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Soda Water Fountain Experiment #335
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By: Robert Krampf

The name for this week's experiment comes from the song "Big, Rock Candy Mountain", which was a favorite of mine when I was young. The experiment was the result of an accident. I was picking up a large bottle of soda and almost dropped it. As I grabbed it, it hit the corner of a cabinet, which made a small hole in the side. A spray of soda jetted out, making a direct hit on our cat. Rushing to the sink, I managed to spray the window, the stove, the cabinets, my wife, the clean dishes, a shelf of cookbooks, etc. It is all cleaned up now, and everyone has forgiven me, except for the cat. I am sure she has a surprise planned for me at about 3 AM. You can try this in an even more dramatic way, with less cleanup, through a process called nucleation.


You will need:

a 2 liter bottle of carbonated soda. Cheap, off brands work just as well as the big names.
a screw-on cap from another bottle of soda
a roll of peppermint Lifesaver candies, or other mints with holes.
a nail
a candle or lighter


This experiment uses fire, so be sure to have an adult around, so you have someone to blame if something goes wrong. Be safe and think about things before you do them.

The first thing you need to do is make a small hole in the extra bottle cap. I did this by holding a nail with the pliers and heating the point. I then used the hot nail to melt a hole in the center of the cap. Have a glass of water handy, to drop the hot nail into when you are done.

Take a piece of thread and tie one end of it to one of the mints. String 3 or 4 more mints onto the thread, like beads on a necklace. Stick the other end of the thread up through the hold in the bottle cap. Pull the thread to hold the mints firmly against the inside of the cap. Use a piece of tape across the top to hold the thread in place.

Take the cap with the mints and a bottle of soda outside. Find an area where there is nothing that will be harmed by a spray of soda. Be sure there are no cars, windows, flower beds, etc., around. Be especially sure there are not cats nearby.

Place the bottle of soda on the ground. Remove the cap, and carefully put the cap with the mints on instead. The mints should fit inside the bottle and be above the soda. Screw the cap on tightly. Hold the thread and carefully remove the tape. Get ready to run. Release the thread and move back quickly. When the mints fall into the soda, a jet of liquid will shoot up about 20 feet in the air. The spray will continue for several seconds.

Why did it do that? The fizz of a carbonated soda is a gas called carbon dioxide. This gas is dissolved in the liquid, but it does not stay that way. When you pour some soda into a glass of ice, you will see quite a bit of the gas being released as bubbles and foam. The rough surface of the ice traps tiny bubbles of air. These tiny bubbles collect more gas, growing into larger bubbles.

A similar thing happens when you shake a bottle of soda. You are putting lots of tiny bubbles into the liquid. These bubbles serve as a nucleus or starting point, for more gas to collect, producing the foam. That is what happened when I dropped the bottle. If it had not been punctured, then the tiny bubbles would have risen to the surface and popped. Once the tiny bubbles are gone, you no longer get the burst of foam when you open the bottle. Tapping the top of can of soda helps bring these bubbles to the surface, keeping the
can from producing lots of foam when you open it.

When we dropped the mints into the soda, the rough surface of the mint trapped air, producing thousands of tiny bubbles for nucleation sites. Since there is a small hole in the cap, the foam has a place to escape. The force of the escaping gas squirts the liquid quite a way up into the air.

After your fountain stops, point the bottle away from you (not towards your cat!) and give it a shake. You will probably not get much reaction, as most of the gas has escaped. That is why we used a cheap brand, as the soda that is left will be flat and not very tasty.

Another way to demonstrate nucleation is by adding a scoop of ice cream to the soda. This produces very tasty foam, and a wonderful snack at the same time. There may be some variations with different sodas and flavors of ice cream, so I suggest you try several different combinations.

From Robert Krampf's Science Education Company

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