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What is “Mentos Geyser?”How does it work?

Rapid phase change of carbon dioxide in beverage

Hello, I am Eiji Shimada. I’d like to present my science fair project. This is about this geyser. The science content of this project is about carbon dioxide, which is CO2 by molecule formula.

#1 place in Chemistry Division, 8th grade,Space Center Intermediate School Science Fair, 2007-2008Houston, Texas, USA.

Dec. 2007

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Purpose of this studyThe purpose is to investigate the mechanism of Mentos Geyser.

Research Questions

Q#1-1. What kind of solutions can cause the geyser phenomenon?Q#1-2. How intense is the reaction?Q#1-3. How long is the reaction duration?Q#2-1. What kind of solutes can cause the geyser phenomenon?Q#2-2. Intensity? Q#2-3. Length?Q#3. What chemical property is associated with the geyser?

-solubility -surface roughness -pressure -temperature, etc.Q#4. What is the time course of the reaction?Q#5. How is the bottling pressure with carbon dioxide(CO2)

associated with the geyser intensity?

The purpose was to investigate Mentos geyser.Did you know about Mentos geyser? I saw it first on Youtube video. And I had these questions when I saw it.

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Background-1Physical solubility of gas, as solute, into liquid, as solvent, depends on pressure (Henry’s law) and temperature. For example, nitrogen may change to gas phase and cause a disease (Decompression Sickness) when the human body (blood) is decompressed in a space suit or by surfacing from a sea diving.

The solubility of CO2 gas, as solute, into water, as solvent, depends not only on pressure and temperature. It is of chemical solubility, and dissolves more than physical solution. Water molecules hydrate CO2molecule, and CO2 reacts with H2O to yield H2CO3.

Temperature (deg C) 0 20 40 60 80 100

oxygen (mL/mL water) 0.049 0.031 0.023 0.019 0.018 0.017

carbon dioxide 1.71 0.88 0.53 0.36 - -

NASA

JAXA

The solubility of carbon dioxide is not simple. We will later learn about Henry’s law,And also chemical reaction is associated with carbon dioxide.Carbon dioxide solutes much into water.

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Background-2Bubbling of carbonated beverages, when it is added with salt, has been known for a long time (salt-out.) Recently, the combination of Diet Coke and Mentos has been highlighted for its intense reaction. Since Diet Coke is a multi-solute solution, and Mentos drop is multi-layered, the mechanism is not simple. A TV program “Myth Busters” experimentally claimed a nucleation and solute theory on 9 August 2006. A surfactant and nucleation theory is claimed by antoine.frostburg.edu.

Mentos Geyser mechanism theories found by search are:1) crevice nucleation on the surface of Mentos2) CO2 hydration breakage by surfactant additive3) some kind of interaction between solutes and CO2 molecule,

including sugar viscosity

I heard from neighbor astronaut that similar phenomenon has been known as “salting out”.Did anybody watch Mentos geyser on Myth Busters? How many?They showed it somewhat scientifically.

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HypothesisMy working hypotheses were:

A) Rapid outgassing of CO2 is due to nucleation on Mentos surface.

B) Difference in intensity of outgassing between Classic Coke and Diet Coke is due to higher bottling CO2pressure in the latter.

Rationale:A) Reaction is so fast it does not seem to allow time for dissolving

by diffusion.B) This could be the simplest theory.

Mutual interaction of solutes is an interesting subject, but for this study I chose a simpler experiment with plain soda water as the principle material.

I wanted to add something new, so I put this hypothesis B. This is a beautiful, most simple explanation why Mentos work best with Diet Coke.

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Methods-1 protocol

1. Note liquid temperature.2. Reduce liquid volume by 100mL.3. Roll in five drops of Mentos via bottle neck with a funnel.

(some experiments were with sand, detergent, etc.)4. Film geyser reaction and measure its maximum height*.5. Measure remaining liquid volume and calculate the

amount spilled*.

*As the height of geyser column (that will be spilled) represents the potential energy component of released energy, and thus thought to be proportional to the chemical energy released by the reaction, geyser height (spilled volume) was used as the index of reaction intensity.

The protocol below was repeated with each combination of solvent and solute.

Protocol was this. The point is that geyser height has a physical meaning in terms of potential energy.

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Meat(surfactant)

Perrier

Sand(surfactant)

Classic Coke

DetergentDiet Coke

SugarDiet Coke ZERO

Salt(NaCl)

Sprite

SoluteSolventcut surface of MentosNote coat and core

Methods-2 material

I wanted to try a broad spectrum of liquid and solids.Who has not ever tasted Mentos?

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Results-1 time course of Mentos Geyser

0.0sec 0.57sec 2.73sec2.67sec

3.12sec 3.36sec 6.4sec 19sec

Five Mentos tablets dropped intoPerrier, Classic Coke, Sprite, and Diet Coke

As seen from these photos, this reaction happens very quickly.

