Materials:

• Self-seal Baggies
• Dry Ice
• Ammonia
• Water
• Dirt
• Light Corn Syrup or Vegetable Oil
• Cooler for dry ice
• Tablespoons and Measuring Cups
• Safety Goggles
• Wet Wipes
• Oven Mitts
• Plastic Floor Covering

Instructions:

1. Using oven mitts put about 1/4 cup of dry ice in a re-sealable bag. (Dry ice is available from a dry ice or carbon dioxide sales company. Do not handle this with bare hands as it is extremely cold, approximately -76 degrees F.)
2. Add about 1/4 cup ammonia-water mixture (1 capful of ordinary household ammonia in one cup of water). This mixture will bubble and a “tail” will form as the dry ice heats up.
3. Then add about one tablespoon of light corn syrup, vegetable oil, or colored water and a spoonful of dirt. Seal bag and shake gently.
4. Place the bag on the plastic floor covering. Do not hold the bag after it has been shaken. The gases will expand until the bag pops - the bag will not burst unless you have shaken it too hard.
5. The comet turns directly from a solid to a gas, which is what comets do in space when they are heated by the sun. This is called sublimation. The “tail” is gaseous carbon dioxide escaping through small holes in the frozen water. After a while, the comet will become a crater-filled ice ball as the volatile carbon dioxide sublimates.

Science:

Why does the bag pop?

A build up of carbon dioxide gas is caused as the dry ice mixture sublimates from solid to gas. (Sublimation is the process of turning a solid into a vapor or gas upon heating, which is what the dry ice is actually doing.) The water represents the water present in a comet. The ammonia represents methane and other simple liquids and gases found in comets. The corn syrup, vegetable oil, or colored water represents the compounds that contain hydrogen and carbon that are found in comets. The dirt and sand represent the carbon, dirt, and dust that are found in comets. Comets are different from one another which is why some split up and others hold together.