No, not the (allegedly) stomach-exploding “candy.” We’re talking about real, actual rocks that, like the sugary treat, fizz and “pop” when in contact with liquid. Not all rocks do this, of course, or the world would sound like the most over-the-top fireworks display you’ve ever seen every time it rained. So, which rocks do fizz? And why?
Use this simple experiment to show students (or just interested folks you encounter on the street) the magic of natural chemical reactions.
Lemon Juice on the Rocks (Literally)
This one is really about as easy as it gets. Gather up a selection of different rocks, making sure you’ve got at least one piece of limestone or marble (or both). Then, get yourself a bottle of lemon juice or vinegar (or some of each) and you’re good to go. Paper plates are helpful, too, but not necessarily necessary.
Put each of your rocks on a paper plate—if you forego the plates, be sure they’re sitting on something that can get drenched in lemon juice and/or vinegar without getting wrecked. Then, pour some of your liquid on them, one at a time.
Watch for chemical reactions: the rocks that fizz or bubble are the limestone and marble samples. The other rocks should have essentially no reaction, unless they, too, contain limestone or marble.
What Just Happened?!
Limestone contains calcium carbonate, an alkaline substance. Marble is formed from limestone, so it, too, contains calcium carbonate. (Hard to believe the two are so closely related, as they look so very different, but it’s true, by cracky!) The lemon juice, being highly acidic, reacts with the alkaline content in the rocks to produce carbon dioxide, which in turn creates bubbles on the surface.
If you haven’t any rocks handy, you can produce roughly the same results with lemon juice and chalk. Chalk is made from a type of limestone, and therefore is calcium carbonatey.
- 365 Simple Science Experiments with Everyday Materials, E. Richard Churchill, Louis V. Loeschnig, and Muriel Mandell, illustrated by Frances Zweifel, 1997. ISBN 978-1884822674