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Using Diet Coke and Mentos
to teach scientific inquiry
by Tracey Arnold Murray
T
he combination of Diet Coke and Mentos is a
fun and messy example of the change in states
of matter. Adding mint Mentos candy to a twoliter bottle of Diet Coke produces a fountain of
soda foam that can reach 3 m high. A demonstration
of this can get a “Wow” out of most audiences, usually followed by a “Do it again!”—but can it be used
to teach anything? The answer is a definite “Yes,” and
what follows is a guided inquiry activity that allows
middle school students to do this experiment inside
(with a minimum of mess). Students measure the
heights of the soda fountains produced by different
combinations of soda and candy to determine what
factors are important in producing the fountains. This
activity, in its simplest form, will provide middle school
students with a safe and fun example of what happens
when matter changes states, and a better understanding of scientific inquiry, including the development of
a hypothesis, the development of experimental methods, and the interpretation of data.
This activity can be split into two phases, demonstration
and experimental design (about one hour) and experiment and analysis (about one hour). Figure 1 shows a
minimum list of materials needed to do this activity.
To allow students to explore Diet Coke and Mentos
inside, one piece of candy is added to a 20-ounce bottle
of soda. Adding only one piece of candy to the soda
results in a measurable fountain, but not one that will
spray soda all over the room. This should be done
inside a tub that can catch the soda as it comes out
of the bottle. For the reaction to work, an unopened,
unshaken bottle of soda is required for each trial. The
soda cannot be moved into different containers or split
in any way; anything that will release carbonation from
the soda will ruin the reaction. If there is a sink available in the classroom, students can empty their tubs
frequently, which will aid in cleanup. If students follow
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Photography courtesy of Michael Murphy
Preparation and hints
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the directions and add only
one piece of candy to each
soda bottle, there should
be little spray on the table
surface to wipe up at the
end of the lesson. Spills are
possible, so keep an eye on
students and remind them
to keep bottles capped unless they are about to be
used. Used candy should
go in the regular trash and
any leftover soda should
be poured down a sink and
the bottles recycled. As in
all experiments, students
should not eat or drink any
of the materials.
Expected results
(using minimum
materials)
FIGURE 1
Minimum materials needed to do this activity
Materials
Details
Two-liter bottles of Diet Coke
For the demonstration, two bottles
minimum (more is recommended)
Rolls or bags of mint Mentos candy
The two-liter demos take 7 to 10 candies, the
student experiments will take 1 candy each
Device to get 7 to 10 mint
Mentos into two liters of Diet Coke
A paper tube the size of the Mentos works;
alternatively, purchase a commercial product
20-ounce bottles of Diet Coke, Coke,
and Sprite
See the experimental design to estimate
how many you will need
One roll or bag of fruit-flavored Mentos candy
One candy per experiment
One bag of any mint-flavored Life Savers
One candy per experiment
One bag of fruit-flavored Life Savers
One candy per experiment
Tubs to catch the soda fountains
One per student group; must be able to
hold at least 20 ounces of liquid
At a minimum, you will
Meter sticks
need Coke, Diet Coke,
and Sprite to demonstrate
Napkins or paper towels
the importance of caffeine
(Coke versus Sprite) and
Chemical splash goggles
artificial sugar (Diet Coke
versus Coke). Diet Coke
should make the tallest
fountain, followed by Coke, then Sprite. Mint Mentos
and mint Life Savers appear to make equally tall fountains. Fruit-flavored Life Savers do not produce a measurable fountain. I have gotten different results with
fruit-flavored Mentos. When I first did this activity,
fruit-flavored Mentos were coated and did not produce
a fountain. More recently, the fruit-flavored Mentos
have worked almost as well as the mint-flavored ones.
The reason for this is the roughness of the candy; the
now uncoated fruit-flavored Mentos are as rough as
the mint. What happens when the candy is added to
the soda is a physical reaction—the carbon dioxide
dissolved in the soda all becomes a gas at once due
to the presence of nucleation sites on certain types of
candy. A nucleation site is a place where a bubble of
carbon dioxide gas can form. When you have a lot of
nucleation sites enter the soda, in the form of candy,
this causes the rapid expansion of the gas, which is
Must be able to get wet without
permanent damage
Lots of extras on hand
One pair for every student and the teacher
forced out of the top of the soda bottle (and carries
some liquid with it). Rough surfaces provide the most
nucleation sites for the formation of carbon dioxide
bubbles and are necessary to make a fountain. You
should check the Mentos you purchase to find out
what type of reaction to expect.
