Tuesday, December 13, 2011


Thanks to my good friend and fellow science teacher, Josh, who makes the high speed videos.
Who doesn’t love the thermite reaction?  This reaction is exciting, dramatic, and a bit scary.  Shakhashiri describes it like this, “Flame, flying sparks, smoke, and dust are produced.  Molten iron runs through the hole in the pot into the sand bath.”  I pulled out this demo today as part of the “5-types of chemical reactions” unit and a great example of an exothermic reaction.  Thermite is a single displacement reaction with a high activation energy.  The thermite mixture, aluminum powder and iron oxide, can sit on the shelf quietly without much concern because it takes another reaction to get it started. 

Inserting the ignition stick into the thermite mixture.
I tried to use the potassium permanganate reaction with glycerin (as described by Shakhashiri) to get the reaction going.  I did the potassium permanganate reaction yesterday in class, so it seemed like a nice follow up today.  (By the way, it filled up the room with smoke and we all poured out of the classroom coughing as the bell rang at the end the period.  I’ll do it outside next time!) The permanganate reacted vigorously with the glycerin, but it did not produce enough heat to spark the thermite.  (You can watch this “dud” reaction at the end of the “Thermite Balls” video.)

Take a look at the chunk of iron that we collected from the water bath.
A close-up of the iron drops that formed from the reaction.
So I went back to the stand-by:  thermite ignition sticks that we bought from the chemical supply company.  These sticks are essentially really fat sparklers.  I used a Bunsen burner to light the stick, and then I ran outside with my burning sparkler.  I held it in the thermite mixture until the reaction started.  Once it got going, all that was left to do was stand back and enjoy the show.  Watch for the molten iron dropping out of the bottom of the clay pot, making the water in the tank boil.  I fished out the iron pellet from the tank to show the kids the iron drops that formed.  

I followed up the thermite reaction with what I call “hand held thermite” or “thermite balls”.  I can make the same reaction on a smaller scale with two rusty cannon balls, one covered with aluminum foil.  With enough activation energy, provided by hitting the balls together at a high speed, sparks fly and there’s a loud pop.  The high speed video doesn’t do justice to the reaction without the sound effects, but you get to see the classic facial expressions I make when I do the demo.  I never realized how much I flip my hair until I started this blog project.

Ready for the hand held thermite reaction.

Tuesday, December 6, 2011

The Exploding Pumpkin Demo

Here's my version of the Exploding Pumpkin Demo.


Thanks to my friends who inspired me to try this demo by posting a video of a another chemistry teacher doing this on my facebook page.  My version is a small scale, "cute", look at the reaction of calcium carbide and water.  The mixture produces acetylene gas, which is flammable.  The pumpkin gets filled with the acetylene gas, if you wait long enough, and makes a nice explosion.  This demo was a good way to say goodbye to Halloween

Monday, December 5, 2011

Heat of Dilution of Sulfuric Acid

Measuring heat of solution.

My thoughtful students are contemplating their data.
Calorimetry is not exactly a flashy subject.  Heat exchange into and out of water does not make for a showy demo.  However, today I did a demo for my honors class of the heat of dilution of concentrated sulfuric acid, Demo 1.6 in volume 1.  To my surprise, this demo offered an element of excitement that I was not expecting (why am I surprised that the demos from Shakhashiri are exciting?).  I decided to run three trials at the same time, dissolving 10, 20, and 30 mL of concentrated sulfuric acid in 100mL of water.  I used one of my Lab Quests from Vernier with 3 temperature probes so we could watch the temperature readings graphically projected on the big screen.  I asked for three volunteers; the hands went up immediately.  Three boys came up to pour in the acid and help monitor the reactions.  I counted to three and then they all poured at the same time.  The exciting part was the 30 mL sample, which produced enough heat to boil the water and overflow out of the cup all over the bench.  It was a surprise to us all to see this happen.  The spike in the temperature readings told the whole story of the heat produced from diluting sulfuric acid in water.  (Do as you "oughter", add acid to water.)  We followed up with the calculation of the heat produced in each cup, which led to the conclusion that this is a linear relationship.  The demo ended with me pouring baking soda onto the spilled acid, producing the classic “volcano” reaction on the bench.  Welcome to calorimetry, kids.

"What, no flames today?"

Taking his temperature with the Vernier probe.