It’s time once again for a fun home activity. Last time I talked about how to make ice cream at home with some dry ice and a few simple ingredients. Today I’d like to do something we did at our recent Taste of Camp Quest NorthWest picnic, the ever-popular Diet Coke and Mentos reaction. It’s very easy to do this at home, so grab some 2 liter bottles of Diet Coke and a couple packages of Mentos and give it a try.
What you’ll need:
2 liter bottles of Diet Coke (other sodas will usually do as well, but Diet Coke seems to have the best reaction and doesn’t leave a sticky mess)
Mentos, enough for between 1 and 8 candies per bottle of soda.
First, a warning: While the combination of Diet Coke and Mentos is generally safe, it is possible to get hurt with it if you aren’t careful. Please limit the reaction to the 2 liter bottle, don’t be tempted to ingest the ingredients as you might get a severe stomach ache. Also, be sure to stay clear of the top of the bottle when you drop the Mentos in. If nothing else, you don’t want a face full of Diet Coke.
Before getting to the experiment, let’s go over the science of what we’ll be seeing. Why is soda bubbly? As you probably already know it’s due to carbon dioxide (CO2) gas. Until a bottle is opened the gas is (mostly) suspended in the liquid and isn’t released. Soda makers inject more CO2 into the water than would normally dissolve under natural conditions. When you open the bottle the CO2 in the water will try to escape, bringing it back to a more natural state. When you shake a can or bottle of soda water it agitates the CO2, allowing it to more easily combine and break free of the water. When you open the bottle these bubbles can escape, reducing the pressure which in turn allows the bubbles to increase in volume following Boyle’s law, which states that at a fixed temperature pressure and volume are inversely proportional. In other words, when one doubles the other halves. So as the pressure drops the volume of the gas will increase.
Water molecules are strongly attracted to one another. In order to form a new bubble, or expand an existing one, the water molecules must push away from each other. This surface tension requires extra energy to break. When you add Mentos to the soda the gelatin and gum arabic from the dissolving candy helps break that surface tension. This, in turn, makes it so that less work is needed to expand and form new bubbles. Additionally, Mentos candy has thousands of tiny pits, called nucleation sites, all over its surface. These pits are great places for the CO2 bubbles to form. Add to that the ingredients in Diet Coke that react with the candy: aspartame, potassium benzoate, and caffeine. Finally, Mentos are heavy enough to sink to the bottom of the bottle. So this cascade effect occurs at the bottom of the soda bottle causing it to release all of its carbonation in a very short amount of time, pushing the liquid up and out of the bottle in a spectacular way.
Here are the step-by-step instructions:
1) Place the soda bottle somewhere outside and away from anything you care about getting wet. A large grass yard is usually best.
2) Open the bottle.
3) Line up the number of Mentos you want to drop into the bottle (between 1 and 8 is usually best) but don’t drop them yet.
4) Drop the Mentos and back away at least a few feet so as not to get hit.
5) Repeat with new bottles of soda as many times as you want.
– Warm soda usually works better than cold.
– It is perfectly safe to drink the soda, but unless you like it flat you probably won’t want to. The used Mentos are perfectly fine, if a bit sticky.
– You can make geyser tubes if you want to have a little more fun with fine-tuning the results.