You and Your Students!
Vicki Cobb, Education World Science Editor
Make a harmless, spectacular explosion with candy and soda.
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 its like. (If youre curious, Easy Science Projects: Mentos Geyser - Diet Coke Eruption is one such video.) However, Im 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.
One bottle of Diet Coke will give you one geyser. If you want to do this more than once, youll 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.
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!
Heres my event to prove it!
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).
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 youve ever made an ice cream float, youll see lots of bubbles foaming around the nucleation sites on the ice cream. Add sugar or salt to soda and youll 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.
For more on how to squirt liquids check out my book, Squirts and Spurts: Science Fun With Water.
Article By Vicki Cobb
Copyright © 2006 Education World