It is well known that when a Mento is dropped into soda, something cool happens. But, what actually happens?

The dissolved CO₂ in the soda is constantly looking for a place to accumulate and form a bubble. But, bubbles don’t form spontaneously because the water molecules keep the CO₂ molecules trapped in its weak structure (connected by hydrogen bonds).

When a Mento is dropped into the soda, the CO₂ molecules gather in small craters on the Mento, which can also be called nucleation sites. When enough CO₂ molecules gather in a nucleation site, a bubble forms and is lifted up. Using the balloon, these bubbles can be captured, and the amount of CO₂ can be measured.

The following experiment was created to show the effect of the amount of Mentos (hence, more surface area and nucleation sites) on the volume of CO₂ released by the soda.

Step 1: Defining the Problem for Investigation

Question:How does the number of Mentos affect the amount/rate of CO₂ being released from soda?

Theindependent variablein this experiment is the number of Mentos put into a soda can.

The dependent variable is the amount of CO₂ released from the soda and the rate at which it is released, as measured by the width of the balloon containing the CO₂.

Hypothesis: If a certain amount of Mentos are dropped into a container of soda, then the container with the most Mentos dropped into it will produce the most CO₂ at the fastest rate. This will happen because the dissolved CO₂ will provide the most nucleation sites to come out of the solution.

Constants:

Surrounding temperature
Type of soda used
Amount of soda used per trial
Type of Mento used

Step 2: Materials

This experiment should be conducted somewhere where the ground and wall coincide (this allows the metric tape measure to be taped to the wall), and where the temperature is fairly constant.

Safety glasses
1 Beaker
1 12-pack (cans) of soda
2 Sticks of Mint Mentos (37.5 g/ 1.35 oz)
3 Balloons
6 Rubber bands
Metric tape measure
Duct tape
Scissors
Glass bottle or reusable plastic bottle with a small top
Permanent marker
Camera (optional)

Step 3: Procedure

Gather materials
Find a location where the floor and a wall meet
Use duct tape to attach the metric tape measure to the wall around 25 cm from the floor
Cut all three balloons 2 cm from the edge (to allow the balloon to fit well over the bottle)
Place the bottle in front of the wall with the tape measure
Measure 100 mL of soda in the beaker (Figure 3.2)
Slowly pour the 100 mL of soda into the bottle and mark the height of the liquid (Figure 3.3/Figure 3.4)
Skip step 9
Pour soda into the bottle up to the line representing 100 mL
Place a mento into the balloon
Optionally begin recording a video to figure out rate
Wrap the balloon around the top of the bottle
Use two rubber bands to secure the balloon to the top of the bottle
Rustle the balloon so the mentos fall into the soda
Wait 20 seconds or until the balloon has stopped inflating, whichever comes first
Record the width of the balloon
Optionally end recording
Dispose of the 100 mL of soda and wash the bottle
Repeat steps 9-18 three times for the different trials
Replace the rubber bands and balloon with new ones
Repeat steps 9-20 with 2 and 3 mentos instead of 1

A video of steps 9-13 can be found above.

Step 4: Data

The Effect of the Number of Mentos on the Amount of CO₂ Produced

	Trial 1	Trial 2	Trial 3	Average
1 Mento	8.0cm	6.0cm	5.5cm	6.5cm*
2 Mentos	7.5cm	9.0cm	9.5cm	8.7cm*
3 Mentos	9.5cm	8.0cm	9.5cm	9.0cm*

*Note: Averages are in tenths because the data collected is only accurate up to one decimal point

Figure 4.1: Data of biggest width per trial

Figure 4.2: Average of all the trials to show the difference in rate

Figure 4.3: Data table for figuring out rate

Video: All of the trials at the same time

Next two pictures/GIFs: examples from the experiment

Step 5: Conclusion/Validity

It was hypothesized that if a certain amount of Mentos are dropped into a container of soda, then the container with the most Mentos dropped into it will produce the most CO₂ at the fastest rate. This hypothesis was supported because 3 Mentos inflated the balloon an average of 9 cm at a rate of .212 cm/sec. This can be compared to 2 Mentos, which only inflated the balloon an average of 8.7 cm at a rate of .202 cm/sec, or 1 Mento, with the balloon inflating an average of 6.5 cm at a rate of .111 cm/sec. It was observed that the difference in rate and width of the balloon was drastically larger between 2 and 3 Mentos than 1 and 2 (as shown in Figure 4.2). This suggests that the amount of dissolved CO₂ in the soda is close to being completely used up.

Repeatability: This experiment can be repeated easily due to the understandable procedure, demonstrations, the definition of controlled variables, and a list of materials with amounts included.

Precision: The data of this experiment is reasonably precise. The data clearly showed a trend, but was still fairly scattered (see Reliability for explanation).

Accuracy: The data collected in this experiment can’t be compared to a true value because there is not one for this experiment. But, the trend of the data is supported by other studies of the same subject (See sources for more information).

Reliability: The data is reliable because it is supported by other experiments, the constants were kept, and the procedure was followed closely. A human error in this experiment that lowered the reliability was that the balloon did not make an airtight seal with the bottle (see trial 3 with 1 Mento in the video). This can be solved by using a tighter rubber band or by using two rubber bands (see trial 3 of 3 Mentos). Two additional constant variables that should have been kept are the time waited before recording the data, and the type of balloon used. These would both increase the reliability of the data by raising the precision of the data.