The Science Behind Diet Coke and Mentos
Since the dawn of time, man has been fascinated with blowing stuff up. Over the years, many different “bombs” have been invented for man to play with, the most recent being Diet Coke and Mentos. A schoolteacher on the David Letterman Show, Lee Marek, first made this famous in 1999. This interesting phenomenon occurs when a Mento is dropped into a two-liter bottle of Diet Coke. When the Mento is dropped in, the soda erupts into a forceful, fizzy, vertical stream. The question is: what makes this happen?
For this particular reaction, Diet Coke is the best carbonated drink to use. The ingredients of Diet Coke are carbonated purified water, caramel color, aspartame, phosphoric acid, potassium benzoate, natural flavors, citric acid, and caffeine. It is the best drink to use because of the caffeine, potassium benzoate, aspartame, and carbon dioxide bubbles in the soda. These carbon dioxide bubbles play a very important part in the eruption, which will be explained more in depth later. Now for the other key ingredient: the Mento.
Although Mentos appear smooth to the naked eye, they are actually covered with thousands of small, rocky holes. These holes and bumps act as nucleation sites, which strongly attract carbon dioxide molecules. (Schmidt, par.5) Previous researchers have discovered that only mint Mentos can be used. The fruit flavored Mentos are covered with a candy coating, that does not have the nucleation sites needed to attract the CO2 bubbles. (Schmidt par.10)
The explanation is really quite simple, once one understands it. Water molecules are strongly attracted to each other, and often form around a carbon dioxide bubble in the Diet Coke, creating a “shell” around the bubble. Only one problem: the carbon dioxide bubbles want to expand and multiply. But they can not do that with the water molecules surrounding them. When the Mento is dropped into the Diet Coke, it “pops” the water molecule shell around the carbon dioxide bubble, breaking the surface tension. The bubbles then go straight to the Mento, and collect on the nucleation sites, rapidly growing larger, multiplying and reproducing. By the time the Mento has sunk to the bottom of the Diet Coke bottle, all the bubbles are multiplying so fast they shoot out of the top of the bottle, taking some of the soda with it, causing the forceful, vertical stream of fizz.
There are two different theories to why this works. Some scientists believe that what happens is a physical reaction. Although, others think that it is a chemical reaction that is happening here. It is hard to say which theory is correct. So to better understand this controversy, the two reactions must be better understood.
A physical reaction is where the matter or material stays the same. The matter just changes its appearance. For example, a paper is cut into 15 pieces. That is a physical change. It is still the same piece of paper, but it just looks different because it has had a physical change. But if the paper was put into a fire or flame and was burned to ashes, it is not a physical reaction, but a chemical reaction, because the paper changed into another material (ashes). (mcwgn.org par. 3, 4, 5, 6)
A chemical reaction occurs when molecules; or atoms, interact with each other. It's really quite simple. For a chemical reaction to occur, a chemical change must happen first. A chemical change is when one compound changes into another compound. An example of a chemical reaction is when a steel trash can starts to rust. The iron found in the steel, and the oxygen in the air mix together, causing a simple chemical reaction: rust formation. A reaction can occur only if a chemical change happens. A chemical change is when new chemical bonds are formed and the energy is absorbed. (mcwgn.org par. 3, 4, 5, 6)
The most common theory is that it is a chemical reaction. Most scientists and scholars alike believe this because the Diet Coke changes its physical state, going from a liquid to mainly gas. The gas is the carbon dioxide bubbles that are violently erupting out of the Diet Coke vertically. Even though some of the fizzing explosion is the Diet Coke, most of it is the gas. So, since the Diet Coke changes from a liquid to a gas, it is considered a chemical reaction by most educated people who have thoroughly investigated this interesting phenomenon.
Diet Coke is the best carbonated drink to use. Diet Pepsi lacks some of the key ingredients in Diet Coke, therefore affecting the outcome of the fizzy eruption. It has pretty much the same stuff in it, just not enough. In a recent test,
Perrier Carbonated water, Coca Cola Classic, Sprite Zero, and Diet Coke were all tested.
Above: From left: Perrier Carbonated water, Coca Cola Classic, Sprite Zero, and Diet Coke. (wikipedia.org/Deit_Coke_and_Mentos par. 4)
Most other candies do not work, because they lack the necessary nucleation sites. Tic-tacs work, but they are smaller and don't produce such dramatic results.
On the popular television show MythBusters, the hosts tried this same experiment with rock salt. They claim that the rock salt worked even better than the Mentos. This is possible, because the rock salt has similar amounts of nucleation sites. They also said that because rock salt worked so well, table salt (regular salt) would work just as well. Well, it doesn't. Many other sources have tried using table salt, and none of them could get it to fizz at all. (wikipedia.org/Deit_Coke_and_Mentos par. 4) The reason is that the chemical structure for salt is cubic, so it is not as coarse as the Mento.
Diet Coke originated with Coca Cola Classic in 1886. Over the years, Coca Cola began to evolve. In 1983, it became caffeine free. 1985 brought Cherry Coca Cola. In the same year, Coca Cola changed their recipe slightly, becoming Coke. The new millennium brought Coca Cola Lemon, in 2001, but it stopped production in 2005. Vanilla Coke came in '02, but was also stopped in 2005, and brought back in 2007, due to the popularity of the flavor. In 2005, Coke Zero appeared.
There are many different types of Coke, so there are many different was to do this experiment. But still, the best way is to use Diet Coke and mint Mentos.
The temperature of the Coke can also affect the outcome of this experiment. Cold Diet Coke does not work as well. However, if the Diet Coke is left out in the sun for a few hours until it is hot, the eruption is much, much more explosive. Below is a photo of hot Diet Coke on the left, and cold Diet Coke on the right, with regular temperature in the middle.
As you can see, the temperature greatly affects the height of the geyser. (Schmidt par. 23)
Warning: do not swallow a Mento and drink Diet Coke in the same gulp. It can and will kill you.
So in conclusion, the best way to do this experiment is to use mint Mentos with hot Diet Coke. This still proves to be an interesting phenomenon for man and child alike, and will be until the next explosive geyser of edible compounds is discovered.