SAFETY NOTE:
NEVER PLACE dry ice into a closed container such as a soda bottle. The bottle can explode with a loud bang, damaging your eardrums. Loose plastic, such as the bottle cap, may fly off, damaging someone’s eyes. THIS HAS HAPPENED! click for news story. DON’T DO IT!
What’s Dry Ice?
Dry ice is frozen Carbon Dioxide, or CO2, which is a gas under standard temperature and pressure conditions. The atmosphere contains about .035% of this gas. CO2 is a greenhouse gas, which means it absorbs light at infrared wavelengths. An increase in the concentration of this gas would, some scientists believe, cause an increase in the atmosphere’s average temperature. The high concentration of CO2 in the atmosphere of the planet Venus is said to contribute to that planet’s high average temperature.
At normal atmospheric pressure on this planet, frozen CO2 doesn’t melt into a liquid, but rather evaporates directly into its gaseous form. Hence the name dry ice. This process is called sublimation. All of the experiments below rely on this property of dry ice.
Getting Dry Ice
Dry ice is commonly available from ice dealers in two forms: flat square slabs a few inches thick and about eight inches on a side; or cylinders about half an inch in diameter and from a half to 2 ½ inches long. The price for ten pounds is around six dollars. If you buy less than this you will pay about a dollar per pound.
Storing and Transporting Dry Ice
Dry ice continuously sublimates as heat enters it from its surroundings. The CO2 gas that evolves must be vented from the container. Do not seal dry ice into a container except as detailed below, because an explosive bursting of the container can result. A Styrofoam (polystyrene foam) ice chest with a loose fitting lid makes a good container for transporting dry ice.
Handling Dry Ice
Due to its extremely cold temperature (-78.5oC, or -109.3oF), dry ice can cause damage to the skin if handled. Use tongs or insulating gloves when handling dry ice. It is also important when crushing or grinding the solid not to get any of the dust into your eyes. Wear protective goggles.
Popping Film Cans
A fun (and often wild) activity vividly demonstrates the sublimation process. Place a piece of dry ice into a plastic 35mm film container - the kind that has the snap - on cap. Then wait. The cap will pop off, and sometimes fly several meters. The clear Fuji brand containers shoot farther than the gray and black Kodak type. Warn anyone performing this experiment not to aim for anyone’s eyes.
Inflate A Balloon
Grab an uninflated balloon and force the neck open with the index and middle fingers of both hands, stretching the balloon open. This will allow you to drop in one or more pellets of dry ice. Tie the balloon closed. Set aside, and observe for awhile. Better yet, drop the balloon into a pond or swimming pool. This will help supply heat to the dry ice. At first, the balloon will sink, but soon, as it begins to inflate, it will rise to the surface.
If you manage to put enough dry ice into the balloon, it will eventually reach the bursting point. Again, this is lots of fun if the balloon is in a pool.
Sound Lens Using a Balloon
A balloon full of CO2 gas can act as a sound lens, because sound travels more slowly in CO2 than it does in air, Just as light travels more slowly in glass than in air or vacuum. Do not use a balloon for this if it is over - inflated, or if it contains remaining pieces of dry ice, because the balloon could burst, causing temporary or even permanent deafness. Hold the balloon about a foot from your ear, and listen for faint sounds, such as a radio turned low, a ticking clock or a distant conversation, to appear louder.
Hero’s Engine
Using a push pin, or a straight pin held in pliers, poke two holes into opposite sides of a film can, near the bottom. The holes should be off - center, like pinwheel rockets. Tie a loop in a length of thread. The loop should fit loosely over the cap of the film can, so that when you loop it over the cap, and snap the cap onto the can, you can hold the can by the remaining length of thread. Place a small piece of dry ice into the can. Then quickly add some warm water, and close the lid, with the thread attached. Lift the can by the thread, and watch what happens.
Singing Spoon
Press a warm spoon firmly against a chunk of dry ice. The spoon will scream loudly as the heat of the spoon causes the dry ice to instantly turn to gas where the two make contact. The pressure of this gas pushes the spoon away from the dry ice, and without contact, the dry ice stops sublimating. The spoon falls back into contact again, and the cycle repeats. This all happens so quickly that the spoon vibrates, causing the singing sound you hear.
Fog Effects
When you place dry ice into some warm or hot water, clouds of white fog are created. This white fog is not the CO2 gas, but rather it is condensed water vapor, mixed in with the invisible CO2. The extreme cold causes the water vapor to condense into clouds. The fog is heavy, being carried by the CO2, and will settle to the bottom of a container, and can be poured. You can produce enough ground - hugging fog to fill a medium sized room with a pound or so of dry ice. Do not allow anyone to lay down in this fog, or allow babies or pets into it, as CO2 gas does not support life. Dry ice fog allows low powered laser beams to be seen; see the laser experiments page for details.
Carbonation
Dry ice, being frozen CO2 gas, can be used to carbonate water to create sparkling water. Place some drinking water in a glass, and add some dry ice. Allow it to bubble. Water ice may form around the dry ice. If this happens you can either leave it alone, or break it up with a spoon to help the process along. When all of the dry ice is gone, taste the water that remains. It should taste slightly carbonated.
I haven’t tried to see what happens when you do this in a closed container, as I haven’t yet determined what is a safe quantity of dry ice to add, that will carbonate the water yet not burst the container. See safety note above. So I would strongly caution you against doing this, unless you take the proper safety precautions, such as providing a secondary container ( a coffee can perhaps?) to catch any projected pieces of plastic soda bottle. Also, cover your ears or use earplugs, just in case the container bursts. Don’t do the experiment in a glass container!