Background Essay: Acids and Bases: Making a Film Canister Rocket
Two classes of substances well known for combining readily -- and sometimes violently -- are acids and bases. The chemicals that make up these groups vary dramatically, but within the groups they share important traits. Acids are characterized by the fact that they produce positively charged hydrogen ions. Bases, in contrast, produce negatively charged hydroxide ions, composed of one oxygen atom and one hydrogen atom.
When acidic and basic solutions are combined, the acid's positive hydrogen ions and the base's negative hydroxide ions react to form water and release heat energy. The remaining elements combine to form various other compounds, depending on the chemical makeup of the acid and base involved.
Some acid-base reactions produce carbon dioxide (CO2), a gas that is a potentially powerful propellant when under pressure. A vinegar-and-baking soda mixture is just one example that produces CO2. As the CO2 concentration builds up in a closed container, pressure inside that container increases.
In this ZOOM segment, the cast members add vinegar to baking soda, which has been wrapped in some toilet paper. The toilet paper slows the reaction somewhat, giving the cast members time to put the lid on the canister and set their "rocket" upright. The CO2 builds up inside the canister, and the gas eventually forces the canister and attached paper tube to separate from the lid, launching the rocket skyward.