ExplodingSoda

Age

Elementary, Middle School, High School

Format

Hands-on, Stage Show

Materials

   Carbonated Soda (diet is preferable, as it is less messy and may cause a more dramatic effect)
   Mentos Candy (mint-flavored or fruit flavored) 

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

Always wear safety goggles and a lab coat. Do not get prepared solution in the eyes and as good as the solution may smell, do not drink or eat it. Nothing in the laboratory should be eaten or drank unless specified by the coordinator. Perform in an open area able to be safely covered with soda, as reaction will be explosive. Mixing soda and Mentos in your mouth or stomach may produce a similar reaction and pose a danger.

Preparation

Choose the amount of Mentos and size of soda bottle based on the desired size of reaction. See the “Demonstration” section for suggested reaction sizes. It is better to use warm soda than cold soda.

The experiment should be performed either outside, where cleaning up soda is not necessary, or within some sort of enclosure, such as a fish tank or a very large beaker.

Demonstration

Inserting whole Mentos candies into a bottle of soda should produce a dramatic, foaming “explosion” nearly instantly. Because it is very important that the soda be fully carbonated, it is best to drop the Mentos directly into the bottle the soda came in, rather than pouring the soda into a different container before performing the demonstration. When using more than one Mentos, make sure to insert them all simultaneously. You can do this by holding the Mentos in a stack in your hand and dropping them all in at once.

• For a 12oz soda bottle (hands-on station), use 3 Mentos. Reaction reaches ~0.5-1.0ft.
• For a 2L soda bottle (stage demonstration), use at least 5 Mentos (as many as possible!). Reaction reaches ~10-15ft.

What to Say

Of the many scientific processes at play in this experiment, young audiences should most easily and excitedly respond to the concept of carbonation. Remind the audience that soda feels “fizzy” in your mouth and explain that this is due to bubbles of carbon dioxide gas trapped in to the drink. Ask them if they know why soda goes “flat” and loses its “fizzyness” when it gets left out for too long. Explain that it is because all of the trapped gas escapes and there is none left to bubble out.

First insert some innocuous object into the soda, such as a coin or pencil. Have the audience notice that bubbles appear on the surface of the object. Remind them these are trapped bubbles of carbon dioxide. Before you insert the Mentos, explain that certain chemicals in the mints make the gas bubble much more quickly than with the innocuous object.

When performing the experiment, inform the audience that it can be messy if not done carefully.

Why It Is

Carbonated beverages are composed of carbon dioxide (CO2 gas) dissolved in water, as well as sweeteners, dyes, and flavorings. The dissolved CO2 gas is kept within the liquid water by the pressure of the container (the bottle or can). If this pressure is released by opening the container, bubbles of CO2 will escape from the soda and produce effervescence, a “fizzing” effect. The effervescence can be increased if the volatile soda solution is disturbed by shaking the container or inserting an object into it. This is why soda bubbles up if you pour it into a new container, but not if it is just sitting around.

Two properties of the Mentos and Diet Coke make them ideal for this experiment:

The Mentos has a rough surface, covered with many microscopic pits. These pits increase the surface area of the mint by a very large amount – just like a golf ball has a larger surface area than perfect sphere would. Each pit serves as a great nucleation site – a place for a bubble of CO2 to form.

The Mentos contains gum arabic and the Diet Coke contains aspartame and potassium benzoate. Gum arabic is a surfactant that reduces the surface tension of water (see Science Theatre's Tie-Dye Milk writeup for more information). Reducing the surface tension of the water makes it easier for bubbles to form. The aspartame and potassium benzoate in the Diet Coke also reduce the energy necessary for bubble formation.

Experiments suggest that caffeine is not a significant ingredient in this reaction, primarily because there is only a very small amount of caffeine in soda (see reference 2).

When the Mentos is dropped into the soda, the disturbance of the solution, the appearance of a rough surface rich with nucleation sites, and the chemicals in the Mentos and Diet Coke all contribute to the rapid development of CO2 bubbles. The appearance of gas bubbles on the candy is visible during the experiment. This sudden and rapid formation and escape of CO2 bubbles sends a powerful flow of CO2 gas spewing from the container, taking the liquid soda along with it.

Real Life Examples

Rapid-foaming phenomenon can be observed when ice cream is added to root beer when making a float, or when pasta is added to boiling water. In the latter case, evaporated water molecules are released from the boiling water rather than CO2.