The Exploding Pumpkin Demo

Here's my version of the Exploding Pumpkin Demo.

 http://www.youtube.com/user/sgeyer68?feature=mhee#p/a/u/0/h2Yqjr9595g

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

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.

Making Water

The base is in the 1-L volumetric flask.

Adding the acid to the base

More than 1 liter here!

Shakhashiri has all the answers.  I like to do the demonstration of a neutralization reaction with equal volumes of hydrochloric acid and sodium hydroxide.  The reaction produces salt and water.  If you mix 500 milliliters of 2-molar solutions of the acid and base, you will produce 18 mL of water (1 mole).  I learned about this demo at ChemEd, a great conference for chemistry teachers.  In previous years, I used a 1-liter graduated cylinder, my favorite demonstration glassware, for this reaction.  Although it always worked, the additional volume of water was very difficult to see.  Shakhashiri has a description of this same demo in volume 3, Demo 9.17, with the solution to my problem.  He uses volumetric flasks!  Of course!  Today, when I combined the 500 mL of acid and base, both made up in 500 mL volumetric flasks, the additional water was easily visible in the neck of a 1-liter volumetric flask.  I added some universal indicator to the acid and base solutions to give the demo some color.  This was an extra bonus because the two solutions formed layers when I poured them together the 1-Liter flask.  We all enjoyed the interesting effect of the blue and pink layers.  When I mixed the flask, the volume increase caused pressure to build up in the flask and the stopper popped off a couple of times.  Overall, the Demo was a great way to show the products of a neutralization reaction, including the often-overlooked water molecules that are formed.

 

Releasing the pressure.

Admiring the interesting layers.

The “Mini Grain Elevator” Demo

Take a look at this one!

I have wanted to do this demo ever since my second year of teaching.  I have read the instructions many times, found in Volume 1, Demo 1.41 of Shakhashiri’s Chemical Demonstrations.  Every time I have read them, I would think, “I’ve got to try this, but it seems scary.”  The set-up always gave me pause.   I put it off until I “had more time”; just another excuse to delay plunging into this experiment.

The Flinn Kit

At the end of last year I was looking through the Flinn catalog for my summer supply order.  The kit for the Mini Grain Elevator caught my eye.  I decided to get the kit and give it a try; surely a kit would be easier and the experts at Flinn have tested it.   I was still too scared to do it by myself, so I dragged my ever-willing colleague into the fun.  We set up the quart sized paint can with a pipette full of lycopodium powder. Just light the candle, secure the lid of the can with a hammer, and then squeeze the pipette into the sealed paint can.  Simple, right?  The instructions for the kit say, “Stand back as far as possible as you squeeze the pipette.”  This didn’t put us at ease. On the first try we got a big bang, the lid flew off, it was exciting.  But the pipette rig was not reproducible.  Attempts two and three were duds, nothing happened and the candle went out.  I decided to go back to “the bible” and, with the support and enthusiasm of my colleague, together we spent the afternoon building our Mini Grain elevator rig.

Here are a few pictures from the construction of our Mini Grain Elevator.   We bent a funnel for the inside of the can, punched a hole in the paint can, scrounged around the science building for a rubber bulb, and put the whole thing together in a 1 gallon paint can.

This rig was awesome.  It made a loud explosion, the lid flew off the can, flames shot out of the top of the can, and the candle flew out of the can.  Attempts two and three were equally impressive.  Making the rig was worth the effort! My colleague and I spent a couple of days setting off the Mini Grain Elevator for all of our classes and for any other visitors to the lab.   It was really fun every time we ignited the can.  The physics guys next door and the biology teacher down the hall came in to watch it go off several times too!  My husband even made the trek from the next building to watch the famous Mini Grain Elevator explode.  My reputation as a closet pyro was confirmed with this demo.

Bending the stem of the funnel.

Second attempt.  We broke the first funnel.

I used my awl to make a hole in the paint can.

A look at the inside of the can.

Attaching the funnel to the can.

Loading the lycopodium powder.

Demo Show for Pack 26

 

This week I gave a demo show for my sons’ Cub Scout Pack. 

Pouring carbon dioxide onto a candle.

I started off the show with the Genie in a Bottle trick, a ChemFax by Flinn Scientific (Publication No. 91200).  I wrapped a 2-liter plastic bottle in aluminum foil to make the Genie’s bottle.  The “Genie” was a reaction of 30% hydrogen peroxide and sodium iodide, the catalyst in the decomposition reaction of hydrogen peroxide that produces water and heat.  The sodium iodide crystals were suspended in a small sack at the top of the bottle held in place by a rubber stopper.  When I took the stopper off the bottle, the Genie escaped in a big puff of steam, and left behind a shrunken plastic bottle. 

