Use dry ice to make frozen bubbles that display beautiful frost patterns. You can pick up the solid bubbles and examine them closely to learn about density, sublimation, diffusion, interference, and semipermeability.
Frozen Bubble Materials
- Dry ice
- Bubble solution (buy it or make your own)
- Deep container
A deep glass mixing bowl is perfect for this project because it’s easy to observe the dry ice and bubbles. But, you can use any bowl or pot or even a cardboard box.
Freeze Bubbles With Dry Ice
- Use tongs or wear gloves to place some dry ice into a container.
- Allow about 5 minutes for the dry ice to sublimate into carbon dioxide vapor. The resulting fog is a combination of carbon dioxide and condensing water vapor.
- Blow bubbles into the container. Gravity draws the bubbles down, but once they reach the carbon dioxide layer they hover. Eventually, the bubbles fall toward the dry ice. As the bubbles chill, they freeze.
- Pick up frozen bubbles to examine them. You don’t need to use gloves to handle the bubbles, but they’ll last longer if you pick them up with a bubble wand.
- Watch the bubbles change as they age. Frozen bubbles become transparent and develop bands of color as they melt. Gravity pulls the bubble solution downward, eventually thinning the film at the top of the bubble until it pops.
How It Works
Dry ice is the solid form of carbon dioxide (CO2). Solid carbon dioxide doesn’t melt into a liquid, except at high pressures. Instead, it undergoes sublimation, changing from a solid directly into a gas. The carbon dioxide gas is colder and heavier than air (mostly nitrogen and oxygen), so most of it settles to the bottom of the bowl. Eventually, diffusion mixes the carbon dioxide with air, but it forms an invisible layer for several minutes.
When you blow bubbles, you fill them with air. Your breath is slightly enriched with carbon dioxide, but it’s still much less dense than the cold vapor in the bowl. So, bubbles float on the dry ice layer.
The extreme cold above the dry ice freezes the water in bubble solution. Frost patterns form as the water crystallizes. But, the bubble shell is very thin. It is semipermeable to gases, so carbon dioxide enters the bubble. This increases the gas density inside the bubble, causing it to sink.
If you shine a light on the soap bubble, you’ll see a rainbow of colors. This is an interference pattern, caused by slight differences in bubble thickness. Thickness differences bend light differently, forming colors.
Safety
Dry ice cold enough to cause frostbite (−78.5 °C or −109.2 °F), so wear gloves or else handle it with tongs. As dry ice sublimates, the cold carbon dioxide sinks to the floor before mixing with air. Working with a small amount of dry ice poses no significant risks, but it’s best to work in a well-ventilated area. High carbon dioxide concentrations from vaporizing a lot of dry ice presents a health hazard, especially to children and pets, because they are not as tall.
Other Fun Projects
Use leftover dry ice for other fun science projects, such as making fog, a “crystal ball,” a simulated comet, and carbonated ice cream. If you don’t have dry ice, you can still freeze bubbles with frost patterns, but you’ll need very cold temperatures.