WHAT' YOU'LL NEED
LET'S GET STARTED!
Note: Set up all your experiments outside on a tray where it'll be okay to get a little messy.
Two optional experiments:
EXPERIMENT 1: First, if you've never done the standard Mentos and Coke experiment, let's do that now. Open the first soda bottle and drop about 5 pieces of Mentos candies in at once. (You can use a small piece of rolled up paper to funnel the candies in). Watch the explosion!
EXPERIMENT 2: In our Mentos and oil experiment, we'll be using just one piece of Mentos candy. Let's first see what happens without the oil. Open the second soda bottle, and place just one candy inside. Here's what happened to ours:
Okay, now for the Mentos Lava Lamp experiment!
EXPERIMENT 3: The Lava Lamp!
WHAT'S GOING ON?
So many questions!
1) Why does the soda stay in the bottle and not mix with the oil?
As you may have heard, "oil and water don't mix"! If you poured water and oil together into a glass, they would separate, with oil on top and water on the bottom. But why is that?
Well, water is more dense than oil. Density is a measure of how many things you can pack into a space. Water has more molecules packed into it than oil does, making oil 'lighter' than water, so it goes to the top. Oil is also made up of hydrophobic molecules ('hydro-' meaning 'water', and '-phobic' meaning 'afraid of'), so oil repels water away from it.
Well, the diet soda you used is made up of mostly water, so it just hangs out in the bottle, happy to have the oil rest on top of it.
To learn more about the density of different solutions, try out any of these other 20 Minute Labs:
2) Why does the Mentos candy cause the soda to bubble out like that?
We mentioned that the soda we used is mostly water. Well, it's also got some artificial sweeteners in it (we used diet Coke because it doesn't use real sugar and therefore is less sticky - helpful in the cleanup!), but more importantly it has carbon dioxide gas in it. In a soda-making factory, carbon dioxide is pumped into the coke at high pressure so that the gas will dissolve into the liquid. But that gas wants to escape back out of the liquid back into its gaseous form.
Have you ever noticed that when you pour a soda into a cup, little bubbles often form on the walls of the glass? That's because there are often tiny pits in the imperfect surface of the glass, which the carbon dioxide takes advantage of to form into gas bubbles that can rise up and out of the liquid.
Any place that creates a little nook or cranny for carbon dioxide gas is called a nucleation site. If you stuck your finger into a soda, the gas would find all the nucleation sites on your skin and form bubbles! This process is called nucleation.
Here's where Mentos comes in. Mentos candies are sprayed many many times with a candy layer on the outside. This provides millions of tiny pits (nucleation sites). A Mentos candy also happens to be heavy (very dense!), so it sinks down to the bottom of the soda bottle.
The carbon dioxide gas soon discovers a whole host of nucleation sites and goes crazy turning into bubbles that then push the liquid up and out of the bottle!
Because the bottle is immersed in oil, the liquid that rises out turns into globs of soda (remember - the oil's hydrophobic molecules prevent the water from mixing!). These bubble-like globs fall down to the bottom of the jar (just like a lava lamp!) because of their density.
This experiment is an example of a physical reaction, because molecules are just rearranging. For an example of a chemical reaction (where two things mix together to make an entirely new thing), try our 20 Minute Lab: Lava Lamp in a Glass.
For more exciting experiments, check out our Yellow Scope science kits on the Shop tab of our website!