Soda geyser

A Diet Coke two-liter bottle shortly after Mentos were dropped into it.

A Diet Coke and Mentos eruption, also known as a Mentos eruption or a Coke geyser, is a reaction of Diet Coke and mint Mentos candies. A two-liter bottle of Diet Coke, or of some other carbonated beverage, is used, although Diet Coke is preferred because it tends to react better. Dropping some Mentos into the bottle causes the Diet Coke to foam at a rapid rate and spew into the air. Mint-flavored Mentos are used, as fruit-flavored Mentos have a smooth coating which slows the reaction. Because of the spectacular nature of this physical reaction and the easy availability of the ingredients, the eruption is a popular subject for Internet videos. The bigger the bottle of coke the bigger the explosion.

A variation of this experiment consists of making the bottle rocket. The Mentos are inserted into the bottle, then immediately afterward, the cap is put on the bottle and the bottle slammed onto the ground cap-first. The explosion will generate a reaction like a rocket.

History

The Internet phenomenon appears to have begun with a story NPR's David Kestenbaum and Michele Norris did in April, 2006 on the Diet Coke and Mentos stunt. The Internet popularity of the stunt then spiked significantly in June, 2006 when the website eepybird.com released a popular video in which Fritz Grobe and Stephen Voltz re-created the fountain display seen in front of the Bellagio hotel in Las Vegas using a timed series of eruptions. Later Eepybird videos featured "self-activating" soda jets linked together to form a Domino Rally-style effect. In September 2007, the videos, including the "Extreme Diet Coke and Mentos Experiments" video that was viewed more than 10 million times, earned the pair the highest yearly payout of US$50,000 from the video hosting service Revver.

The earliest television demonstration of the Diet Coke and Mentos reaction was in 1999 on the Late Show with David Letterman by physics student Spencer Tyler.

Since the 2006 Internet video, the eruption has been reproduced many times by popular sources, including the television shows Numb3rs, Bones, and Ellen DeGeneres; an appearance by MythBusters cast member Kari Byron in FHM magazine; an experiment conducted by Bart Simpson on The Simpsons episode, "The Debarted"; and others. The MythBusters experiment later set the record for highest soda jet recorded, at over 29 feet (9 meters), using a nozzle.

Setting world records for the most simultaneous Mentos-and-Diet-Coke Eruptions has become a new challenge for many groups of people. The original world record - 504 simultaneous eruptions - was set on May 24, 2007, and was broken on July 10, 2007, by Circle R Ranch and Books Are Fun during a special event in Flower Mound, Texas. Guinness World Records certified the record-setting effort when independent sales representatives from Books Are Fun, a Reader's Digest Company, simultaneously dropped Mentos into individual two-litre bottles of Diet Pepsi, creating 791 geysers and reaching over 32 feet with the use of a nozzle.

The next record was set on April 23, 2008, by students of Ekonomika, the fraternity for students studying Economics, in the Belgian city of Leuven; they simultaneously launched 1,360 Mentos geysers. Then, on May 14, 2008, students at Louisville Male High School in Louisville, Kentucky, broke that record by setting off 1,800 simultaneous geysers.

The current Guinness World Record—1,911 simultaneous geysers—was set on June 19, 2008, by students of the School of Business Administration Turiba in Latvia. This record was registered by the official representative of the Guinness World Record book.

Explanation

A 2006 episode of the television show MythBusters concluded that the caffeine, potassium benzoate, aspartame, and CO₂ gas contained in the Diet Coke, in combination with the gelatin and gum arabic ingredients of the Mentos, all contribute to the jet effect. In addition, MythBusters theorized that the physical structure of the Mentos is the most significant cause of the eruption due to nucleation. Mythbusters reported that when flavored Mentos with a smooth waxy coating were tested in carbonated drink there was hardly a reaction, whereas standard Mentos added to carbonated drink formed an energetic eruption, affirming the nucleation-site theory. According to MythBusters, the surface of the mint Mentos is littered with many small holes, allowing CO₂ bubbles to form very rapidly and in great quantity, in turn causing the jet of foam. This was further supported when rock salt was used as an effective substitute for Mentos.

A paper by Tonya Coffey, a physicist at Appalachian State University in Boone, North Carolina goes into detail on the reasons and physics behind the reaction.

Popularity

One reason for the popularity of the eruption is its comparative safety. Because the interaction releases only the small amount of carbon dioxide present in the liquid, the cola bottle should not usually rupture if capped—although it is possible to break the bottle with physical force. This differs from similar demonstrations with a dry ice bomb which has the potential to generate much larger pressures depending on the amount used. MythBusters also noted when testing the experiment that, unlike other materials such as dry ice which are relatively expensive and rare, Diet Coke and Mentos can be acquired at almost any local shop in countries where Mentos are sold. Many high school or middle school science labs experiments are based on this phenomenon, as it is said to promote a better understanding of chemical or physical reactions.

Further reading

• John E. Baur, Melinda B. Baur, The Ultrasonic Soda Fountain: A Dramatic Demonstration of Gas Solubility in Aqueous Solutions, Journal of Chemical Education, vol 83 no 4, April 2006, pp577–580(registration required)
• Tonya Shea Coffey, Diet Coke and Mentos: What is really behind this physical reaction?, Am. J. Phys., Vol. 76, No. 6, June 2008 pp551–557

External links

• Human experience
• About.com Chemistry page with instructions
• Eepybird, official site