Film Canister Alka-seltzer Rockets
[Shopping List: film canisters; alka-seltzer; water; buckets]
- Fill the film canister half full of water.
- Have the kid practice putting on the lid – they will need to put it on quickly after adding the alka-seltzer.
- Give each kid a quarter of a tablet of alka-seltzer. Have them drop it in the canister, put on the lid, shake it a few times to start the reaction, and place it upside down in an area a few feet away from people.
- Wait for the reaction! It may take 30-45 seconds, so don't get impatient and retrieve the rocket in the belief that it is defective.
What's Happening: Alka-seltzer tablets contain citric acid and sodium bicarbonate: an acid and base pair. In the dry tablet, these two compounds don't mix or react with one another. Once dropped into water, however, the acid and base dissolve and come into contact with each other, producing an acid-base neutralization reaction which creates carbon dioxide gas and sodium citrate (H3C6H5O7(aq) + 3 NaHCO3(s) 3 CO2(g) + 3 H2O(l) + NaC6H5O7(aq)). Because the reaction will continue until it has reached equilibrium, the gas builds up inside the canister until enough pressure has been generated to force off the lid. Because the rocket is sitting upside down, the lid is forced down and the rocket is launched into the air due to Newton's 3rd Law (for every action there is an equal and opposite reaction).
Variations: Try switching between hot and cold water – does this affect the height of the rocket? What about more or less Alka-seltzer?
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