Demonstration
Students need to obser ve this reaction and get
excited about exploring it before they begin forming potential hypotheses. They may have done
this experiment themselves or watched it on TV
or online. Ask students if they have obser ved this
phenomenon before and if they have any idea what
causes the fountain. Students who are familiar with
the fountains may also have experimented with
different sodas or candies prior to class. Record
any results the class already has to compare to the
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results the class will collect during their
experiments. Because not ever y student
FIGURE 2 Sample materials lists
will have seen this before, it is still best
(and fun) to do a large-scale demonstraCandy labs
Soda labs
tion for students. To do the large-scale
•
20-oz
bottles
of
Diet
Coke
• Mint Mentos
demonstration, take students outside and
•
Mint
Mentos
• 20-oz bottles of Diet Coke
place 7 to 10 mint Mentos into a two-liter
•
Fruit-flavored
Mentos
• 20-oz bottles of Coke
bottle of Diet Coke. If you are unable to
•
Wint-O-Green
Lifesavers
• 20-oz bottles of Sprite
do the large-scale demonstration outside,
•
Fruit-flavored
Lifesavers
there are multiple videos of this available
online. If you type “Diet Coke and Mentos”
into any search engine, you will find many
[from what students know and from what they saw in
examples. The videos should still provide students
the demonstration, describe why this will happen].
with some obser vations and motivation to perform
The labs should write all their potential hypotheses
the rest of the lesson.
down as finished statements, even though they
After they have seen the demonstration, pose the
will only test one of the hypotheses during the exfollowing questions to students as a class:
perimental part. Once all the labs are finished with
their hypotheses, pose the following questions to
• What factors are important in this reaction?
students as a class:
• Which important factors are from the candy?
• Which important factors are from soda?
• What hypotheses did the Candy Labs develop?
• Are there any other hypotheses that need to
You may need to prompt students on what types of
be added?
“factors” may affect the reaction. Examples include the
• Are the hypotheses testable?
sugar found in soda, the mint flavoring in the candy,
• Are they using all the available materials?
the sugar in the candy, the caffeine in the soda, the
carbonation of the soda, the number of candies used,
This should encourage the labs to test different
the size of the soda bottle, the coloring in the soda,
hypotheses
and will ensure that all of the materials are
the temperature outside, etc. During this discussion,
used to get the most data about the factors. Although
record potential factors; these are the beginnings of
you do want students to test different aspects of the
the hypotheses students will develop in the next part
reaction, it is best if at least two labs test the same hyof the activity.
pothesis. Repeat this process with the Soda Labs.
Break the class into “labs” of three to five students.
Provide students with a list of available materials
Experimental design
(Figure 2). One set of labs (roughly half the class)
will be the Candy Labs and will develop and test hyIn order for this activity to teach students how scipotheses related to the important factors in the candy.
ence is done, they need to think and put their ideas
The other set of labs will be the Soda Labs and will
on paper before they start experimenting. Students
develop and test hypotheses related to the important
also need to work as a class to use their resources
factors in the soda.
wisely. Students will have some constraints to keep
Allow the lab groups 10–15 minutes to develop
in mind as they develop their experimental meththeir hypotheses. At this point, each lab should
ods. Besides the constraint that is due to the type of
tr y to come up with a few hypotheses they would
lab they are in (Candy or Soda), students will also
like to test. Remind students that a hypothesis is
have a common method to minimize the mess in
a testable statement that says what will be tested,
the classroom (one candy in a smaller soda bottle).
predicts what the results will be, and explains why.
After explaining these constraints and goals to stuThe hypothesis should be written in the “If…then…
dents, ask each lab to choose a hypothesis to test
because…” format. For example, “If [the factor to
and develop an experimental method that they will
test] is used then [predict what will happen] because
use to test it.
