I was late to the party. Like really late. I just did the blue glitter intermolecular force demo for the first time. I know, it’s the best thing and it’s been around forever. I just haven’t used it. I will highlight a few of the tips that I learned by trying this new demo. As a disclaimer, I am not much of a demo guy. At all. I love labs. I love challenging students in their thinking. I just don’t do demos to do that. Many demos are more like magic tricks. They get an Ooooo and and Ahhhhh but then don’t connect deeply to the content. Blue glitter demo has some of that, but I think there is enough content there to repeat it. Here are some tips for completing the blue glitter intermolecular force demo.
Use more blue glitter than you think.
In some of the instruction videos I watched, they said to use a small amount of glitter because the dye readily comes off the glitter (I used the glitter from Walmart as seen above). In my attempts (before I did it with the class), using a small amount of glitter didn’t do much. The blue acetone just wasn’t that blue. I did the demo in a test tube. I used a 100 mL beaker to prepare the acetone solution. I added about 10 mL of glitter and 50 mL of acetone. That made an intense blue relatively nonpolar solution.
Cover the acetone solution.
I know, I’m dumb. I just forgot about it and left my beaker of acetone solution over night uncovered. And shockingly, a relatively nonpolar solvent has lower intermolecular forces and evaporated before the morning. Maybe I should pay attention to my own class. If you are saving it, cover it.
Ask questions as you go through the demo.
I set up the acetone/glitter beaker as well as a small beaker of glitter and water to demonstrate that the blue dye is not soluble in water. Then I put about 1/3 of a test tube full of blue acetone in the test tube. Add 1/3 of a test tube of water. Since acetone and water are miscible, the blue dye spreads throughout the test tube. Asking questions about why the dye was mixing with the water brough up some good thoughts. We looked at the molecular structures and talked about how molecules can have varying levels of polarity. I had a beaker of water and dropped a drop of yellow food coloring in it. I asked questions about the intermolecular forces present in that dye. Then I put an image of yellow and blue dye on the board and had the kids figure out which was which based off the interactions. This line of questioning was valuable.
Blue dye molecule
Yellow dye molecule
Use more salt than you think.
I added a drop of yellow food coloring to the test tube with the acetone/water/blue dye. It turns green. This is another good spot to ask questions. Then, to separate the dyes, the instructions that I found said to add salt. So, I added what felt like a good amount, and shook it. Nothing. So, I tried it again. Nothing. Finally, I started adding what felt like a ton of salt. I finally got a good separation. I was pouring salt into the test tube until it was about ¾” deep at the bottom. I understand Ksp and why this shouldn’t be necessary, but in practice, this is how I got it working.
Shake more than you think.
In the videos I watched, the demonstrators did not show how much you actually need to shake the solution to get quick separation. In one class, I thought I had the system down and it failed. I set it down to talk more, hoping it would separate. It didn’t. So as a last-ditch effort, I almost sarcastically shook it a really long time. And wouldn’t you know, I got separation of the dyes. Quickly. When in doubt, shake it longer.
Don’t do it as a lab.
As I said before, I am much more prone to do a lab than a demo. I was considering making this into a lab. But I will not. Mostly because of glitter. I got it everywhere, and I am a relatively responsible adult. I also don’t want to deal with large amounts of acetone waste. The benefits of this demo were appropriate to spend 10 minutes of class time but not valuable enough for a 50-minute class or a 90-minute block. It’s a functional demo. Not a lab for me.
Enjoy it.
There is something satisfying, even for an old chemistry teacher, in watching colors separate. Enjoy it. Let the kids enjoy it. And then press them to understand it. Don’t let it stop at the level of a magic trick. Challenge them to communicate at a high level what is happening. Then you too, can become part of the blue glitter chemistry clue. You will recognize us by the blue glitter under our fingernails. And in our hair. And on the floor. And…
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