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I love explosions. In my opinion, if you want a kid to get interested in science, explode some stuff. And then explode more stuff. And then make a film canister rocket. And then explode it. Rinse and repeat.
Here is a simple activity to get you started. It is probably best to do this experiment outside, but you can definitely get away with doing it inside on a baking sheet or something to catch the mess. Be sure to stand back a few feet and wear safety glasses. You never know how high the rocket is going to fire!
Safety Concerns: Depending on how much head space you have in your bottle, this can actually cause a pretty violent explosion. The thing to be worried about is getting hit in the eye with the bottle. Be sure to stand back at least a few feet and wear protective eyewear if you have it.
A plastic bottle with a snap top. The little canisters that hold 35 mm film work great, but I couldn’t dig any of those up. I just used a different snap top bottle and it worked fine. (Airborne – how fitting for a rocket! Ha!)
Optional: Thin cardboard to make fins and a nose cone for your rocket. We cut up an old cereal box.
Make the Film Canister Rocket
- If desired, cut out fins and a nose cone for your rocket. Attach it to your bottle with tape or hot glue. (We did tape, and it fell about after 10 or so launches!) Be sure to attach the nose cone on the bottom of the bottle so that the bottom is facing up and the cap-end is facing down at launch time.
- Fill up your bottle with water leaving about 1/2 inch of head space at the top.
- Drop in one Alka-Seltzer tablet and quickly snap the bottle closed.
- Stand back! You’ll see it start to fizz and leak a little bit, then the cap will bulge, then EXPLOSION!
- If one tablet wasn’t enough to make it explode, try it again with two tablets. Or fill the bottle up with more water. Some experimentation may be necessary, but that’s all part of the fun!
- You can always experiment to compare how it works with cold water versus hot water, how it works right side up versus turning the bottle upside down, etc. Record your findings and leave a comment letting me know what you found!
So what makes the explosion happen? It is actually the same chemistry that happens when you mix baking soda and vinegar together. An acid plus a base mix to form carbon dioxide gas, which are the bubbles you see. When enough carbon dioxide has been produced the pressure builds until the container can no longer contain it, at which point the top pops off and the gas and liquid explode out.
Alka-Seltzer is made of citric acid and sodium bicarbonate (baking soda), which acts as a base. When the tablets are solid and dry the acid and base don’t react, but as soon as they are immersed in water they react to form carbon dioxide. This is what causes the explosion. You can even alter this activity just a tiny little bit to make your own lava lamp! (No explosion there, just cool colored bubbles.)
We have done this fun activity a couple of time now. The first time we did it as part of a unit study on volcanoes. I wanted to show the kids that when the pressure builds up under the earth’s crust it can literally blow the top off of a mountain in a volcanic eruption. (This is how Mount St. Helens exploded in 1980.) This video illustrates that explosion very well.