Kids totally know that oil and water don’t mix. But getting them to understand how usually involves drawing Lewis Structures. What’s weird, is that when I moved and started teaching in a new state, my kids didn’t need to know how to draw Lewis structures, but needed to know like dissolves like. (But they do need to know VSEPR Theory, so overall, kinda weird…) So, I was given the new challenge of trying to figure out how to effectively teach them. Of course, I gave them an intro to Lewis Structures, but our course pacing is SO FAST that there’s really little time to explore outside the bounds of the curriculum. And truly, I find Lewis structures pretty boring, so the less time I spending teaching it, the happier I am.
Even when I had to teach Lewis structures, I found that this lab activity worked really well for teaching like dissolves like. If you’re looking for a lab rubric to help your students communicate their findings, sign up here and get a copy sent to your inbox.
Like Dissolves Like Lab Activity
I usually set this up as stations, for ease of setup and cleanup. I give my students test tubes, water and a bunch of different substances. Then they will add a few drops of each substance in order to determine if it is polar or nonpolar. I usually do this to have my students evaluate the Lewis structure. But for this lab, it’s really just to get them to investigate polar and nonpolar.
The substances in this hands on activity for teaching likes dissolves like are usually found in a kitchen. I’ve done a few different versions of this lab and different substances each time. Here’s a list of things I’ve used:
- food coloring
- rubbing alcohol
- baby oil
- mineral oil
- corn oil
- olive oil
- vinegar
- milk
- orange juice
- hydrochloric acid
- liquid soap
- vanilla extract
- soy sauce
In all honesty, it doesn’t matter so much what chemicals you choose to complete the lab. Especially if you aren’t so much focused on the Lewis Structure. As long as you have a decent mix of polar and nonpolar substances, you can really get away with choosing whatever substances you have available to you. I started out teaching chemistry in a retired art classroom, so my collection of lab activities are usually low maintenance.
Knowing that water is polar, it’s easy for students to determine what other chemicals in the mix are also polar. You can even have the students mix together two or three (non-reacting) nonpolar substances to really test the hypothesis.
Mind Blowing Trick
Now here’s a doozy. I actually made a home-made always dry sand. I put the sand in a disposable aluminum tray because the chemicals are really stinky. Then I put some decorative sand in the tray and spray it with this waterproofing camping spray. I do a little bit of stir, spray, stir spray until I feel like I’ve sprayed all the sand. You can see the color deepen from the spray, so it’s decently easy to tell. Around 24 hours later, I will check on the sand and test it in some water. The best part about this strategy is that as the sand loses it’s waterproof qualities, you can spray it some more. It took me around 10 uses to need to redo the sand. Read detailed instructions on how to make the sand here.
The sand should be able to mix with water and become wet, but when it doesn’t the students now have a question to answer. Why doesn’t the sand mix well with water like it should? How can this sand come out dry? You could get really crazy and give them two samples of sand – one that is waterproofed, and the other in its natural state. This always leads to awesome class discussions. I’ll tell you, this hands on like dissolves like activity is one my students rarely forget.
