Co-op Science Week 21

Inquiry in Action chapter 4 -- Dissolving Solids and Liquids (we'll get to gases next week)

Activity 1 is to simply dissolve sugar and food coloring in water and in vegetable oil.  I did this as a class demo -- had some of the kids do it while everyone watched.  Then we discussed how we define dissolving.

Rick thought I should also talk about emulsions by mixing oil and water together.  I thought this might be confusing (I mean, there's a reason the ACS didn't include it in this chapter, right?) but then I decided what the heck -- I dumped some water plus food coloring in a bottle, followed by some vegetable oil.  Shook the whole thing up while talking about it, babbling away about emulsifiers, how lecithin in egg yolk acts as an emulsifier and hence we can make mayonnaise, blah blah blah .  The kids were FASCINATED.  They acted like they'd never seen this sort of thing before.  I kept asking, "Haven't you ever made salad dressing?"  They demanded we pass around the bottle so they could look at it.  I put in a couple of drops of Dawn dish detergent to show how it would change our mixture -- again, they acted like they'd never seen anything like this before.  All in all, a very eye-opening experience for me.

Next we made colored sugar.  I had them pair up, and handed out ziplocks with pre-measured tablespoons of sugar.  The adults went around the class and put a drop of food coloring in the bag, which the kids then shook up (I had tried this at home to make sure it worked).  Bonus math lesson -- how many teaspoons are in a tablespoon?  Three!  Each pair then got 3 plastic cups already labelled for oil, water, and alcohol, plus popsicle sticks (purchased at the Dollar Store, by the way).  Adults measured out the liquids, and we also helped them measure the teaspoonfuls of colored sugar into each cup.  The latter was done mostly to speed things up since we didn't have enough teaspoons for every pair to have their own.

Next we skipped ahead to activity 4, dissolving liquids in water.  Again the kids worked in pairs, and were handed 3 plastic cups which had already been marked for oil, alcohol, and corn syrup.  The kids filled the cups partway with water (we have access to pitchers which we can fill at sinks).  Adults handed out small Dixie cups with the required alcohol, oil, and corn syrup (note: when measuring out the corn syrup it helps if you put a bit of oil on the tablespoon first).

The kids were amazingly intrigued by this activity.  One boy who typically has very little attention span was excited by the way the alcohol dissolved in the water -- "It looks like veins!"  Last week we had combined drops of alcohol and water, then discussed that the refraction rates caused the jiggly effect, so it was interesting that he was so excited about this.  The BIG news, though, was what happens when you put a tablespoon of oil in a cup of water.  It sinks to the bottom, then bounces back up ... then coalesced into a giant blob of oil on the top ... which you could sort of blop around by squeezing the cup.  It was as though no one had ever sat around playing with oil and water before (when my kids were little I put oil and colored water in old plastic water bottles and let them play with it -- either these kids never did that, or they were so bored by not having much to look at in the classroom that they really paid attention for the first time).

I had taken coffee filters, washable markers, and Sharpies for a follow-up activity, planning to show how you can make designs depending on whether you use water or alcohol to dissolve the markers (you can also do faux tie-dye with Sharpies and alcohol on cotton tshirts).  But we ran out of time, so I just mentioned it as a possible follow up at home.

Overall, I thought this was a sort of blah lesson.  But the kids worked well together on it, so it was good from that standpoint.