Posted by Eric Troy on 16 Apr 2017 21:26
A video on YouTube entitled 'Experiment Pouring Coca Cola in Stomach Acid!! - Epic Reaction!,' or 'How Coke Reacts to Stomach Acid,' between YouTube and Facebook, has been viewed millions of times. Posted by a channel called Molten Science, it purports to show what happens when Coca-Cola comes into contact with stomach acid, or hydrochloric acid. The video starts by showing a square glass containing a small amount of clear liquid with a can of Coke sitting next to it. We cannot tell what the liquid in the glass container might be, but it is supposed "stomach acid."
The demonstrator then pours some of the Coca-Cola into the glass with the acid and a very scary reaction occurs. The solution puffs up and turns into an ugly black and brown mass, extruding from the top of the glass, while steam comes off.
How very terrifying! If that happens in your stomach when your drink Coca Cola, then you should probably never drink it! Oh, my!
So, is it real? Nah.
The acid in the glass container is almost certainly concentrated sulfuric acid. And the reaction that is occurring has nothing much to do with Coca-Cola specifically, but with sugar. The reaction is taking place between the sugar in the Coke and the acid.
Your "stomach acid," otherwise known as gastric acid is hydrochloric acid. However, since your "gastric juice" is not only composed of acid but of other secretions as well, it is nowhere near anything that might be called concentrated hydrochloric acid. Although stomach acid is a strong acid, it cannot dissolve razor blades, and it cannot react with sugar like in the video.
The video, in reality, is a demonstration of a fairly well-known reaction between sulfuric acid and sugar. In fact, the same experiment can be performed by adding pure sulfuric acid to plain old table sugar. When enough sugar is used a very fun reaction occurs. The solution begins to turn black, and steam appears. Then a black snake begins to extrude from the top of the sugar and grows into a long black snake much like the black snakes you used to make with the special fireworks. That black snake coming from the sugar is carbon.
Here is a video showing this reaction.
A little water could have been added to the sugar to help things along, but it's fun watching things slowly unfold. See how the sugar slowly turns black, then the snake starts rising and steam starts coming up. The steam is basically water that has been formed by the reaction and is evaporating. This is because it is a exothermic reaction, producing a lot of heat. What you can't tell is the smell which would remind you of caramel and also a stinky sulfurous smell due to sulfur oxide gas. Yes, the reaction is similar to what happens when you caramelize sugar. Just much more dramatic.
What is actually happening is the sulfuric acid is decomposing or dehydrating the sugar. Sulfuric acid has a strong affinity for water and it is basically removing the water from the carbohydrate, leaving behind carbon. The sulfuric acid, in fact, removes 11 molecules of water from each molecule of sucrose.
It will do the same thing with starch. In fact, if sulfuric acid "burned" your skin, it would do much the same thing, remove the water while producing a lot of heat. Sulfuric acid is used as a drying agent in many applications due to this. It will also react with plain water causing the release of steam, although these reactions are not all that dramatic.
As far as I have been able to determine, while concentrated hydrochloric acid will certainly react with carbohydrates it will not have this kind of reaction. It is possible to cause a similar reaction with pure hydrochloric acid, but it requires the application of a lot of heat. Note that no heat source was present in the video on Coke. Here is a video from Science Theater 2020 showing the same experiment with hydrochloric acid, aka muriatic acid.
As you can see, the reaction is nowhere near as quick and robust as the sulfuric acid reaction. In fact, it takes a very long time in comparison, so long that it appear our experimenter edited out some of the wait time and skipped to the end. And the end was not very exciting, with only the hint of a brownish snake starting to rise. There wasn't even much steam. All this while sitting on a lit barbecue grill. So, sure, it will work but it cannot have been responsible for the reaction in the Coca-Cola video.
The Coke video, which is clearly a ploy to generate views and revenue with scare tactics, while showing a real reaction, is entirely misleading. Here are two articles by Anne Marie Helmenstine, Ph.D., the first explaining the sugar and sulfuric acid, and the second explaining other ways to make 'black snakes.'
If you are a MythBusters fan you may already be familiar with black snake experiments. In Season 13, Episode 5, Grant mixed sugar with sulfuric acid to make a black snake but he wasn't satisfied with the slow reaction and paltry snake. Then, he switched the sugar to an unnamed organic compound. The resultant reaction was much quicker, almost instantaneous, producing a puff of smoke and a gigantic carbon worm that went up and up.
The video below shows the "Explosive Polymerization of p Nitro Aniline" by dehydration using sulfuric acid. The black snake column is not as impressive as Grant's, but it produces a nice puff of smoke and the snake grows in the blink of an eye.
You've probably drunk a few cans of Coke before. Yet, you've never had a black carbonous snake explode out of your mouth. Nor have you choked, or reacted in any way that would indicate such a reaction had occurred. Many people have sworn off sodas, and they may tend to want to believe this video, if for no other reason than to justify their soda-ban. Such a reaction is purely childish. You do not need a bogus science demonstration to justify your dietary choices. If you don't want to drink sodas, it is an entirely reasonable decision. They aren't the healthiest beverage available. If you do want to drink soda, though, you can do so without fear of giant carbonous snakes.