Three Rockets for Launch Day
1Every spring, the Hilltop Middle School Rocket Club hosts a launch day for younger students. The club leader, Ms. Greta Ndiaye, launches the model rockets that have real motors. The club also builds three small demonstration rockets that use no fire. Club members Pilar Haugen and Rashid Coelho wanted to find out which of the three demonstration rockets works because of a chemical reaction.
2The bottle rocket is a plastic bottle partly filled with tap water. An adult pumps air into it to a safe pressure and then releases it, and the air pushes the water out of the bottom as the bottle shoots up. At the moment of launch, a white fog fills the bottle and is gone within a few seconds. When a gas expands quickly, it cools, and some of the water vapor in cooled air can condense into tiny droplets.
3The canister rocket is a small plastic canister with a snap-on lid. Rashid drops in half of a fizzing tablet, adds a spoonful of water, snaps on the lid and stands the canister upside down. The tablet is citric acid and baking soda pressed together. Within about 10 seconds, the lid pops off and the canister jumps a few meters into the air. Everyone nearby wears safety goggles.
4The balloon rocket rides along a string. Wearing insulated gloves, Ms. Ndiaye drops pellets of dry ice into an open flask and stretches a balloon over its mouth. When the balloon fills, she pinches it shut, slips it off and tapes it to a straw on the string. Dry ice is very cold, with a density of 1.56 g/cm³, and it turns straight into a gas without melting.
5After launch day, Ms. Ndiaye and the high school chemistry teacher collected the gas from each rocket in bags and measured two properties of each gas. They also let the liquid left in the canisters dry in a dish and tested the white powder left behind, along with the tablet's two ingredients.