Keep Cool with Dry Ice
Chance are that you enjoyed your Independence Day holiday in a hot place. Temperatures soared around the world last week, breaking records from Ireland to Iowa. We know that sometimes it feels even hotter than the air temperature indicates. That’s where the heat index comes in. The heat index factors in the impact of relative humidity to indicate how hot it feels. (Wondering what the heat index is in your area? There’s an app for that.)
Cool Stuff for Hot Times
All this heat has me thinking about something cool--dry ice. Now, thinking cold thoughts doesn’t make a day with a heat index of 110 Fahrenheit feel any more pleasant. But doing a few experiments with dry ice can provide a pleasant distraction.
Dry ice is a solid, frozen form of carbon dioxide. Unlike the ice cubes in our freezers, which melt in the traditional paradigm of solid to liquid, dry ice sublimates. That is, the CO2 turns directly from a solid into a gas at room temperature.
Handle with Care
With a surface temperature of -109.3 degrees Fahrenheit (-78.5 C) dry ice can cause frostbite to your skin. So handle it, like all chemicals in the lab, with caution. Wear insulated gloves and safety glasses, even if your “experiments” only involve curious, playful exploration.
You may find dry ice at your local grocery store, although you may have to special order it. I have found that there are typically a few local ice cream parlors that sell it by the pound. A $5-$10 budget should buy you more than enough dry ice for your experimental needs.
Don’t be too proactive, though. Dry ice continues to sublimate even if you wrap it tightly in newsprint and store it in your freezer or a cooler. If you buy it more than a day ahead of time, it might be gone by the time you try to use it. I speak from experience when I say that solving the Mysterious Disappearance of the Dry Ice is much less fun than experimenting with it.
Just Add Water
Watching dry ice sublimate is interesting, but the real fun begins when you add water. Fill a medium plastic bowl with about a quarter cup of water. While the dry ice is still wrapped up, take a hammer (remember those safety glasses) and break it into pieces. Using a gloved hand or tongs, place a piece of dry ice into the water and watch sublimated gas bubble up through the water. Feeling like a mad scientist? Then experiment! What is the effect of adding water by the drop compared to pouring a large quantity on the ice? Swap your bowl for differently sized and shaped containers to find the formula for maximum drama.
Good, Clean Fun
Take a classic summer activity, blowing soap bubbles, and add dry ice. There’s no need to blow. Simply add dish soap to your water and dry ice combo and let science do the work for you. When the foggy bubbles pop, they release a small cloud of carbon dioxide. It’s exciting to watch, but if you want to shape your own bubbles, soak a string or a piece of yarn in your bubbly cauldron and then run it around the upper edge of the bowl to seal it with a soapy layer. The dry ice will sublimate into that layer to form a large cloudy bubble. Try it at night and then add the contents of an activated glow stick to your solution for even more fun.
Fight Fire with...Dry Ice
Flames are fueled by oxygen. Dry ice sublimates into carbon dioxide. So what happens if you place a candle in a jar, light the candle, and then add dry ice?
The Screeching Spoon
Place a chunk of dry ice into a plastic sandwich-sized container. Run a metal spoon under very warm water and then shake it dry. With a gloved hand, press the spoon up against the piece of ice. The warm spoon and pressure speed up the sublimation process. The increased CO2 release pushes up against the spoon and lifts the spoon off the ice slightly. But the pressure you are applying pushes the spoon back down into the ice. Although this process might be difficult to observe with your eyes, your ears will know it’s happening because the vibrating metal will create a screeching noise.
I hope you have as much fun exploring and experimenting with dry ice as my kids and I do. And when you're done, go back to your boring summer!