Sidewalk Science: Mentos Geysers!

Stand back! The next generation of Mentos-dropped-in-soda scientists are coming through! The chewy, minty candy has been plopped into two-liter soda bottles for years. Often used by science teachers, it’s the quintessential example to demonstrate the release of carbon dioxide, complete with a real “wow” factor. What is it about carbonated soda and Mentos? What about the reaction makes it fizz and fly? Is there a different reaction with full sugar sodas compared to their diet counterparts? Enough chatter! THIS is a science experiment for the ages. Let’s do it!

Materials

The supplies for this frothy activity:

2 liter sodas

Lots and lots of mint Mentos

A tube/tool to dispense the Mentos

First, pick a nice day to conduct your experiment. This is completely an outside activity. Unless you’d like to clean sticky soda off your nice floors, head to the great outdoors with lots of space to spill (and run from the shooting geysers).The driveway proved to be an ideal spot. Using the garage door and easy-to-peel-off painters’ tape, we labeled the door in one-foot increments, so we could measure how tall each soda geyser rose.

Soda Options

Which brings us to the soda choices. We went with four different kinds:

Full sugar cola

Diet cola

Full sugar lemon-lime soda

“Zero” calorie cola

How high will they shoot when they react with the candy? Other than an outdoor space, we found the Mentos dispenser to be the most crucial part of this experiment. While it is tempting, do not drop the Mentos into the soda through the paper packaging roll they come in. They will not fall at the same time, and an even “drop” is necessary for the desired soda spout. Instead, we fashioned a dispenser slightly bigger than the circumference of the Mentos. Using a toilet paper roll, cut it length-wise, and tape it together again. Test it to make sure the Mentos will drop through.

Experiment Time

Time to take it to the driveway. Open up one of the two-liter bottles (we used Diet cola first). Position it in a place where onlookers won’t get splashed and the person putting in the candy has space to make a break for it. Hold the homemade dispenser in one hand, and place a thin piece of cardboard on the bottom of the tube with your other hand. This keeps the Mentos from dropping out until its time. Have a fellow scientist help you drop 10 Mentos into the tube. Position the cardboard and tube over the opening of the soda bottle. Then, like a magician sweeping off a tablecloth, remove the thin cardboard so the candy can drop in. Then…RUN! Ka-boom! The soda geyser was huge! Now let’s try other sodas and measure our results. We quickly discovered that the “zero” calorie soda was the winner with the highest blast, with the diet soda in a close second. So WHY does this happen?

The Science behind a Mentos Soda Geyser

Soda is made up of sugar or artificial sweetener, flavoring, water, and preservatives. Carbon dioxide, which is pumped into it at the soda factory, gives soda its bubbly state. When it’s contained, carbon dioxide bubbles have a lot of pressure. When you open a can or liter of soda, the “fffffttttt” you hear is the release of gas. It is the formation of carbon dioxide bubbles that rise to the top, pushing any liquid out of the way. Shaking a bottle or can of soda pushes those bubbles to the inside walls of the container. The microscopic “pits” on the side of the plastic or can are called nucleation sites, allowing a place for the bubbles to cling. Mentos candy has those same nucleation sites – actually thousands of them. Carbon dioxide bubbles form in those pits when the candy is dropped in, forcing them to rise to the surface. Equally important to note, the Mentos are heavy and sink to the bottom of the bottle. The gas released at that moment pushes the liquid up from the bottom in a huge blast. And because the artificial sweeteners in our two sodas are actually chemical, the “zero” calorie and diet soda lowers the surface tension in the drink, causing a bigger reaction! Happy soda blasting!! Save it for later!