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Results-2

Sugar Sand

Beef

Detergent

Sugarwater

Core, whole, and coat of Mentos

Not only Mentos, but sand, sugar powder, salt powder, sugar water, salt water, ground beef, initiated bubbling of Perrier.Coat part of Mentos reacted immediately, but bubbling intensity was not much different from whole Mentos.

Now, an interesting part. The Mentos geyser is induced by plane sand, sugar, or salt.I grazed off coat part of Mentos, but its reaction was not impressive.

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Independent variable: Concentration of salt waterDependent variable: Level of geyser by spilled volumeInitial Volume of Perrier= 900ml

Refer to “SW” in Table: Data Summary Mentos Geyser.

ResultFrom the linier relationship in the graph,

Results-3Salt Water Concentration Dependence of Geyser Intensity

Log scale

30g of salt in 100ml of water

5g of salt in 100ml of water

1g of salt in 100ml of water

(Geyser Effect) = k log (conc. NaCl)

First, I wanted to measure quantity dependency, but because geyser reaction was so explosive, I could measure only with salt water.This graph suggests exponential relationship.

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This is the matrix of solute and solvent.

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Hypothesis B) Diet Coke has greater geyser because of higher carbon dioxide bottling pressure than that of Classic Coke.

This hypothesis was denied by a reply letter from Coca Cola company.

CO2 Pressure Difference Hypothesis(B) Denied

Also, an interesting information was obtained from the letter. Coca Cola company first makes carbonated water, then adds syrup. From my experiment results, it seems better to make syrup water first, then carbonate it, to avoid carbon dioxide gas escape. There might be other factors in manufacturing process of Coke that made them decide to start with carbonated water.

I was wondering how to measure bottle pressure, but a letter from Coca Cola company came in before I figure out how.The bottling pressure of Diet Coke was equal or less than that of Classic Coke.Thus my beautiful and simplest hypothesis B was denied.

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Answers to the Research QuestionsA#1-1. Plane soda water (Perrier), Sprite, Coke (Diet, Classic, ZERO)

can make geyser.A#1-2. Diet Coke made the highest geyser. A water column (geyser)

with a height of 3 meters equals to bottle pressure of 0.3kgG/cm2

(0.3 ata gauge = 1.3 ata absolute = 130kPa).A#1-3. The bubbling phenomenon lasted about six seconds.A#2-1. Ionic solution (NaCl), non-ionic solution (sucrose), liquid

detergent, sand, core and coat of Mentos can make geyser.A#2-2. Mentos made the highest geyser.A#2-3. The phenomenon lasted about six seconds.A#3. The correlation was found between geyser height and

concentration of added salt water. Otherwise not conclusive.A#4. Major part of reaction happened within one second.A#5. Not conclusive. [In seafloor NEEMO13 mission, a JAXA

astronaut demonstrated that opening a coke can after shaking does not yield spill at 15 m depth (250kPa = 2.5 ata abs). From it Coke CO2 pressure seems to be around or less than 250kPa.]

But many of initial research questions were answered.Do you know water rocket? It works with bottle pressure which is about 2 to 6 times the atmospheric pressure.Your bicycle tire pressure is about 4 times the atmospheric pressure at sea level.

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Conclusion1. Hypothesis (A) was not tested conclusively.2. The salt water concentration correlation suggests that

the intensity of the reaction is not totally dependent on physical surface nucleation, but with some solute effect.

3. Due to the short reaction time, it was concluded that the phenomenon was the reaction between coat part of Mentos and the solvents, possibly with surface nucleation and the coat ingredient dissolving into a solvent.

4. Hypothesis (B) was denied. The bottling pressure of Diet Coke was confirmed to be equal or lower than that of Classic Coke, as opposed to some web page descriptions. As noted above, not only physical but also chemical processes are considered to be involved in this geyser phenomenon.

As I said, hypothesis B was denied. About hypothesis A it was not tested well. But from solute quantity dependency, there is really chemical component in Mentos geyser.

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Applications1. This phenomenon can substitute some high pressure gas

cartridges. As component materials are safe, it can be used with in human body, e.g., implanted injector.

2. Toys. For example, water rockets can be launched without a special air pump.

Future Study1. To investigate solute interaction, starting with distilled water,

then carbonate it with a known pressure, and add solutes is necessary.

2. Surfactant and nucleation effects are widely studied, but direct observation techniques are scarce. Much resource is needed in this direction.

Mentos coat materialBreak capsule for activation

Carbonated fluid

This phenomenon could be applied to medical use, as carbon dioxide is a relatively safe gas when released in human body.

Finally, I can make some advice to you when you do a science project.Let your parents, sisters, and brothers work. Let them dig a hole, carry bottles, and take pictures. Then you can devote yourself in brain work.

END