My goal is to incorporate as many relevant demonstrations into the classroom as possible. Here are photographs of some demonstrations that I have done. Caution: The descriptions of these potentially dangerous demonstrations are incomplete. If you have questions about these demonstrations or suggestions please contact me at campbell@bradley.edu.

Spontaneous Assembly (or "Self Assembly") of Hot Dog Slices

Cut hot dogs into ~1 cm thick slices and place them in a pan of water. They will float at the water's surface and attractive capillary interactions will draw them together into an organized close-packed array.

References:

Dungey, K. E. J. Chem. Educ. 2000, 77, 618.

Campbell, D. J.; Freidinger, E. R.; Hastings, J. M.; Querns, M. K. "Spontaneous Assembly of Soda Straws." J. Chem. Educ., 2002, 79, 201.

Campbell, D. J.; Freidinger, E. R.; Querns, M. K. "Spontaneous Assembly of Magnetic LEGO® Bricks." The Chemical Educator, 2001, 6, 321.

Campbell, D. J.; Freidinger, E. R.; Hastings, J. M.; Querns, M. K. "Spontaneous Assembly of LEGO®s." Chem13 News, Sept., 2001, 8.

 

ABOVE LEFT: Cutting hot dogs into slices. ABOVE RIGHT: Floating them in a pan of water. Note: sometimes tapping the pan will help shake out some of the defects in the assembled pattern.

 

Thermochromic Battery Tester (thermochromic leucodye film)

The built-in battery testers on common alkaline batteries are based on films of thermochromic inks called leucodyes. When the test "buttons" on the battery are pushed, a current from the battery flows past the leucodye film, heating it slightly and causing it to lose its color. To check this, I cut the battery tester off an Energizer® "D" cell with a razor blade. At room temperature the film appears dark, but body heat can change the leucodye layer to colorless, exposing a green background layer that provides contrast so the black-lettered word "GOOD" may be read. The Energizer® and Duracell® battery testers checked by Robert Bailey changed color at roughly 40 C.

 

References:

White, M. A.; LeBlanc, M. "Thermochromism in Commercial Products" J. Chem. Educ., 1999, 76, 1201.

Viiri, J.; Kettunen, L. "Temperature Profile of the Duracell® Test Strip" Phys. Teach., 1996, 34, 276.

Clark, R. W.; Bomicamp, J. M. "Tapered Resistors" Phys. Teach., 1995, 33, 340.

 

BELOW LEFT: The battery tester at room temperature.

BELOW RIGHT: The battery tester in contact with a metal cup of hot water as a source of heat.

Copper Mercury Iodide (thermochromic powder)

The synthesis and properties of this inorganic solid is described in Ellis et al. "Teaching General Chemisty: A Materials Science Companion." The material undergoes a phase transition from a red solid at room temperature to a dark brown solid above ~55 C. This is due to enhanced ion mobility in the high-temperature phase. When the synthesis is complete, the dry powder may be smeared onto heavy paper and then laminated with transparent tape or contact paper. This provides a means of handling the material without coming into direct contact with the mercury compound. The entire demonstration card may be heated with a heat gun or a hot plate to illustrate the phase change.

ABOVE LEFT: A Solid State Model of the low-temperature phase of copper mercury iodide.

ABOVE RIGHT: Smearing copper mercury iodide on heavy paper. Note the use of gloves and goggles.

BELOW LEFT: The demonstration card at room temperature.

BELOW RIGHT: The left side of the demostration card on a hot plate. Note the darkening of the powder.

Special thanks to Dr. David Shaw at the Madison Area Technical College for providing the pictures.

 

Memory metal (solid-solid phase change)

>>> bend >>>>>> apply heat >>>

 

ABOVE: Nitinol or "memory metal" as it is called is a nickel-titanium alloy that may be "trained" to remember its shape. If the proper kind of memory metal is trained to a particular shape in its low temperature or martensite phase (left) and is then bent out of shape (middle), then gently heating the metal with a heat gun or hot water to its high temperature or austenite phase will restore the metal to its trained shape (right). Training the metal involves heating it to a much higher temperature, such as that of a candle flame.

 

To train a piece of wire, bend it to the desired angle outside of a candle flame. Then hold onto the wire tightly and place the desired bend point into the candle flame. Since the material is a metal it will conduct heat, so you may find that holding the wire with gloves or pliers is desireable. The wire will initially try to straighten out as it heats up, but if you hold the wire tightly it will then soften at the point of the wire in the flame, creating a nice, tight bend. The hot, bent wire may be cooled in water. The Institute for Chemical Education sells memory metal versions of its ICE logo.

 

Homemade Shrinky Dinks®

Transparent polystyrene packaging such as those used to hold baked goods can be used to make plastic trinkets. (Not all clear packaging works. Polystyrene containers should have a number 6 inside the recycling triangle on the plastic.) When the plastic is heated, stretched-out polymer chains have enough energy to relax their orientations. As a result, thin flexible sheets of the clear polystyrene will shrink laterally, thicken, and become less flexible. Writing that was placed on the surface of the polystyrene with permanent markers will also shrink. This polymer behavior is the basis for Shrinky Dinks®, a craft/toy that was popular in the 1970s and 1980s, and can still be purchased today.

 

®Shrinky Dinks is the Registered Trademark of K & B Innovations, Inc.

 

ABOVE: The polystyrene "windows" on envelopes can be used to make Shrinky Dinks®. Before (LEFT) and after (RIGHT).

BELOW: Patterned polystyrene sheets before (LEFT) and after (RIGHT) being placed in an oven. Use a relatively low temperature (about 65 C) or they will melt rather than shrink! NOTE: Many but not all sheets of polystyrene will shrink and not all sheets will shrink equally in all lateral directions.