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FIGURE 3
Student activity sheets
Goals for this activity:
• Experience the process that scientists use to develop and test hypotheses
• Observe an example of a physical change in state
of matter, CO2 dissolved in a liquid converting to a
gas
• Remember that science is fun and happens
everywhere.
Our methods: In order to test our hypothesis we will…
Day 1 (introduction and planning)
Your teacher will get the materials you need to do
these experiments at a later time. Please generate a list
of what you will need to do your experiments. Include
how many of each item you will need.
Experimental design:
Are you a candy lab or a soda lab? _______________
Work with the other members of your lab to develop
a few hypotheses you would like to test (you will have
to pick one in the end, but you want a couple to choose
from). You will have 10 minutes to develop at least two
hypotheses. Record your hypotheses here:
1.
2.
3.
Remember: A hypothesis is an educated guess about
why a phenomenon happens—it is not a prediction of
what will happen. For example, I have observed that being around cats makes me sneeze. A hypothesis I can
develop from this observation is that “cat hair causes
my allergic reaction.”
After your class discussion; put a star next to the hypothesis you will test.
Step 1:
Step 2:
Step 3:
Step 4:
Day 2 (experiment and analysis)
• Finalize your procedures and gather the materials
you asked for to do your experiments.
• Follow your procedures and do your experiments.
Remember to wear your safety goggles, and do not
eat or drink anything.
• Record your results (and any changes to your
methods).
• Organize the data you collected into a table or chart
on the paper provided by your teacher.
• Was your hypothesis confirmed?
• What data do you have to support this?
On the back of this page, record questions you still
have about what causes the fountains. How would you
go about answering those questions?
Class methods: These will be discussed as a class.
Record the class answers here.
•
•
•
•
•
How we will determine the height of the soda fountain:
How many times we will repeat each experiment:
What we will do as a control experiment:
Anything else:
Develop a set of experiments to test your hypothesis with your group. Write a step-by-step
experimental method below.
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FIGURE 4
Extensions
Topic
Details
Different liquids
The experiment can be easily expanded to include other
types of carbonated liquids that are not usually considered
soda (tonic water, soda water, etc.) or even other types
of noncarbonated liquids. You can also compare different
brands of sodas or other similar types of soda (i.e., Coke
vs. Pepsi, Sprite vs. Sierra Mist).
Different solids
Different types of candy and noncandy substances can be
explored. Items with rough surfaces will work and items with
smooth surfaces will not. MythBusters used rock salt instead
of candy in their record-breaking soda fountain. Students
can experiment with many other substances with rough
surfaces to see which would result in the tallest fountain.
Surface area
This might work best after exploring different solids. Compare surface areas of mints by cutting them in half or in
fourths.
Temperature
The temperature of the soda bottles can be changed before
adding the candy. A note of caution: Do not heat the soda
bottles. They will either explode or melt. Change the temperature by making the soda colder. Colder soda will not
work as well as warm soda because warm soda releases
the carbonation more easily.
Shaking
Shaking the bottles before opening and adding the candy
will also change the reaction. We all know what happens
when you shake soda and then open the container—be
careful! Because the carbonation is released before the
candy is added, the fountain will be smaller.
Open bottles
Leaving the bottles open for different lengths of time can affect the size of the fountain. Again, the more carbonation that
is released before adding the candy, the smaller the fountain.
Chain reactions
Have more advanced or inventive students try to replicate
some of the scenes found on EepyBird (www.eepybird.
com) or make their own series of chain-reaction fountains
where one causes the release of another.
More science
You can ask students to use the internet to find out more
about the science behind this reaction. There are many sites
to explore. MythBusters also tried to figure out what the
important factors are. Students can view this segment and
compare their methods and results to those of the MythBusters.
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Discuss the methods with students. Pose the following questions
to the class:
• How are you going to measure
the height of the soda fountain
or the extent of reaction?
• How many times should we
repeat each experiment?
• What will function as a
control experiment?
