Friday, September 23, 2016

Homeschool Geology: The Acid Test for Carbonate Rocks

One of the freedoms of homeschooling that is deeply important to me is our ability to do projects that are not watered down in deference to a child's age or level of experience. If I think that my second-grader can handle writing a ten-page research paper, then that's what I can mentor her to do. If I think that my fourth- and sixth-grader can handle a six-month study of World War 2, then that's what we study for six months. If I think that my fifth- and seventh-grader would be interested in dissecting a shark (and they are!) or can safely handle dangerous chemicals, then I buy them a preserved shark specimen AND a small bottle of hydrochloric acid.

Unfortunately, some materials can be difficult for a homeschooling parent to purchase. For the shark specimen, for instance, I super wanted the pregnant shark triple-injected with latex that Will was absolutely drooling over, but Carolina Science doesn't ship to residences (seriously, though--what mischief could I possibly get up to with a preserved shark in my own house?), so I had to settle on this less desirable, poorer quality shark from Home Science Tools. Home Science Tools also let me purchase hydrochloric acid, something else that Carolina Science won't, sigh, so that the kids and I could use it to test rock and mineral specimens.

Hydrochloric acid is useful for positively identifying carbonate rocks and minerals, which we have a lot of here in Indiana. Yay, limestone! To perform this test at home, you will need:
  • hydrochloric acid
  • very small glass bottle. You can also use a small plastic squeeze bottle, but I felt more confident storing hydrochloric acid in glass.
  • three eyedroppers. These are a dime a dozen (sometimes literally, if you keep your eye out for deals!), so I disposed of the eyedroppers that the kids used for the hydrochloric acid and the dilute solution. When we work with the acid more extensively, I might just rinse them well and store them separately.
  • rock samples. I had the kids choose their own samples, but I sneakily made sure that there were some carbonate rocks in the mix.
  • safety gear, including goggles, gloves, and sleeved shirts. We used safety goggles, non-latex gloves, and long-sleeved shirts or hoodies. If I ever see a good deal, I would like to invest in lab coats, as they're the ideal protection for experiments like these, but until then... hoodies!
To set up the experiment, we removed everything from the kitchen table, covered the surface well in old newspapers, and I laid out all of the supplies to be easily accessible. Nobody is knocking over a full jar of hydrochloric acid on my watch!

Next, I lectured the children on what we would do for a hydrochloric acid spill or exposure to skin, eyes, or mouth. I lectured them until they began to look worried, and then I dwelled a little longer on emergency eye wash procedures, just for fun. There are also some good Youtube videos on lab safety, if you want someone else to worry your children. For bonus points, there's a great scene in Parks and Recreation in which one of the characters has to demonstrate how to use an eye wash station--it's super funny AND provides added incentive to be extra-safe in the lab so that you never have to experience one for yourself!

Next, we made the dilute solution of hydrochloric acid. If your kids are studying fractions, decimals, percents, and/or ratios, this is a great time to have them use them in a real-world situation. A good solution is 10% hydrochloric acid; you can translate that into fractions and decimals, and have the kid figure out how that works out into actual drops of hydrochloric acid and water. Ratios are deceptively tricky, in that a 10% solution of hydrochloric acid is NOT a ratio of 10:1 water to hydrochloric acid, right? It's 9:1! Yay, math!

The kids took turns measuring out the solution (and it was the older one who managed to slop hydrochloric acid all down the side of the bottle, sigh), and then I agitated it to mix it.

To test the rocks, all you have to do is dispense a drop of the dilute solution onto its surface and observe carefully to see if any magic happens:



And here's the magic!


There are more interesting things that you can do with this experiment, such as looking at the effervescence through a magnifier, or grinding the reactive rocks down and then dropping the solution onto them (hint: they'll be even MORE reactive!), or comparing reactions between the solution and vinegar. 

And don't worry: I already told Will that no, we will NOT be combining hydrochloric acid with bleach to make chlorine gas. Although it *would* make our trench warfare LARPing even more realistic...

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