In my IB Chemistry class, my seniors were finishing up independent investigations for their Internal Assessment a few weeks ago when something cool happened. One of my students was using silver nitrate and potassium chromate for a titration. This is notable to the story here because the endpoint is marked by the formation of silver chromate as a precipitate, with a deep reddish color. I overhead the student showing his reaction to another student, with both of them commenting on the cool colors involved.
For some reason it got me thinking about one of my favorite reactions: potassium iodide with lead II nitrate. It's a simple double replacement reaction, forming lead II iodide precipitate, which has a vivid yellow color. I've always enjoyed combining two clear, colorless solutions and producing this solid yellow precipitate as a simple demonstration.
I mentioned this reaction to the student, and he couldn't remember if I'd shown the class the demo or not. To be fair, it would have been at least a year ago, buried within reactions and the rest of Topic 1: Stoichiometric Relationships. So the student and I set about to film the reaction just to take a closer look. Here's some video of our attempts at filming:
I'm sure you can find better videos online with high speed cameras looking at the reaction in slow motion. This was just filmed in the classroom - on an iPad - without much thought to background beyond using whiteboards. As you can see from the video, we played around a bit with the best way to film the reaction. Using a dropper ended up being our favorite, and raising the height of the dropper created some really cool effects as well.
I've often wanted to create videos of some of my favorite reactions so I could create a library of reactions to share with students. And for some reason, this conversation with my student sparked that curiosity in both of us to look at ways to capture the beauty of this reaction. I think I'd like to capture the single replacement reaction between zinc and copper sulfate next.
Do you have any videos of reactions you'd like to share? What is your favorite reaction to demo? I'd love more ideas for the next time a student is interested in filming a reaction.