The Scientific Method Example – Mentos & Diet Coke
Introduction:
Mentos and Diet Coke is a combination that has often been talked about over many years because of its
supposed exhilarating reaction when combined together. YouTube videos, MythBusters, an episode of
David Letterman, and many others have shown the reaction of an immediate foaming of the coke
creating a fountain-like reaction. The height of the fountain and the length of the fountain seems to
vary from test-to-test, depending on different factors and variables.
The explanation of this reaction has also been discussed to many different degrees. Carbon dioxide,
Mentos “pits” or “nucleation sites” (where carbon dioxide bubbles form), the weight of the candy, and
the nature of coke itself all play a role in this reaction.
Not having the opportunity to witness this reaction myself, this carefully controlled experiment will
hopefully answer the questions I have surrounding Mentos and Diet Coke, and confirm the predictions I
have towards it.
Purpose:
The purpose of this experiment is to confirm the many reports of a reaction occurring when mixing
Mentos candy with Diet Coke. The reaction being an immediate foaming of the cola into a fountain-like
display.
Hypothesis:
If I place an original Mentos candy into a bottle of Diet Coke, a reaction of foaming and fountain-like
response would occur. More specifically, I predict the fountain to be about 1m in height and last for
approximately 10 seconds. I believe this will happen for a couple reasons. Firstly, my research tells me
this is a common occurrence, and I’ve seen it happen through videos. Secondly, the reasoning behind
the reaction seems very logical to me. The fact that the Mentos candy has many moon-like pits for
carbon dioxide bubbles to form, combined with the fact that the nature of Diet Coke being very “gassy”
and easy to foam (even by just shaking it), it would seem reasonable for this fountain-reaction to occur.
Variables:
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Independent Variable: The candy – The Original Mentos mint candy vs a plain controlled candy.
Dependent Variable: The reaction once the candy is changed to Mentos. I will be looking at the
height of the fountain and how long the fountain lasts.
Controlled Variables: Diet Coke, size of bottle, number of candies placed in the coke, temperature.
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Materials:
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1 pack of Original Mint
Mentos candy
1 pack of mint Tic Tacs
2 Umbrellas
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1 2L bottle of Diet Coke
Stop Watch
Sheet of paper
2 graduated cylinders
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2 meter sticks
Table
1 Cue Card
Procedure:
Setup:
1. Set up experiment by securing the bottle on the ground in a way that it won’t tip over upon a
potential reaction. Set up the meter sticks (together) vertically from the top of the bottle. One
partner may want to stand on a table to achieve the height needed for the measurement.
2. Unwrap the Mentos candy and place them in a similar position into a rolled up piece of paper. Open
the Diet Coke (for the first time) and place the cue card on top. The Mentos rolled in paper will sit
on top of the cue card. This is how you can carefully and accurately slide the candy in the Diet Coke.
Tic-Tac:
1. Have the stopwatch ready for immediate reaction, and carefully place the Tic-Tacs into your
controlled bottle of Diet Coke. You can use your hands to guide the Tic-Tacs since the candy is very
small.
2. Start the stop watch once fountain/overflowing starts, and time how long it will last. Stop the time
once the fountain/overflowing stops. This score will be recorded into a quantitative observation
table.
3. The experimenter on top of the table will observe how high the fountain reaches. This score will
also be recorded into a quantitative observation table.
4. To see the quantity of Diet Coke that exploded, record the amount of soda left inside the bottle.
5. Close lid of Diet Coke, and clean up any mess caused by the potential eruption.
6. Record your qualitative observations.
Mentos:
1. The procedure is the same as the Tic-Tac test, except for the administration of the Mentos. See
“Setup: Step 2” to prepare for the Mentos test.
2. Remove the cue card to release the Mentos into the Diet Coke.
3. Make sure you record all quantitative and qualitative observations.
Observations:
Quantitative Data
Mentos Type
Time of Fountain (sec)
Height of Fountain (cm)
Coke Left (ml)
Mint Tic Tac
52sec
3cm
1900ml
Original Mint Mentos
5sec
198cm
610ml
Qualitative Data
Mentos Type
Observations
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Mint Tic Tac
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Original Mint Mentos
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Diagram
A very small reaction began immediately, and the fountain lasted for a
period of time (52sec).
