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.
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Comments 6
The beauty of chemistry
The videos and those of golden rain are indeed beautiful. Here is Declan Fleming showing you golden rain, http://www.rsc.org/eic/2014/12/golden-rain-precipitation-demonstration
However, how many of you in the States are allowed to use lead compounds in your classes. One can use lead in the UK but precipitates should be collected, dried and stored for correct disposal by a licensed contractor. However, in some countries of the EU, the very use is prohibited.
But why is lead iodide yellow? I see that silver iodide exhibits a yellow colour as well.
All the best
Bob Worley
A nice variation!
Hi Bob,
Thanks for sharing the golden rain variation. Quite nice!
As for the use in the U.S., that's a great question. Before I moved overseas, I was allowed to use it as a demo, but not directly with students. I also had to keep a bottle in the back for waste disposal that my county helped with as needed. Quite sound practice, in my mind.
I have often wondered about the color. I'm sure there are others that have a better answer than I have at this point.
Andy Brunning - of Compound Interest fame - has a great graphic on the Golden Rain demo you highlighted here as well.
Regards,
Beautiful, indeed
Well done, Lowell and students. Did I really see the precipitate "bounce" off the bottom of the flask?! This is truly a fascinating result!
We saw the same bounce
Hi Tom,
Thanks for that. I've always enjoyed the spontaneous ideas that come during and after class. I saw the same bounce, and that it was quite interesting. I didn't have enough spare time that day to do more investigating. It's on my list for after IB exams!
Beautiful Chemistry
Beautiful Chemistry was inspired by the influential art nouveau illustrations in German biologist Ernst Haeckel’s 1899 portfolio of prints Art Forms in Nature, which helped the public at large visualize microscopic and marine life. http://www.beautifulchemistry.net/“We hope to follow the footsteps of Haeckel, using digital media and technology to bring the beauty and wonder from the chemistry world to a wide audience,” the Beautiful Chemistry team writes on its website. “We want to achieve a unique aesthetic of chemistry, making chemistry approachable.
Beautiful chemistry, indeed!
Thanks for sharing that side. I'll be passing that along to my students as well.