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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.
Materials:
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.
thread
tape
a nail
pliers
a candle or lighter
Plan: 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 To start receiving the Experiment of the Week, just send a blank E-mail to: krampf-subscribe@topica.com | 
