Worksheet


  • There are no safety precautions needed for this lesson.

Teacher Notes

  • This lesson includes a PowerPoint presentation to use when reviewing percent composition and introducing the Laws of Definite and Multiple Proportions.
    • There is a “Lecture Notes” handout for students to use during the presentation. It is set up to allow them to take notes and complete sample calculations.
    • The answers throughout the PowerPoint presentation are animated, meaning that they will display only when the teacher clicks on the slide to show them. This feature will not work in the PDF version of the presentation. Note that the answers do not appear on the student handout for the lecture notes.
  • There is also a practice worksheet for students to complete after the lecture. A separate answer key document is available for teacher reference.
  • If you have a class that struggles with mathematical calculations, you might consider having students use different size Lego Bricks or K’NEX Connectors to build the compounds in this lesson.
    • Assign a different size piece to each element.
    • Have students assemble the compounds and take the mass of several of each of the “molecules”.
    • They then break them down and take the mass of each element.
    • Use the data collected to help with student calculations.

For the Student



Use the space next to each slide to take notes and complete the sample problems. Show all of your work for calculations.