For my second demo, I asked one of the Tiger Cubs to come up and fill up a beaker with Styrofoam packing peanuts.  The peanuts “disappeared” as fast as he could put them into the beaker.  I encouraged him to try harder, but the peanuts kept shrinking before his eyes.  What he didn’t know is that I had poured some acetone, a clear and colorless organic solvent, into the beaker before the show.  The small amount of acetone quickly dissolved the packing peanuts as he dropped them in the beaker.

 

 Blue water for displacement.

Next I did a water displacement demonstration with baking soda and vinegar, one of the many reactions that produce carbon dioxide gas.  I like doing this demo for kids because it’s a different look at the classic “volcano reaction”.  Taking the advice of Dr. Shakhashiri, I used large apparatus to make the reaction visible to the audience.  I collected the gas in a 2-liter bottle, using a 5-gallon fish tank for the water displacement.  I had a volunteer mark the water level on the tank before the reaction so we could see any change.  I put food coloring in the water in the bottle so there was another visible change for the kids to observe during the demo.  Once we filled the bottle with carbon dioxide gas, I used it to put out a candle.  I love to show kids that gases can pour, even when we can’t see them.

Heating the water in the can.

Ready to flip it into the ice water bath.

The finale was the classic “Can Crushing Demo”.  I heated a small amount of water in an empty soda can until steam was visible.  I quickly inverted the can in an ice water bath.  The can crushed with a shocking smash.   I learned how to do this demo during my summer workshop at Longwood College.  I was hooked on chemistry demos after performing this one for my class that fall.

 

The can crushed in the ice water.

 

Thanks to Pack 26 for inviting me for a fun night of science.

Oooo That Smell…

This sign was posted by my physics colleague today.

I really don’t try to make my colleagues hate me, I swear.   

Today we did the classic Iron and Sulfur experiment.  This is a full assault to the senses, most notable the olfactory.  In this experiment we compare the physical properties of iron, sulfur, and a mixture of iron and sulfur.  Then we put the mixture in a test tube and heat it vigorously, which causes a chemical reaction between the two elements. 

The iron and sulfur reaction is very exciting to watch.

The reaction takes a few minutes to get going.  At first, the reaction mixture smolders a bit; some of the sulfur comes off as a gas, and condenses on the sides of the test tube as a red and yellow coating.  Then a red glow begins to form in the test tube, which spreads until it looks like lava inside the test tube.  It actually produces enough heat to sustain the molten-looking reaction for several seconds without the Bunsen burner flame.  

Notice the puff of sulfur coming out of the test tube.

Plunging the test tube in water is all part of the fun.

 For the finale, the students plunge the test tube into cold water.  The reaction mixture gives off a big puff of steam, accompanied by a loud hissing sound, and some of the water boils around the black product pellet.  The hot glass cracks, releasing their sample of iron sulfide into the beaker of water.  At this point, everyone in the room is too excited about the flames, the molten product, and the breaking glass to notice the strong sulfur smell.  Of course, the students in the neighboring physics and biology labs are not amused when the odor works it way throughout the building.  

 Sorry guys, but this one is totally worth it!


 

A Visit with Dr. Shakhashiri

What a thrill to meet Dr. Shakhashiri again!

I’m still giddy from meeting Dr. Shakhashiri again after all these years.  I am so thrilled to have had the chance to thank him for changing my life.  Okay that sounds really dramatic, but it’s true.  Without that workshop at Longwood College in the summer after my first year of teaching, I would have quit teaching chemistry.

Dr. Shakhashiri is dropping dry ice into these 1-liter grads.

Today I enjoyed another inspiring demonstration show from Dr. Shakhashiri at the 100^th year celebration of the Connecticut Valley Section (CVS) of the ACS.  You can see where my love of the 1-liter graduated cylinder originated!  After every demonstration he performed, I turned to my colleague and said “We’re totally doing that one this year!”

 Watching Dr. Shakhashiri perform his demos is not a passive activity.  He engages every member of the audience with a steady stream of questions.  At the beginning of the talk Shakhashiri said, “Chemistry is the science of the familiar”.  He reinforces this statement with his demonstrations by relating the chemistry to everyday experiences.  He is a master at drawing out all the chemistry that his audience already knows but they didn’t know was chemistry.

Dr. Shakhashiri pours boiling water over dry ice to make fog.

Today feels like the right moment to tell the story of my second year of teaching.  I returned to my school in rural Virginia armed with new ideas and filled with determination to “do it right” this time.  I opened the year with an exploding hydrogen balloon on the first day.  My students were excited to come to class on day two.  I implemented a new micro scale lab curriculum in my classes, another part of the workshop at Longwood.  I tried some new classroom management techniques that I learned from long conversations with the other experienced teachers at the workshop.  I maintained contact with several of these teachers my second year to help me through the rough spots.  It was a completely different experience; I fell in love with teaching that year.  

Check out Dr. Shakhashiri's website.

 http://scifun.chem.wisc.edu/