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Density of a Gas

Time Frame:
1 class period that runs 70 minutes.

Group Size:
Small Groups


Students will measure the density of a gas using a seltzer tablet to release carbon dioxide.

Main Curriculum Tie:
SEEd - Grade 8 (2017)
Strand 8.1: Matter and energy interact in the physical world 8.1.2

Obtain information about various properties of matter, evaluate how different materials’ properties allow them to be used for particular functions in society and communicate your findings. Emphasize general properties of matter. Examples could include color, density, flammability, hardness, malleability, odor, ability to rust, solubility, state, or the ability to react with water.


  • 2 identical bags (plastic)
  • ring stand
  • clamp
  • medium sized test tube
  • glass tubing
  • plastic tubing
  • 100 mL graduated cylinder
  • bucket
  • goggles
  • Alka Seltzer or generic (much cheaper) stomach aid tablets
  • Worksheet


Instructional Procedures:

  1. “Hook” students by asking them how the density of gas could be measured. If they have had some experience with calculating density they may be able to generate responses concerning volume and mass. Most responses will center around filling a bag with a gas (blowing into it) massing it, and then finding its volume.
  2. Demonstrate this procedure and generate an answer. The volume of the bag can be quickly measured by placing the blown up bag in a large beaker.
  3. Redo this experiment with an empty bag. Because of the very small density of gases, you may discover it makes no difference whether the bag has air or not, most middle school balances cannot easily detect the difference between masses this small.
  4. Explain to students that another way exists to measure the density of a gas and that is explained in the lab they will be doing.
  5. Read the procedures and demonstrate the set up of the lab. The most difficult part is getting the graduated cylinder full of water and upside down in the bucket.
  6. Allow students to work, handing out half a seltzer tablets per group. Do not give them to students at first, it is too easy for them to drop them in the water before they are ready.
  7. As students finish, ask them to post their results on the board or an overhead. The density of carbon dioxide is about .002. If your students can come within a decimal place of this figure, they have done well.
  8. Discuss sources of error, there are lots of them. Allow students to finish with the analysis questions.


Lesson Design by Jordan School District Teachers and Staff.

Utah LessonPlans

Created Date :
Sep 30 2014 09:26 AM