when the dry ice is in the water it occasionally makes a popping sound. how can you explain that?
I expect you are hearing the stress fractures of the dry ice crystals. The same thing happens when you take VERY cold ice cubes from the refrigerator, place them in a glass, then add tap water over the ice. You will hear it pop. Try it.
The popping sound produced when dry ice is placed in water can be explained by the phenomenon of stress fractures. Dry ice is the solid form of carbon dioxide, and its extremely low temperature causes it to be brittle. When dry ice comes into contact with water, the temperature difference can create stress within the solid carbon dioxide, leading to the formation of cracks or fractures.
As the dry ice begins to warm up and sublimate (turn from a solid directly into a gas), the stress within the ice crystals becomes too great and the cracks or fractures suddenly release that stress with a popping sound. This is similar to the popping sound you hear when you place very cold ice cubes into a glass and add tap water over them.
To experience this phenomenon yourself, simply take some dry ice and place it in a container of water. As the dry ice begins to sublimate, you may hear occasional popping sounds as the stress fractures release the built-up stress. Remember to handle dry ice with caution and follow safety guidelines, as it is extremely cold and can cause skin burns.