TechnoHolics

Don’t tell me that you haven’t seen the videos of the Mentos and Diet Coke which are all over YouTube since ages. If you haven’t, you surely have heard about it from your friend or read it somewhere. This reaction between Mentos and several aerated soft drinks like Coke or Pepsi which results in a spectacular eruption is popularly known as Mentos eruption or a coke geyser. Now, why is it so popular ? It is because of the nature of this physio-chemical reaction and the easy availability of the ingredients – just bump into your local shop and get them. One more reason is that this activity is very safe. The experiment was first aired on television back in 2002 and then in 2005. Since then, it’s all over the Internet.

Diet Coke : The Mentos Effect

Diet Coke burst out to height of about 2.5m when 5 plain mentos were dropped into it.

Of course, it’s just amazing to see it erupt and reach great heights and it’s even more fun to try it yourself (not in the kitchen okay-you definitely don’t want your Mum to ask you to clean up the mess; the backyard will suffice). Here’s how you do it. Get a 2 litre bottle of Coke or Pepsi. Drop in four or five plain (mint-flavoured) Mentos and voila ! you’ll see the fountain oozing up.

What’s the Science behind this phenomenon ?

Some people initially proclaimed this to be a simple acid-base neutralization reaction as Coke is acidic due to the presence of phosphoric acid of pH around 2.8. But it is found that the pH of Coke before and after dropping Mentos to be the same. So there’s no chance of a neutralization reaction.

Experiments in a 2006 edition of the Discovery Channel program Mythbusters suggested the chemicals responsible for the reaction are gum arabic and gelatine in the sweets, and caffeine, potassium benzoate and aspartame in the Coke. Here’s what Mythbusters found out :

The physical structure of the Mentos is the most significant cause of the eruption due to nucleation. When flavored Mentos with a smooth waxy coating were tested in carbonated water, no reaction occurred, whereas standard Mentos added to carbonated water formed a small eruption, affirming the nucleation-site theory. 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.

The students at Appalachian State University in Boone, North Carolina came up with the following explanation :

Scanning electron microscope images show the roughness of mint Mentos (top and bottom left) and fruit Mentos (top and bottom right), the scale bars representing lengths from 20 to 200 micrometres (Image: T Coffey/Dewel Microscopy Facility/AAPT)

What happens if you pop in Mentos after you drink Coke or Pepsi ? Or Drink Coke or Pepsi after eating Mentos ?
No harmful chemicals are produced during this reaction. It’s all Carbon Dioxide that is liberated. Chewing the Mentos destroys the surface needed for the carbon dioxide bubbles to form. So nothing will ooze from your mouth.

Ironically, the Coke or Pepsi will come to your mouth from your stomach and perhaps even come out from your nostrils – only if you SWALLOW many Mentos as it is. Now, do you guys really swallow Mentos ? If you do, beware of the aftermath mess.

P.S : Another interesting rumor was that Coke dissolved iron nails in about four days. This popular myth is busted by John Madison in his blog post “Will Coke Dissolve a Nail?” Experiment. Regardless of whether aerated soft drinks like Coke or Pepsi dissolves nail or not, they have serious health effects (if you are in India). Coca-Cola and Pepsi has been scientifically proved not harmful in countries like US and EU nations.

In 2003, the Centre for Science and Environment (CSE), a non-governmental organisation in New Delhi, said aerated waters produced by soft drinks manufacturers in India, including multinational giants Pepsico and Coca-Cola, contained toxins including lindane, DDT, malathion and chlorpyrifos — pesticides that can contribute to cancer and a breakdown of the immune system. Tested products included Coke, Pepsi, and several other soft drinks (7Up, Mirinda, Fanta, Thums Up, Limca, Sprite), many produced by The Coca-Cola Company.

CSE found that the Indian produced Pepsi’s soft drink products had 36 times the level of pesticide residues permitted under European Union regulations; Coca Cola’s 30 times. CSE said it had tested the same products in the US and found no such residues.