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Diet Coke Geyser

Starring

You and Your Students!

Directed By

Vicki Cobb, Education World Science Editor

Synopsis

Make a harmless, spectacular explosion with candy and soda.

Genre

• Physical science

Required Props

• Package of Mentos® Mint Candy
• 2 liter bottle of Diet Coke®
• Paper
• Tape
• Index card
• Clear plastic cups, 4-ounce (optional)
• An assortment of sodas -- clear, colored, diet, and non-diet

Setting the Scene

Setting off a Diet Coke geyser has been all the rage on the Internet the past few years. There are videos on the Web that show what it’s like. (If you’re curious, Easy Science Projects: Mentos Geyser - Diet Coke Eruption is one such video.) However, I’m all for doing the real thing -- not just living the fun virtually.

By the way, this Show-Biz Science activity is a lot of fun, but it should be done outside.

Stage Direction

One bottle of Diet Coke will give you one geyser. If you want to do this more than once, you’ll need more supplies. Do this as a demonstration; then follow-up with an activity each student or pair of students can do at their desks.

Show-Biz Science is scripted by popular children's book writer Vicki Cobb. Click to learn more about Vicki or to read a brief synopsis of her philosophy of teaching science. Visit our archive of archive of Show-Biz Science Activities. Watch for a new activity each week. Then chat with Vicki -- share your feedback and ask your questions about teaching science -- on our special Showbiz-Science message board. Be sure to visit Vicki's Kids' Science Page for more great science fun, a complete list of her books, and information about how you can invite Vicki to come to your school!

Plot

Act I
The "trick” behind this activity is to deliver 10 Mentos Mints all at once to a 2-liter, freshly opened bottle of Diet Coke -- then get out of the way!

• Set up your bottle outside on a lawn.
• Roll up a piece of paper to make a tube slightly larger than the diameter of a Mentos Mint candy (about 1 inch in diameter). Tape the tube closed.
• Stack 10 candies inside the tube. (Use an index card to keep the bottom of the tube covered so the candies don’t fall out.)
• Place the tube over the open bottle.
• Slide out the card so all the candies fall into the bottle at once and -- quickly! -- move out of the way. Almost instantly a 15-foot geyser will shoot out of the bottle.

Here’s my event to prove it!

Act II
What really happens when the candy hits the soda? Give each pair of students a clear, 4-ounce plastic cup. Pour about two ounces of freshly opened clear soda (Sprite, for example) into each plastic cup. Have students drop in the candy and watch what happens. Streams of bubbles rise from the surface of the candy. The rate at which the bubbles form is a measure of how well the soda will turn into a geyser. The faster the bubbles come off, the better the geyser. Perhaps your research will reveal a soda that works better than Diet Coke (although regular soda with sugar is a bit stickier).

Behind the Scenes

Carbon dioxide gas is dissolved in soft drinks. Some of this dissolved gas is released when you open the bottle and the pressure on the solution quickly lowers. The release of the dissolved gas is increased with the introduction of a surface that contains "sites” that break up the surface tension of water and allow bubbles to form. In this activity, the surface of the Mentos candy has thousands of such sites, called nucleation sites. Since the candies sink, introducing a lot of candies at once gives the carbon dioxide in the soda lots of places to rapidly form bubbles.

Nucleation sites are not exclusive to Mentos Mints. If you’ve ever made an ice cream float, you’ll see lots of bubbles foaming around the nucleation sites on the ice cream. Add sugar or salt to soda and you’ll see extra bubbles form. The geyser forms because there is a rapid gas build up that forces the liquid out of a relatively small opening.

The End

For more on how to squirt liquids check out my book, Squirts and Spurts: Science Fun With Water.

Article By Vicki Cobb
Education World®
Copyright © 2006 Education World

11/16/2006