1 Why does Mentos make Cola “explode“? o Introduction o The Phenomenon o Different Explanations o The Composition of Cola o CO 2 in Cola o Henry‘s Law.

1

Why does Mentos make Cola “explode“?

o Introductiono The Phenomenono Different Explanationso The Composition of Colao CO2 in Cola

o Henry‘s Lawo Two States of Equilibriumo CO2 in Solution

o The Bubbles – Young-Laplaceo The Bubbles – Nucleationo The Mentos Effecto Coca Cola vs. Diet Coke vs. Cheap

Cola

Philipp Schüdel- Why does Mentos make Cola “explode”?

2

Introduction


3

White Mentos, thrown into a bottle of

Cola, results in a violent eruption of the

soda-drink

It is found, that this works best with

Diet Coke but the principle works with

any drink containing CO2

Why does that happen?

Why does it work best with Diet Coke?


The Phenomenon

4

A chemical reaction? According to a

certain “professor“ from Brasil, some of

the aromas in Mentos and the

Acesulfam K found in Diet Coke react

to give an explosive substance called

Ta9V4.

Catalysis of the desorption of CO2 by

heterogenous nucleation


Different Explanations

5

Main ingredients of normal Coca Cola: water, sugar,

CO2 (called carbonic acid), phosphorus acid, food

dyes, other

Main ingredients of Diet Coke: water, CO2 (called

carbonic acid), phosphorus acid, citric acid, acesulfame

K, aspartame, food dyes, other

=> Most probable reason for violent eruption: CO2


The Composition of Cola

6

CO2 is dissolved in the Cola Mixture by applying a pressure of

approximately 4 atmospheres

Questions: - What does dissolved CO2 look like?

- What happens when the pressure is reset to 1

atm? (opening of the bottle)

In approximation, Cola can be described as a solution of CO2 in

water. For such a system, Henry‘s law can be applied.


CO2 in Cola

7

The chemical potential of CO2 in water is

It has to be in equilibrium with its gas phase

The equation can be transformed in a way that the term on the left is a constant.

That means that the term on the right side has to be a constant, too

For an ideal solution, we obtain Henry‘s law


Henry‘s Law

8

Another interesting application of Henry‘s law: The

so called “Martini Effect“:

Divers can suffer from a sort of drunkness in deep

waters. This is due to the higher solubility of N2 in

blood at higher pressure (Henry)

An empirical law connects the depth of the diver to

the amount of Martinis he would have to drink in

order to get the same effect. Every ten meters

corresponds to one Martini where the feeling of

being drunk starts at 30 meters.

Because a Martini is not a very common unit, a

recalculation has been done to form the “Beer

Effect“ according to which every 17 meters is like

drinking half a litre of beer.


The Phenomenon

9

Henry‘s law can also be written this way: c(CO2)= KH*p(CO2)

with KH= 0.034 atm*l*mol-1 at 25°C

Sealed bottle of Cola:

p(CO2)= 4 atm => c(CO2)= 0.136 mol*l-1

Opened bottle:

p(CO2)= 2.96*10-4 atm => c(CO2)= 0,010 mmol*l-1

How does Mentos help in getting from one state of equilibrium to the

other?

What does CO2 dissolved in water look like?


Two States of Equilibrium

10

Contrary to common belief, CO2 in water is not

carbonic acid H2CO3 or hydrogencarbonate HCO3-.

Only about 1% of the dissolved CO2 reacts to give

these species. In Cola, this reaction is even further

reduced due to the low pH (phosphoric acid).

According to some scientists, CO2 in solution

corresponds to small bubbles of a size of around

100 nm being dispersed in water. That would mean

that it‘s not an actual solution but a metastable two

phase system.

The best explanation is given by the CO2 forming a

hydrationkomplex with 12 water molecules


CO2 in solution

11

How does the system get to equilibrium?

Bubbles formed in the solution are only stable above a certain diameter due to the surface tension and the

pressure difference between the inside and the outside of a bubble.

The free energy of the surface is G= 4r2where is the surface tension

A change of the radius of the bubble results in a change of the free energy: G= 8rdr

This is compensated by the pressure-volume-work

p*dV= p*4r2dr

In equilibrium, those two terms are the same and we obtain the Young-Laplace-Equation:

p= 2/r

One can see that the difference in pressure and therefore the instability of the bubble is smaller for small

surface tensions and big bubble diameters.


The Bubbles - Young-Laplace

12Philipp Schüdel- Why does Mentos make Cola “explode”?

The Bubbles - Nucleation

Free energy

-2

-1,5

-1

-0,5

0

0,5

1

1,5

2

0 0,2 0,4 0,6 0,8 1 1,2 1,4

radius

free

en

erg

y

volume => -r3

surface => r2

free energy

maximum

All units in this diagram are arbituary

13

In a homogeneous solution, the bubbles can only

surpass the critical diameter through pressure

fluctuations. This is called homogeneous nucleation.

Another example of homogenous nucleation are hand

warming pads, where an overcritical liquid is crystallized

by inducing nucleation through a charge emitted by a

small metal plate.



The process of nucleation can also be catalyzed,

which is called heterogeneous nucleation. A good

example is rice which is put into Weizen. The CO2

in the beer can form bubbles on the rice-surface

which grow and make the rice “dance“.



The formation of raindrops is also a

nucleation process. Rain can only occur

if small particles like dust, pollen etc. are

present which is why it never rains in the

Antarctic.

Furthermore, in regions with high

particle concentration, like big cities,

there are too many nucleation sites.

Because of that, the raindrops can

never grow enough in order to be able

to fall.

15

How do Mentos affect the CO2 in solution?

Atomic Force Microscopy (AFM) pictures

have shown that Mentos have a very rough

surface.


The Mentos Effect

On the cavities of this surface, CO2-

molecules can accumulate to form bubbles

which surpass the critical size.

16

Why does the Mentos-Cola experiment work best with

Diet Coke? => Higher CO2 concentration?

According to the Young-Laplace-equation ( p= 2/r ) a

higher surface tension means that for a given bubble

size, the pressure difference between the inside and the

outside of the bubble is bigger than for a lower surface

tension. That means that the bubbles in a system with

high surface tension must be bigger in oder to be

stable.

Surface tension measurements of normal Coca Cola,

Diet Coke and cheap Cola showed that there is almost

no difference.

The reason for a higher CO2 concentration could also

be a higher pressure applied in the production process,

but an actual measurement of the amount of dissolved

CO2 showed no difference between the sodas.


Coca Cola vs. Diet Coke vs. Cheap Cola

17

In conclusion, the real reason

why the experiment works best

with Diet Coke has yet to be

found. The problem seems to be

a bit more complicated than

expected and there is no valid

explanation found so far.


Coca Cola vs. Diet Coke vs. Cheap Cola


Thank you for your attention and have a

nice day!

1 Why does Mentos make Cola “explode“? o Introduction o The Phenomenon o Different Explanations o The Composition of Cola o CO 2 in Cola o Henry‘s Law.

Documents

cola o henrys law o

composition of cola

cola mixture

composition of cola

mentos effect o coca

cheap cola philipp schdel

o introduction o

solution o