How Coca-Cola REALLY Reacts to Stomach Acid

A teacher friend and I recently discussed our soapboxes… the ideas we feel so passionate about that if our students are going to get anything out of our class, it has to be this ONE thing. I literally stand on an old soapbox to make my point.

There’s a YouTube video out there by Molten Science that drives me crazy. It’s titled, in all caps, “EXPERIMENT POURING COCA COLA IN STOMACH ACID!! – EPIC REACTION!” I’m purposefully not linking it here.

In the video, a Coca-Cola can is seen next to a glass container that holds a clear, colorless liquid. The Coke can is opened and poured into the clear liquid, which immediately begins to bubble and smoke, forming a dark, tarry substance. The container is apparently very hot to the touch.

This video has over a million views on YouTube, and nearly 12 MILLION views on Facebook. Every time it makes its rounds through my News Feed, I get furious. For years, I promised myself that someday I will be the kind of science teacher that tears down bad science that has gone viral.

Coke and Acid video screenshpt.png

When we got to our acids and bases unit this past year, I finally had my chance.

I started out by having my students watch the video. Mostly they were utterly grossed out, but a few were immediately skeptical. The biggest question they had was, “Where did they get stomach acid from?”

We hoped the ‘stomach acid’ didn’t actually come from someone’s stomach and eventually worked around to looking up the contents and pH of stomach acid.* We settled on 0.10 M hydrochloric acid as a reasonable replacement for real gastric acid.

*My favorite phrase is “You’re students in the 21st century…” to which they respond with pulling out their phones and asking Google.

I pulled the HCl bottle out of the acid cabinet and asked if they wanted to see the reaction. They immediately jumped at the chance and pulled out their phones to film the excitement.

I made a big show of putting on my lab coat, safety glasses, and gloves; carefully pouring the acid into a large beaker; and taking a deep breath before adding Coke to the acid… and then… nothing happened. It just looked like Coke.

We talked through their disappointment. We discussed how unlikely it was that this reaction actually took place in our stomach, considering the product and heat released. Most importantly, the video contained no information on its “stomach acid,” unlike all the labs we did during the year, in which the materials and methods were carefully listed so that anyone could repeat our experiment.

For the sake of time, I told my students that I tried the same reaction with different acids at a number of concentrations. But nothing happened… until I used sulfuric acid that was over 1000 times more concentrated than the hydrochloric acid we started out with.

For this demo, twice as many students pulled out their phones.* I only mixed a couple of milliliters of acid and Coke but sure enough, we created the gross, tarry substance, releasing some gas and a whole lot of heat – the test tube was too hot to touch.

*The reaction releases some nasty fumes, so make sure you work with small amounts in a well-ventilated area. A fume hood is ideal.

So what’s going on? A single can of Coca-Cola contains 28 g of sugar.* The acid dehydrates the sugar, a carbohydrate, leaving behind elemental carbon. You would get a similar product if you were trying to caramelize sugar and forgot the pan on the stove. Yuck.

*If you want to give your students a real reason to not drink Coke, have them weigh out 28 g of sugar on a balance. Somehow the poster at the dentist office doesn’t have the same effect.
Coke and stomach acid reaction
Left: Coca Cola mixed 18 M sulfuric acid. Right: Coca Cola mixed with 0.10 M hydrochloric acid (a substitute for gastric acid).

Next time my students come across a viral bad science video, they just may think back to this demo and, with a little skepticism, seek out other explanations or even try to (safely) corroborate the results themselves!

What are you passionate about that you can use to make real-world connections for your students? Let me know in the comments!

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