Dry Ice Fun - Learning About Dry Ice

Dry Ice Science

Grocery stores use dry ice to keep food cold during shipping. Some grocery stores and ice cream shops will sell dry ice to the public (especially around Halloween) for approximately $1 per pound. Dry ice comes as flat square slabs a few inches thick or as cylinders that are about three inches long and about half an inch thick. Either size will work fine for your dry ice experiments.

Remember the science… dry ice turns from a solid into a gas - a process called sublimation. In other words, the dry ice in the grocery bag will literally vanish in about a day! The experts tell us that dry ice will sublimate (turn from a solid into a gas) at a rate of five to ten pounds every 24 hours in a typical ice chest. It’s best to purchase the dry ice as close to the time you need it as possible. This is the one time when last minute shopping is necessary. If you are planning to perform a number of dry ice demonstrations, plan to purchase 5 to 10 pounds.

Dry Ice Safety

Here’s the background information and safety lesson on dry ice:

Dry ice is frozen carbon dioxide. Under normal atmospheric conditions, carbon dioxide is a gas. Only about 0.035% of our atmosphere is made up of carbon dioxide. Most of the air we breathe is nitrogen (79%) and oxygen (20%). Instead of melting, dry ice turns directly into carbon dioxide gas. It does not melt like real ice. When you drop a piece of dry ice in a bucket of water, the gas that you see is a combination of carbon dioxide and water vapor. So, the gas that you see is actually a cloud of tiny water droplets.

Dry ice must be handled with care as it is -109.3°F (-78.5°C). It must be handled using gloves or tongs, as it will cause severe burns if it comes in contact with your skin. Never put dry ice into your mouth. 

Did you know…

• Dry ice is extremely useful for freezing and keeping things frozen because of its very cold temperature (-109.3°F or -78.5°C). Dry ice is widely used because it is simple to freeze and easy to handle using insulated gloves.
• Dry ice gives more than twice the cooling energy per pound of weight and three times the cooling energy per volume than regular water ice. Dry ice is often mixed with regular ice to save shipping weight and extend the cooling energy of water ice.
• Sometimes dry ice is made on the spot from liquid carbon dioxide. The resulting dry ice snow is packed in the top of a shipping container offering extended cooling without electrical refrigeration equipment and connections.

How is Dry Ice Made?

The first step in making dry ice is to compress carbon dioxide gas until it liquefies, at the same time removing the excess heat. The CO₂ gas will liquefy at a pressure of approximately 870 pounds per square inch at room temperature. Once liquid CO₂ is formed, the CO₂ is sent through an expansion valve and enters a pressure chamber. The pressure change causes the liquid to flash into a solid and causes the temperature to drop quickly. About 46% of the gas will freeze into “dry ice snow.” The rest of the CO₂ gas, 54%, is released into the atmosphere or is recovered to be used again. The dry ice snow is then collected in a chamber where it is compressed into block, pellet, or rice-size pieces using hydraulics.

Can you make your own dry ice? Sure... anything is possible, but it’s not practical (unless you have a huge tank of compressed CO₂ sitting around and lots of extra time on your hands. For $1 a pound, it’s hard to beat the convenience of purchasing it at the store.

Disappearing Ice

Here’s a quick experiment to help children better understand why it’s called dry ice. Ask the children, “Why do you think they call this dry ice?” Place a regular ice cube on one plate and a similar size piece of dry ice on a second plate. Keep both plates out of the reach of the children. “Let’s try to guess what is going to happen to the ice cube and the piece of dry ice if we leave it on the plate for one hour.” Of course, the children are likely to tell you that both pieces of ice will melt, turning into a puddle of water.

Allow the children to view the plates after one hour and to discover the difference between real ice and dry ice. There should be a puddle of water on the plate where the real ice was, but the dry ice plate will be “dry.” Where did the dry ice go? Dry ice is not made from water, it’s made from some of the air that we breathe... it’s frozen carbon dioxide. The dry ice turned into invisible carbon dioxide gas that disappears into the air. Magic... no, it's science!

Burping, Bubbling, Smoking Water

Use the tongs or gloves to place a piece of dry ice in a glass of warm water. Immediately, the dry ice will turn into carbon dioxide gas and water vapor, forming a really cool cloud! This cloud is perfectly safe for the children to touch and feel as long as they do not put their fingers far enough down into the water to accidentally touch the dry ice.

To create the best effect, be sure to use warm water and add a few drops of food coloring to turn boring water into a bubbling potion. Over time, the dry ice will make the water cold and the “smoking” will slow down. Replace the cold water with warm water and you’re back in business!

If you're looking for more fun things to do with dry ice, check out these dry ice activities:

Awesome Dry Ice Experiments

Dry Ice Crystal Ball Bubble

Ghostly Dry Ice Boo Bubbles