Watch Sulfuric Acid Melt a Sponge In Slow-Motion

Here's a terrifying and fascinating chemical reaction to start your Monday right. In a slow-motion video, sulfuric acid rips apart a sponge. We'll let you admire the show, and explain what's happening.


When a new lab assistant is given some sulfuric acid, they are traditionally rapped on the head three times and told to never, ever add water to it. That sounds like instructions for a gremlin, and not acid. As it turns out, adding water to acid is more dangerous than creating small monsters. Gremlins you have to feed after midnight in order for them to go evil, but acid will turn on you right away. The acid is denser than water, so adding water to it will leave the water on the surface while it's having a reaction with the acid. That reaction will involve the acid — in the case above it's sulfuric acid, or H2SO4 — donating a proton to the water, making the water H3O+. The reaction is highly exothermic, meaning that the water will sometimes boil. Boiling water on a lake of acid can be very nasty indeed.

Acid reacting with water is not the only thing that's happening in this experiment. The sponges contain cellulose, which is made up of carbon, hydrogen, and oxygen in the following combination: C6H10O5. Eagle-eyed readers will notice that if you take away the carbon, that's five water molecules stapled together. Sulfuric acid desires water so much that it can rip the water off a molecule in order to have a reaction it. (In classrooms we often see this demonstrated with sugar. The acid rips water molecules off the sucrose molecules.) The sulfuric acid is tearing the cellulose in the sponge apart and donating a proton to the resulting water.


[Via The Dehydration of Sucrose, Royal Society for Chemistry.]

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