Tuesday, July 03, 2007

Why does putting Mentos into a bottle of diet Pepsi cause an explosion?

Who's asking: James Lamb, Virginia Beach, VA

Today's deliberately silly post is willful denial of many bad things that have happened in the last couple of days, and are happening even as I type this. In a rotten world -- a world where leaders are cowards, doctors are terrorists, good people get sick and Beverly Sills is dead -- you can still put a handful of Mentos into a bottle of soda and make magic. Do try this at home. And get well soon, Mary.

Okay, you're asking, why is this Independence Day-related? Because it is a great American tradition to blow stuff up on the 4th of July, and this is a safe way to do it, with no risk of anyone losing a finger or anything catching fire.

If you haven't seen it, go watch the phenomenon here. (The video's a little long, but it's funny and makes an important point: you must use original Mentos mints, the white ones. Mentos gum doesn't work.)

Anyway, how it works is that you open a two-liter bottle of Diet Pepsi, and with a paper funnel, pour in a handful of Mentos mints (I have had the best results with five). Step back and watch the soda shoot into the sky in a spectacular fountain. Theoretically, this will work with any type of soda -- but I've never tried it with sugared soda, because it would get too sticky, and Diet Coke did not produce as big a geyser as Diet Pepsi.

So what makes this happen? Theories abound, but no one knows for sure. In fact, scientists don't agree on whether it's a physical reaction or a chemical one. The theory that makes the most sense to me (an educated layperson) is that the surface of original Mentos are covered with microscopic pits that form "nucleation sites" for carbon dioxide to form bubbles. Dropping Mentos into the soda creates so many bubbles that the gas forces the liquid out of the bottle, and it all goes straight up. (The liquid left in the bottle is flat.) The phenomenon works with bottles smaller than two liters, but the two-liter bottle seems to provide the right amount of air to maximize pressure within the bottle.

James asks the obvious follow-up question, which is whether eating Mentos and drinking Diet Pepsi will cause a similar eruption in your own stomach. The answer to that is no. You chew Mentos before you swallow them, which breaks up the surface tension (getting rid of those nucleation sites) and mixes the Mentos with your own digestive acids. The acids in your stomach break down the carbon dioxide in the soda, too, so there's never an opportunity for the chemical or physical reaction to occur.

That said, I wouldn't pop a handful of Mentos and then swig a Diet Pepsi. I just wouldn't.


Linda Brown said...

What if you swallowed the Mentos whole and then drank the soda?

Or held them in your mouth and took a swig of Diet Pepsi?

Didn't you ever do Pop Rocks?

No fireworks in the L.A. area this year -- too dry. Should have stayed in Missouri -- there were fireworks stands all over the place when we were there last weekend. And they've had a lot of rain recently, so there's little fear of fire.


AnswerGirl said...

Not even off the Santa Monica pier? Bummer.

Linda, feel free to make those experiments if you want. Let me know how things turn out...

Anonymous said...

One should use care when discussing this phenomenon with teenagers. I caught my daughter a fraction of a second before she dropped a Mentos in a Diet Coke… in the kitchen. The ensuing eruption would have been minor compared to my wife’s reaction had this actually occurred. Mothers have little sense of humor. For my favorite Mentos/ Diet Coke video check out this one at YouTube. It’s like Mentos at the Bellagio.


On the subject of fireworks and dry weather, three boys just set fire to their school in suburban St. Louis resulting in $1 million in damages. Dang it!

Happy 4th!

St. Louis

Anonymous said...

Would you drink a diet pepsi at 6:44 in the morning?

You meant to mention that the two guys on Youtube doing the Mentos in DP were from Maine


Anonymous said...

I meant the two guys who did geysers with Diet Coke to in the kenetic art video


AnswerGirl said...

I would not ordinarily drink a Diet Pepsi at 6:44 in the morning, but I'm sure I have, at some point -- desperate times, desperate measures.

Of course I should have mentioned the Maine connection... thanks, Richard!

Anonymous said...

And I meant to write the second post in English


Diane said...

The Mythbusters took on this particular challenge. Here is the address to an article about the experiment which has another link to the video from their show. Enjoy!!http://www.zap2it.com/tv/news/zap-mythbustersmentos,0,4325641.story

AnswerGirl said...

Cool -- thanks, Diane!

Now I have to go try this with table salt...

Diane said...

Actually, the video is missing, now. Hmmm...Anyhoo, here's another address for the same episode.