Co-op Science Week 18

Chapter 2 of ACS Inquiry in Action

This week we tried to identify a mystery crystal.

We started off by giving the students 4 knowns:  sugar, salt, MSG, and Epsom salts.  I had written those 4 names in silver marker on the corners of half-sheets of black construction paper, which I handed out.  I also wrote the chemical formula for each on the board, and gave a bit of commentary.  I'm trying to get them used to seeing things like "NaCl" -- Thalia said that she absorbed an amazing amount through the years from just being exposed to us mentioning various concepts in the course of conversation.


For example, I told them I thought "maybe sodium was Na because that was short for 'natrum', which is what the Egyptians used to mummify -- hey, did any of you ever mummify a chicken? (blank stares from class) Really?  I thought that was a standard homeschool thing to do for history ...." etc.  In other words, the random prattle my kids have been subjected to for years, which has apparently worked as an introductory course in Random Stuff.

We handed out copies of the first activity sheet so they could follow along with the reading, and answer questions or draw pictures as they desired.

We also handed out magnifying glasses.  Our co-op has a bunch of plastic ones, so I have no tips on where to find cheap ones, although I'll note that CVS struck me as fairly expensive.  The salt, sugar and Epsom salts I had around the house (one girls was eager to share that they used Epsom salt to remove a stinger when her brother had a bee sting).  I used to have a little container of Accent (MSG) but had thrown it out years ago -- I wasn't even sure it was still sold -- does anyone actually USE this stuff?  But I found some at Target, along with a box of the unknown, which was kosher salt.  And the other mom and I walked around distributing small piles of the various crystals on their construction paper.

The kids really liked using the magnifying glasses on the crystals.  A few thought the mystery crystal was sea salt.  I asked how sure they were, and moved on to the next activity -- the hardness test.

(Although one boy was pretty sure we should try to identify the unknown by feeding all of the crystals to fish -- I assumed he was talking about doing an LD50, although there IS an aquarium in the room, so who knows what was going through his head.)

We talked a little about controlling the experiment -- how will you know that you're treating each crystal the same, without variability?  Really a pretty decent discussion -- the kids seemed really engaged in the necessity to think like scientists. I think this might've been the point at which I reminded them that Galileo just made do with the equipment he had centuries ago -- he didn't have the uber-accurate digital clocks, so he measured his pulse to gauge time (I'd brought this up last fall in class).  We distributed plastic spoons, and set them loose crushing crystals, recording their observations on the appropriate handout if they so chose.

Finally, the solubility test.  I gave a quick rundown on why we measure by weight rather than volume (this was outlined in the ACS handouts -- I used Rice Chex for my demo, and a bucket balance we had at home [probably for elementary math, although I really don't recall why we have it] -- as usual, the kids liked the part where I pounded the Rice Chex into little bits, although they were quite argumentative about whether we had the EXACT SAME AMOUNT afterwards).  I also drew a quick graph on how the amount of sugar that will go into solution varies by temperature, while salt pretty much remains the same -- this was also in the ACS material -- I asked the class if they were used to reading graphs, and again got the blank stares, but forged ahead based on the above-mentioned theory that they should be exposed to new concepts even if they don't know exactly what I'm talking about.

Also, when I'd looked up the chemical formula for MSG I noticed that the wikipedia article gives all sorts of standard info for it, which I showed them on the iPad.  Things like the melting point, the LD50 ("Oral, for rats.", "but why do they use rats?   Rats are really cool!",  "I know -- we have pet rats -- that's just what they often use for those experiments.") and solubility -- scientists have figured out this stuff and have this info around in charts to help them figure out new stuff.  Pretty clever, eh?

I demonstrated how to do salt and sugar -- dissolving them in hot water (I had taken hot water in a Thermos), swirling in plastic cups while the other mom counted out 20 seconds on her watch.  Then we formed 3 groups, I measured out the weight equivalent of 10 paper clips worth of each substance using the bucket balance so each group had samples of all 5 (salt, sugar, MSG, Epsom salt, unknown) which we put in tiny Dixie cups, handed out plastic cups, and had each group organize themselves.  The other mom counted out the seconds for everyone en masse while they slowly swirled their cups.  It was really a pretty cool experiment, and we discussed how the different things dissolved.

The final activity per the ACS curriculum involved re-crystalizing the water that had just been poured off of the crystals.  I knew we wouldn't have time for that in class, so I had done it at home the day before, and took the plastic cups of crystals in to show the kids.

And, in the end, the kids who guessed sea salt were pretty close in knowing what the mystery crystal was.  I really liked the more creative guesses, though, like Splenda and white sand -- I sort of suspect the kids who said "sea salt" just figured out how most of these demos-for-kids work ("okay, they won't have anything TOO weird for us to figure out") while the outliers will do better in a real lab some day.

Really, we barely had time to get through all of these activities in an hour, plus do a little clean up of the water we'd spilled on the tables.  I think we're going to slow down the pace a bit, since I feel like we're rushing through all of this helter-skelter.

I think the kids are learning a lot about how scientists work, though.  As I said, they seem really engaged in the process.  No clue if they're actually learning any chemistry.