Posted by: Discovery Science Center Blog | June 30, 2010

Make your own Rocket at Home!

Make Your Own Rocket!

Materials:

Towels

Fuji Film Canisters with inverted lids

Seltzer tablets

Water

Cookie Sheet

Discussion

Make your own seltzer tablet rockets which demonstrate the results of a chemical reaction.  If you look at the ingredient list of Alka-seltzer, you will see it is made primarily from baking soda (sodium bicarbonate) and citric acid.  When dealing with acids and bases on the pH scale, you may notice that these two ingredients are the opposite of one another: baking soda is a base and citric acid is, of course, an acid.

When you drop the tablet in water, this enables a chemical reaction (very similar to when you mix baking soda and vinegar to create a model volcano). The dry chemicals are released into the water where they can chemically react with one another.  You can see the tablet start to break apart and fizz.  The fizzing is the production of gas bubbles  ~ the production of gas is evidence of a chemical reaction.  In this experiment, the gas produced is carbon dioxide (CO2).

The carbon dioxide in this reaction helps reduce the amount of stomach acid, relieving acid indigestion and heartburn (which is really esophagus burn since the stomach acid can work its way up into the esophagus).  There is also aspirin in the Alka-seltzer which can help relieve the pain produced by too much acid in the digestive system.

We are going to use this chemical reaction as energy to power our film canister rockets.

Guidelines

Fill  film containers about 1/3 of the way full of water.   On the count of three,  break piece of tablet in half, drop broken tablet pieces into the container, make sure they give the container a quick shake, then place the container lid-side down onto the cookie sheet.  Explain how important it is that the students then sit back and not hover over the cookie sheet ~ the force of the blast-off can do real harm.

What is happening

As the Alka-Seltzer tablet dissolves, it releases carbon dioxide, filling the film canister to the bursting point  ~ increasing the air pressure inside the canister.  The lid pops off as the gas rushes outward; this outward rushing air pushes the film canister upward ~ a great example of Newton’s Third Law:  “For every action, there is an equal and opposite reaction.”

If you imagine yourself swimming in a pool and pushing off of the side to begin your swim ~ you have an idea of how the gas molecules push off of the end of the film canister on their way to rush out of the opening of the canister.  (The amount of force you have to use to push yourself off the side of the pool is equal to the amount of force required to get you a particular distance in the pool ~ your feet are pushing backwards while your body is moving forward in the opposite direction.)

Now think of you as the film canister and the side of the pool as the cookie sheet.  Since the film canister is not heavy, it responds by pushing off of (away from) the gas, thereby moving in the opposite direction of the escaping gas.  So the force hitting the cookie sheet as the gas rushes out is equal to the force that propels the film canister upward: “For every action, there is an equal and opposite reaction.”  (Use your hands starting palm-to-palm and moving away from each other to show equal forces moving in opposite directions.)

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