Co-op Science Week 20

Continuing Chapter 3 of Inquiry in Action

This week we tried Using Color to See How Liquids Combine, and Using the Combining Test to Identify Unknown Liquids.  I thought theses were pretty fun experiments when I did them at home beforehand.

To combine the liquids in an orderly fashion, I printed out the templates provided onto cardstock.  The directions suggest laminating them or putting them in a plastic bag.  I don't own a laminator, but was fairly certain the plastic bag concept would drive me nuts because the plastic would slip around the cardstock.  I considered using wide clear packing tape, which I'm pretty sure would work well to stick over the parts of the template that need to be waterproof.  But I found some Xyron Glossy Laminate Sheets  (which are sort of like 9 inch by 12 inch sheets of transparent Contact paper) at JoAnn, and used my 40-percent-off coupon on that.  You can also laminate at a place like FedEx/Kinko's, although that would've cost more than what I spent on my Xyron sheets.

After that, it was a matter of mixing up the appropriate batches of detergent water, salt water, isopropyl alcohol, and plain water with some food coloring.  I put these in my little Solo condiment containers (purchased last week at Walmart), and used my eyedroppers from last week.

The idea of the experiment is that you eyedropper blue-colored water onto one circle on the template, then eyedropper yellow liquid onto the other circle nearby.  A toothpick is used to "herd" the one drop towards the other.  Once they touch, you observe what happens.

And let me tell you, I found what happened amazingly cool.  Okay, the water and detergent water weren't all that amazing -- I could picture what was going to happen.  But the  yellow salt water plus  blue water?  They suddenly smacked together like neodymium magnets, forming a green droplet ... but that droplet had a funky striated appearance when you looked from the side.  So I used the eyedropper to gently suck the top off the drop ... and SUCKED THE BLUE RIGHT OFF THE DROP!  Yes, the plain water stays on top, and doesn't actually mix with the salt water (Rick, Mr. ChemE, found this an exciting proof of the strength of the bond between NaCL and H2O; I just thought it was a cool thing to mess with, like a magic trick).

Then the blue water plus the yellow alcohol met ... and started to shimmer and shake like green jello.  Very cool.  That has to do with the refraction of the light passing through the air vs. water vs. alcohol, a concept we covered last semester during our physics portion of class.

So, to do this in a co-op class, here are some tips:

First of all, it really really helps to have an adult (or older student) per group of kids.  This is tricky business -- they're having to eyedropper liquids onto circles (and keep paper towels nearby so if they mess up they can just wipe off the laminated cards and start over) and then gently move the drops together without actually using the toothpicks to stir the 2 liquids (which sometimes happened by accident).  Also, not to be sexist, but a lot of time girls this age have steadier fine motor skills than boys, so it's nice to have mixed groups.

I transported all of my liquids to the class via old plastic water bottles, which I labelled with Sharpie.  You'll need enough for knowns and unknowns.  We just capped up the condiment containers and threw them in the trash when we were done.  I wonder if I should've taken them home to wash out -- we might need more of them for later experiments.

We instructed the kids to lay their eyedroppers on paper towels when not in use.  For the most part they managed to do this, which cut down on some of the spills.

And, yes, you'll need 9 eyedroppers or pipettes per group do conduct these 2 experiments.

Some of the kids caught on to the value of replicating experiments -- it was really cool to see them working these things out.  They're learning a lot about how science is "done" by working through this curriculum.  Overall, some of the kids are absolutely loving this, and others don't seem to be terribly engaged; I'm pretty sure this is normal.

The 2 experiments took about 45 to 50 minutes of our hour long class.  The groups work at amazingly different rates, with varying amounts of arguing about how they should proceed and who gets to do what.  In the future I'm going to have some other related demos or activities to fill in the rest of the time.