Carbon Dioxide

This demonstration will show that carbon dioxide is more dense than air, and will be drawn to the bottom of a container by the force of gravity.

Time requirement: 15 minutes as a demonstration. The demonstration will take more time if a fire extinguisher is not available.



  1. Discharge a one-second blast of carbon dioxide from the fire extinguisher (if available) into the fish tank. Place the lid on the tank. If an extinguisher is not available, add a mixture of one part baking soda to three parts vinegar to the bottom of the tank. The amounts necessary to generate enough gas for your tank depends on the size of the tank.
  2. Remove the lid and blow bubbles into the tank. Be careful not to disturb the CO2 gas in the tank.
  3. Observe what happens to the bubbles in the tank.

Observation questions

  1. Describe what happened when the bubbles were added to the tank.
  2. Why did the bubbles not fall to the bottom of the tank?
  3. What makes the carbon dioxide sink to the bottom of the tank?
  4. What would happen if another gas were added to the tank which was more dense than air but less dense than carbon dioxide?
  5. How did the size of the bubbles affect the way they reacted when they were introduced to the tank?
  6. If no more carbon dioxide were added to the tank, would the bubbles continue to float on the carbon dioxide? Why???

Last updated: August 27, 1997
Joe Twicken /
Rob Wigand