Those Popping Rocks! (Part I)

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Pop Rocks attached to a stopper and inserted into a water-filled eudiometer

The AP Chemistry exam is over.  The students are breathing a sigh of relief and depending on whether they are a junior or senior, are putting the commensurate amount of effort into their end-of-year independent projects.  (See my own SKYKU).  Actually, even the seniors seem to be doing some impressive work.  Those projects include studying the decaffeination process, measuring the amount of fructose in soda, AND, determining how much carbon dioxide is liberated from a package of Pop Rocks!

If you have never had a package of Pop Rocks, order one immediately from Amazon.  Or better yet, make a trip to your local vintage candy shop.  The fizzing sensation on your tongue is not to be missed.  And what is all that bubbling and cracking?  Carbon dioxide escaping from these sugar rocks.

Two of the seniors knew early on they wanted to study Pop Rocks.  They leveraged an earlier lab we did to produce and measure hydrogen gas, in which a eudiometer (a very narrow tube with one end sealed with a holed stopped) is used to collect gas via water displacement.  Precise volumes of gas can be measured this way.  Today they began their first trial.  Tuesday morning we shall see the results!

I have always been curious about how Pop Rocks were made, but simply added that question to my never-ending list of “things to look up”.  Thankfully that can be removed from the list, as one of the seniors sent me this article, from the Molecular Gastronomy Network.

I had always assumed pop rocks were some combination of sugar and baking soda.  This is not the case!  Instead, the sugar is melted and then cooled “in the presence of” carbon dioxide.  I wonder how that works, exactly.  What equipment is used?  Is it difficult?  When the Pop Rocks dissolve on your tongue, the carbon dioxide is liberated.  Do Pop Rocks have a short lifetime?  Do additional steps need to be taken to ensure the carbon dioxide doesn’t leak?  These are the questions running through my mind.

Like nearly every brilliant invention, Pop Rocks came about by accident.  According to the article, in 1956 a food chemist attempting to make a powdered soda found a way to make sugar pop.  I guess Pop Rocks provide a kind of highly concentrated soda experience.  The accidental popping sugar was sold as Pop Rocks candy in 1976.

In Part 2, I will share the students’ results on how much carbon dioxide is in these candies! Spoiler Alert: It’s probably not contributing to climate change.