A possible explanation.....
Here's the question of the day... Why do Mentos mixed with soda
produce this incredible eruption? You should know that there is
considerable debate over how and why this works. While we offer the
most probable explanations below, we also understand and admit that
other explanation could be possible... and we welcome your
thoughts.
As you probably know, soda pop is basically sugar (or diet
sweetener), flavoring, water and preservatives. The thing that
makes soda bubbly is invisible carbon dioxide gas, which is pumped
into bottles at the bottling factory using tons of pressure. Until
you open the bottle and pour a glass of soda, the gas mostly stays
suspended in the liquid and cannot expand to form more bubbles,
which gases naturally do. But there's more...
If you shake the bottle and then open it, the gas is released from
the protective hold of the water molecules and escapes with a
whoosh, taking some of the soda along with it. What other ways can
you cause the gas to escape? Just drop something into a glass of
soda and notice how bubbles immediately form on the surface of the
object. For example, adding salt to soda causes it to foam up
because thousands of little bubbles form on the surface of each
grain of salt.
Many scientists, including Lee Marek, claim that the Mentos
phenomenon is a physical reaction, not a chemical one. Water
molecules strongly attract each other, linking together to form a
tight mesh around each bubble of carbon dioxide gas in the soda. In
order to form a new bubble, or even to expand a bubble that has
already formed, water molecules must push away from each other. It
takes extra energy to break this "surface tension." In other words,
water "resists" the expansion of bubbles in the soda.
When you drop the Mentos into the soda, the gelatin and gum arabic
from the dissolving candy break the surface tension. This disrupts
the water mesh, so that it takes less work to expand and form new
bubbles. Each Mentos candy has thousands of tiny pits all over the
surface. These tiny pits are called nucleation sites - perfect
places for carbon dioxide bubbles to form. As soon as the Mentos
hit the soda, bubbles form all over the surface of the candy.
Couple this with the fact that the Mentos candies are heavy and
sink to the bottom of the bottle and you've got a double-whammy.
When all this gas is released, it literally pushes all of the
liquid up and out of the bottle in an incredible soda blast. You
can see a similar effect when cooking potatoes or pasta are lowered
into a pot of boiling water. The water will sometimes boil over
because organic materials that leach out of the cooking potatoes or
pasta disrupt the tight mesh of water molecules at the surface of
the water, making it easier for bubbles and foam to form.
When a scoop of ice cream is added to root beer, the "float" foams
over for essentially the same reason. The surface tension of the
root beer is lowered by gums and proteins from the melting ice
cream, and the CO2 bubbles expand and release easily, creating a
beautiful foam on top
Next question... Why should you use diet Coke or diet Pepsi? The
simple answer is that diet soda just works better than regular
soda. Some people speculate that it has something to do with the
artifical sweetner, but the verdict is still out. More importantly,
diet soda does not leave a sticky mess to have to clean up. Hey,
that's important.
What's the record for the biggest Mentos fountain? My official
record is a 18 foot blast that shot up and almost took out a half
million dollar, high-definition television camera. You'll find
video on-line at www.SteveSpanglerScience.com of some of our
favorite eruptions.
On a personal note... I've performed this demonstration well over a
thousand times - on television, talk shows, science conventions,
teacher associations, for CEO's at huge motivational speaking
rallies, for Nobel Prize winners and anyone else who might watch.
And the reaction is always the same... that's amazing! My thanks to
Lee Marek who originally shared the Mentos idea with me and to the
hundreds of teachers and science enthusiasts who continue to share
their funny pictures, videos and experiences.