A very small fountain that only reached 3cm. Not much pressure/force
from the reaction.
Much of the coke was still left (1900ml).
Diet Coke turned into a light brown foam, and the fountain, with limited
force/pressure, gradually spilled over the top of the bottle.
A portion of each Tic Tac candy didn’t erupt and was left in the bottle.
The first trail failed due to the Mentos getting stuck inside our paper
tube. We decided to use the cue card as a funnel and it worked. The
Mentos easily slid into the soda.
The reaction began immediately for the second trial.
The fountain reached a height that I definitely needed a table to stand
on. Reached 198cm! However, some of the fountain was restricted due
to hitting the umbrella (still was able to achieve a score).
Much of the Diet Coke erupted with a fast flow rate with not much of it
left (610ml).
The fountain lasted for a very short period of time due to the fast flow
rate (5sec).
Diet Coke turned into a light brown foam, and the fountain, with
pressure, shot straight up vertically until the max height in which formed
the umbrella-like shape.
A portion of each Mentos candy didn’t erupt and was left in the bottle.
Observational Summary
My experiment showed a reaction that was greater than I anticipated. The fountain reached
higher and lasted longer than I expected. There was also only a little amount of Diet Coke
remaining which I didn’t anticipate. What was really interesting was the fact there were
smaller portions of the Mentos candy left over. There must be something unique about the
outer layers of the candy since the middle didn’t create the reaction.
Completing a control test also helped me with my results, as I am able to compare my data with
a second candy that has never really been mentioned amongst this phenomenon. The Mentos
candy displayed a higher height, a faster response with a greater flow rate, and a greater
eruption, as evident by the amount of soda remaining. It is interesting to note that the Tic Tacs
did have a reaction, albeit a very small and slow one.
Analysis:
Why did the reaction occur?
Based on my experiment, the common discussed reaction between Mentos and Diet Coke
definitely exists. But why does this happen? In answering this question, I refer back to my
observation of there being remnants of the Mentos candy still left in the bottle. This must
mean there’s something about the outer layer of the candy to cause this since the middle didn’t
create such a reaction. I researched reasons prior to the experiment as to why this reaction
happens, and can now believe these reasons are correct based on this finding.
My research tells me there are many microscopic pits on the outer surface of the candy. These
pits, commonly referred to as “Nucleation Sites”, allow carbon dioxide gas bubbles to form and
then escape into the liquid. When the Mentos candy sinks to the bottom, the carbon dioxide
gas provides the pressure and forces the liquid above to shoot out of the bottle.
Again, this is a logical explanation since the middle of each Mentos is left inside the bottle
causing no reaction.
Comparing Original Mentos versus the candy-coated Mentos also backs up this explanation.
MythBusters and other websites I’ve researched show how the candy-coated Mentos has a
much less effect due to the candy glaze which would cover any microscopic pits. This would
obviously limit any kind of reaction.
Experiment Setup
The setup of the experiment worked well and avoided some potential errors. For example, the
cue card enabled me to efficiently place the Mentos in the bottle before the reaction occurred.
The table also helped me to measure the height. However, I had to estimate the top portion of
the eruption since it went past the 2 meters. Despite this error, I was still able to perform this
experiment and show there is a reaction.
Conclusion:
Refer to Hypothesis
As I have mentioned previously, my hypothesis was correct in achieving a reaction between
Mentos and Diet Coke. However, the extent of the reaction is where I was incorrect. I
underestimated the height and length of the fountain of coke. My hypothesis seems more like
a prediction for a half pack, which would be a good extension of this experiment.
Extensions
Other than trying different amounts of Mentos and measuring the heights and time lengths, I
can also try to prove the theory I discovered in my research with original Mentos candy and the
fruity candy-coated Mentos. Testing and comparing the results would be interesting to see if I
can replicate the results I’ve found through my research. Furthermore, it would be interesting
to compare the different type of sodas as well.
Mentos and Diet Coke … a commonly performed experiment that is easy replicated as I have
completed in this experiment. I’ve always known there to be a reaction between the two, but
is neat to complete the experiment and see the reaction for the first time. The results and
research does open the possibilities of many other extensions as well, and is very tempting to
complete in the near future.