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Make a Smoking Bubble “Bomb”
In this science experiment, kids observe a large carbon dioxide bubble made by dry ice "melting" into a gas; the bubble then pops with an awesome smokey finish.
Dry ice is frozen carbon dioxide. Carbon dioxide is the same gas that we humans breathe out; it is all around you. As frozen carbon dioxide warms, it goes from being a solid to being a gas without ever becoming a liquid; this is called sublimation. When a cube of dry ice is added to water, it "melts" into gas that bubbles to the top. When the bubbles pop, the carbon dioxide gas coming out sinks down instead of floating up into the air because it is heavier than air.
We added soap so that the bubbles would last longer and form into a mound.
Safety Notes
Dry ice is dangerous and should only be handled by an adult. If touched, it can cause burns. If enclosed in an air-tight container, it can also cause the container to pop open unexpectedly. Always keep children out of reach of the dry ice, always use tongs or thick leather gloves when moving the dry ice, always store it in a container with ventilation, and never attempt to chop or break it in a way that bits could fly up into someone’s face or eyes.
Materials
- dry ice - 1 tablespoon per student
- disposable cup with plastic lid - 1 of this item per student
- water - 1 cup per student
- bubble solution - 1/2 cup per student
- bowl - 1 of this item per student
Instructions
Find a plastic cup with a matching lid. Any cup from a fast food restaurant or smoothie place will work great, though a clear cup is more fun because you can watch the dry ice sublimate.
Carefully cut out the center of the plastic lid. You want this to be as large, smooth and circular as possible while leaving the outer ring intact. This may require some grownup assistance.
Fill the matching disposable cup about halfway with water.
GROWNUPS: Add a small cube of dry ice to the cup of water. (Please see safety warnings.) The dry ice will begin to sublimate immediately.
KIDS: Pour bubble solution into the bottom of a bowl. Dip the plastic ring you made from the lid into the bubble solution. When dipping, make sure the lid is upside down (the edges should be curling up toward you.) A film of bubble solution should attach across the opening, just like it would on a regular bubble wand.
Carefully flip the lid over and set it on top of the cup with the dry ice. The gas escaping from the "melting" dry ice will push out against the bubble film and cause a large bubble to form. The bubble will eventually burst; when it does, the gas will come crashing down all around the cup!
Extensions & Troubleshooting:
Try using the lid to transfer the bubble film to the top of the cup itself, then removing the lid. We found this made an even bigger bubble!
If you are getting lots of little bubbles instead of one big one, it likely means you've got bubble solution down in the water in the cup. If this happens, empty and wash the cup, then replace the water and dry ice and try again.
This may seem like it's too complicated for younger scientists, but we've found they love it. Even if they can't form a perfect bubble, they enjoy trying!
