Dry Ice in a Balloon

Description

Solid dry ice is placed in a balloon. It sublimes, and the resulting gas occupies a much larger volume than the solid; the balloon expands greatly, and often bursts. When a balloon is filled with a gas more dense than air, the balloon may serve as a lens focussing sound and giving the effect of amplifying the sound. Speaking through the balloon to the class demonstrates this effect.

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Improper handling of dry ice can lead to burns. Exploding balloons can send debris into eyes.

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• Handle the dry ice cautiously. Do not touch with bare fingers; wear gloves, or wrap in a towel.
• Wear eye protection when working with the balloon.

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1. Dry ice is usually produced in cubes about 25 cm on an edge. When you purchase some dry ice, the dealer will use a band saw to cut the ice to a rectangular block of the desired weight and will usually give it to you wrapped in paper. The block will be fragile. Break the block into large pieces in its paper wrapper. Transfer to a small styrofoam chest.
2. Wear a glove. Remove the desired amount to the center of an old bath towel or piece of canvas. Wrap the ice. Smash it against the floor until the dry ice breaks into a powder.
3. Use a powder funnel and a scoopula to place about 25-50 mL of dry ice in a giant balloon. Knot the top. Note the surface of the balloon.
4. Set the balloon aside. Note changes with time.
5. Demonstrate the effect of speaking through a balloon filled with carbon dioxide.

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Name ___________________________ Class ________

Teacher__________________________

DoChem 087 Dry Ice in a Balloon

Watch the movie.

What effect does the nature of the gas have on the ability of a balloon filled with that gas to transmit sound?

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Purpose

• To demonstrate the relative volumes of the solid and gaseous states of matter.
• To demonstrate the sound transmission qualities of a balloon filled with carbon dioxide.

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• cooler, gloves, mallet, towel, hot pads
• dry ice
• balloon
• powder funnel
• scoopula

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• Dry ice is needed for this experiment. The expansion of gaseous carbon dioxide under high pressure will produce dry ice as a result of cooling upon expansion. This is inefficient and expensive. Ice companies often sell dry ice for reasonable prices.
• A Mylar^® balloon also may be used; it will not break easily.

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Teacher preparation (assuming dry ice handy): 10 minutes

Presentation: 10-50 minutes

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• Allow unused dry ice to sublime. (Plan several experiments using dry ice on the same day; floating a bubble, carbon dioxide as an acid, etc.)
• All other materials may be saved or disposed of with ordinary trash.

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Presentation Question:

• What effect does the nature of the gas have on the ability of a balloon filled with that gas to transmit sound?
  • The balloon acts as a lens. The balloon should be large compared to the wavelength of the sound -- a larger balloon than shown works better. When the filling gas is more dense than air, the balloon behaves as a convex lens and concentrates the sound. The balloon-lens foci can be found, for example. A gas less dense than air is expected to disperse the sound.

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• gas
• dry ice
• sublimination
• volume
• expansion

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