Capturing the Beauty of Chemistry with an iPad

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.

 

 

Join the conversation.

Comments 6

Bob Worley's picture
Bob Worley | Mon, 02/22/2016 - 16:57

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

Lowell Thomson's picture
Lowell Thomson | Mon, 03/14/2016 - 07:31

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.

- of fame - has a great you highlighted here as well. 

Regards,

Tom Kuntzleman's picture
Tom Kuntzleman | Tue, 03/08/2016 - 20:02

Well done, Lowell and students. Did I really see the precipitate "bounce" off the bottom of the flask?! This is truly a fascinating result!

Lowell Thomson's picture
Lowell Thomson | Mon, 03/14/2016 - 07:33

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!

 

Jaquan Alan | Thu, 03/10/2016 - 04:42

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