This experiment demonstrates how a soap bubble can float on an invisible layer of carbon dioxide gas. By generating carbon dioxide from baking powder and water (or dry ice), students explore concepts of gas density.

1. Mix 100 ml (0.42 cup) of water, 1 tablespoon of dish soap, and 1 teaspoon of glycerin in a cup to make a bubble solution.
2. Pour baking powder into a large container (such as a bowl, aquarium, or sink).
3. Add enough vinegar to cover the baking powder and start the fizzing reaction that produces carbon dioxide gas.
4. Allow the reaction to settle - avoid moving the container so the carbon dioxide remains inside.
5. Using a bubble blower or a ring, blow a soap bubble and carefully let it fall into the container.
6. Watch as the soap bubble floats in mid-air on top of the invisible layer of carbon dioxide.
7. Observe how the bubble may rise, swell, or sink slowly as the gases mix over time.

Buoyancy: Floating Bubbles - WSU Physics Videos:

Giant Bubble Floats on CO2 - BBC Earth Science :

📄 Hovering soap bubble - Experiment Archive: https://www.experimentarchive.com/experiments/hovering-soap-bubble/

• Use dry ice and water to produce the carbon dioxide.
• Try using different amounts of baking powder and measure how high the carbon dioxide layer rises (using a lit match to test).
• Compare the behavior of large and small soap bubbles.
• Blow gently into the container to see how air currents affect the floating bubble.
• Pour carbon dioxide from one container into another to see if a bubble can float in the second container.
• Blow clusters of bubbles using multiple straws and observe how they behave on the carbon dioxide surface.

• Do not inhale directly over the container - carbon dioxide can displace oxygen.
• Keep baking powder and soap away from eyes and mouth.
• Handle glycerin and soap carefully to avoid spills and slipping.

• Why does the soap bubble float on carbon dioxide? (The bubble is filled with air, which is less dense than carbon dioxide, so it rests on top of the denser gas.)
• Why is the carbon dioxide invisible? (It does not absorb or reflect visible light.)
• Why does the soap bubble eventually burst or sink? (Carbon dioxide slowly diffuses through the soap film, changing the bubble’s internal gas composition and weight.)
• What role does glycerin play in the bubble solution? (It strengthens the soap film and slows water evaporation, making longer-lasting bubbles.)
• How is this experiment related to the atmosphere and natural gas layers? (It demonstrates how gases of different densities form layers, similar to how air composition varies with altitude.)