The question of how to measure
the height of the fountain is possibly the most important of these
questions. This is the trickiest
part of the experimental design
and demonstrates the creativity
needed to be a good scientist. If
students choose to directly measure the height of the fountain,
there will need to be some sort
of scale behind the fountain. A
meter stick held behind the soda
bottle works well. If multiple video
cameras are available, your class
could videotape their fountains
for later measurement. If video
cameras are not available, students
will have to watch the fountain
and estimate the height. If this is
the case in your class, you need to
emphasize the importance of multiple students watching the same
fountain and deciding on a height
for each trial. Although this is
less accurate, it works fine. There
should be enough difference in
the heights of the soda fountains
to overcome the errors students
will make in estimating. A second
method for measuring the extent
of the reaction is to measure the
change in amount of soda in the
bottle before and after the reaction.
This can be done by volume or
mass difference. Volume is easier,
as students can line up the bottles
and compare directly, but it is less
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precise. Measuring mass is more precise, because it
can be accurately measured before and after the reaction, but it requires balances.
After all of the experimental methods are worked
out, students should write a step-by-step experimental
method in their science journals or on the Student
Activity Sheet (Figure 3). When the labs have their
methods written, ask students to gather the materials
they will need. This allows you to know if there will
be enough for every group. If students will be doing
the experiments on a later day, ask them to prepare a
materials list for you and then provide them with the
materials on the day of the experiment.
Experiment
By this time, students will be very anxious to begin
experimenting. Before they begin, remind students of
the importance of wearing their chemical splash goggles at all times during the experiment. Also remind
them never to eat or drink anything they are using in
experiments, even when those things are normally
consumable. Provide each group with materials, a tub,
paper towels, and chemical splash goggles, and let
them begin. In addition to doing their planned experiments, ask all groups to examine the ingredient lists
on their materials to determine differences among the
candies or sodas they are using. Students will need to
look at these to make sense of their results.
Wrapping up (data analysis)
Once students are finished with their experiments,
they should dispose of any soda or candy used in the
experiments; soda may go down the sink and candy
can go in the trash. They should also use the paper
towels to clean up any soda that has sprayed onto
their tables. After cleanup is complete, give the groups
10–15 minutes to make a chart of their data and decide
whether their hypotheses were confirmed. Students
should do this as a group but record the chart of their
data and their outcome individually in a science journal or on the Activity Worksheet. Have each lab share
their data with the class and then lead a discussion
on which factors are important in the reaction. Students should notice a difference in the heights of the
fountains using the different types of soda and should
be able to recognize that some sodas have caffeine
and some do not. Caffeine will make the soda fountain
taller. The other factor that can be easily recognized
is the different types of sugar (diet versus regular).
Ask students to look on the ingedient list for “high
fructose corn syrup” and “aspartame” if they do not
recognize the difference. Aspartame causes a larger
soda fountain. The important factor in the candy is
the roughness of the surface, which may not be apparent from these experiments. However, if students
examine the ingredients, they should find that the
candies that produce a reaction are identical in composition to the candies that do not. This should lead
to further discussion and questions—which is exactly
what should happen in science!
Once you have finished the discussion of the experimental results, you can have a discussion of the
change in the state of matter that students observed
in this experiment. The fountain would not be possible
if the carbon dioxide dissolved in the soda (liquid) did
not come out of the soda (become a gas) when the
candy was dropped in. Because gases take up much
more space than liquids, a fountain is seen shooting
out from the bottle. You can see the fountain because
some of the liquid molecules are carried along with the
gas molecules as they expand out of the bottle.
Extensions
One of the strengths of this activity is the many different ways that this experimental setup can be extended.
Some options are listed in Figure 4. Although many of
these extensions will work best for older or more advanced students, even younger students could develop
new hypotheses or methods based on their results and
continue to test these new hypotheses.
Conclusion
This inquiry-based activity is a fun and engaging way
to get students thinking like scientists. Although it
does take some class time and will cause a little mess,
students will enjoy making these soda fountains and
learning about experimental design and states of matter. The combination of Diet Coke and Mentos will
get students interested and excited about the activity,
which can accurately replicate the process of scientific inquiry for them. n
Tracey Arnold Murray ([email protected]) is an
assistant professor in the Department of Chemistry
at Capital University in Columbus, Ohio.
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