Dry ice is solid Carbon Dioxide, so when it thaws, it produces Carbon Dioxide gas. Carbon Dioxide is heavier than air, and the heavy gas will stay in the fish tank or Wok.
The bubbles are filled with air, which is "lighter" than Carbon Dioxide. So they will float on the carbon dioxide.
Sometimes, a bubble will fall through the bubble solution and onto the dry ice. Then the bubble might freeze in place, and sometimes it will freeze while it is in the middle of popping!
Osmosis and bubbles
If you’re lucky, one of the bubbles will come to rest on top of the layer of Carbon Dioxide. If so, watch the bubble closely, as it will slowly start to grow.
It is growing by a process similar to osmosis, which is how water enters and leaves your cells. The bubble membrane is permeable to Carbon Dioxide. As the bubble sits on the layer of gas, Carbon Dioxide slowly seeps into the bubble making it grow larger.
Eventually, the bubble may become so filled with Carbon Dioxide that it either pops or starts to fall into the dense gas layer, where it can freeze.
Bubbles, bubbles, and more bubbles
A lot of people love mixing baking soda and vinegar to make Carbon Dioxide bubbles.
Try doing the same activity by using baking soda and vinegar (instead of dry ice) to make Carbon Dioxide.
Does it work as well?
Can you create a fun science fair project comparing how well bubbles float on Carbon Dioxide from the two different sources?
Great Demo: Dry Ice a fire extinguisher
Carbon dioxide is denser than the air, so it can be used as a fire extinguisher.