BELOW LEFT: Making clear polystyrene icicles. There is a significant burn risk here. A polystyrene sheet placed on aluminum foil in a toaster oven at 300 F or simply to "toast" mode will shrink fairly quickly (it is fun to watch - but don't leave them in the oven too long or they might melt). A narrow triangle of polystyrene container material, with a hole punched in the top, is shown at LEFT. The wrinkles usually flatten out upon heating. While the shrunken sheets are still hot, remove them from the oven, twist them quickly into a spiral shape, and hold until they have cooled, as shown at RIGHT. If the shape of the twist is unsatisfactory, placing the icicle back into the oven will untwist it. Again, there is a significant burn risk here. My wife loaned me her thimble to provide a measure of protection.

BELOW RIGHT: One can make interesting faces on polystyrene sheets, shrink them, and attach them to pom-poms. (Hot melt glue works much better than school glue for this.) Placing a magnet on the back enables the decoration to stick to a refrigerator door. The picture below includes a couple versions of moles (a popular mascot for chemists) and a tomato cartoon character that is popular in the Campbell household.

 

 

 

 

Liquid Nitrogen Demonstrations

Kylee Korte, Phuong Nguyen, and Joel Kouakou assisted in preparing these descriptions.

 

CAUTION: Liquid nitrogen is very cold and presents a serious frostbite hazard, especially if it gets trapped against your skin (e.g.in your clothing). Additionally, gaseous nitrogen occupies more volume than the same quantity of liquid nitrogen. Gaseous nitrogen produced quickly enough in sufficient quantities can displace oxygen from the air. Containers filled with liquid nitrogen could fail without warning due to thermal shock or gas pressure. Protect yourself accordingly.

 

Leidenfrost Effect

Named after Johann Gottlob Leidenfrost, a German doctor, the Leidenfrost Effect is an occurrence where a liquid comes in contact with a material that is much hotter than its boiling point and creates a vapor layer to prevent it from further direct contact with the material. The liquid then boils much more slowly as it is protected by the insulating vapor layer. Liquid nitrogen on a smooth surface at room temperature can illustrate this phenomenon. The liquid nitrogen is obviously the liquid and the surface is the material that is much hotter than it. Droplets of the liquid nitrogen will move easily across the surface, supported on cushions of nitrogen vapor.

Reference:

Wikipedia: Leidenfrost effect. http://en.wikipedia.org/wiki/Leidenfrost_effect (accessed June, 2006).

BELOW: Droplets of liquid nitrogen exhibiting the Leidenfrost effect.

 

(

Geysers

A geyser is a steam and water eruption (spring) water coming into contact with a very intense underground heat source. Certain geysers are periodic, but most of them occur in periods that vary from seconds to hours. For a geyser to occur there has to be heated rock underground, an abundant source of water, and a "plumbing" system consisting of channels in the ground that conduct water to and up away from the heated rock. Water flowing into the plumbing system is heated many degrees over its boiling point. Eventually the pressure of the heated water increases to the point that water and steam will be rapidly ejected into the air. Eventually, the plumbing system will restock itself with water and repeat the process again.
Liquid nitrogen geysers have been observed on Neptune's moon Triton (these are believed to erupt via a different mechanism than here on Earth). A small liquid nitrogen geyser can be made by placing a meter-long copper tube partially into a pool of liquid nitrogen. The tube at room temperature is inserted into the Dewar flask that contains some liquid nitrogen. Since the boiling point of liquid nitrogen is 77K and the tube is approximately room temperature (298 K), liquid nitrogen entering the tube will quickly vaporize, pushing vapor and liquid nitrogen up the tube into the air for a brief time.

Reference:

Wikipedia: Geyser. http://en.wikipedia.org/wiki/Geyser (accessed June, 2006).

BELOW: A liquid nitrogen geyser. The copper tube shown here is 120 cm long with an inner diameter of 1.4 cm.

 

Base Surges and Downbursts

Base surges and downbursts occur when dense gases sink rapidly down through less dense gases and spread outward upon impacting the ground. Base surges are clouds of gas and dust that move along the ground away from a volcanic eruption or a nuclear explosion. It is often produced when a column of these clouds collapses to the ground. Downbursts, and smaller microbursts, occur when cold air sinks to the ground from a thunderstorm. A similar phenomenon seems to occur during the filling of a typical 4 liter Dewar flask with a relatively narrow neck from a liquid nitrogen supply line. As the liquid nitrogen (boiling at 77 K) first passes through the supply line and into the flask at room temperature (about 298 K), the liquid nitrogen flashes into pressurized vapor. The vapor rushes out of the Dewar flask, creating a column of cool nitrogen vapor and condensed water droplets. As the supply line cools, liquid nitrogen actually makes it into the Dewar flask. The liquid nitrogen boils away less rapidly and the pressure forcing the nitrogen vapor up from the Dewar flask decreases. The cold dense vapor column then collapses down and spreads across the ground, resembling a base surge or a downburst.

References:

Clark Johnson. Base Surge. http://www.geology.wisc.edu/~g111/Terms/base_surge/base_surge.htm (accessed June, 2006).

Denton County, Texas. Downbursts. http://www.co.denton.tx.us/dept/main.asp?Parent=82&Link=84#Mistaken (accessed June, 2006).

 

BELOW: A liquid nitrogen base surge: (LEFT) Formation of the column of cool nitrogen vapor and condensed water and (RIGHT) collapse of the column.

 

 

Soap Suds Explosion

I saw this demonstration on the "David Letterman Show" and just had to try it. It simply involves quickly pouring liquid nitrogen (WARNING: Extremely COLD!) into hot water (WARNING: HOT!) containing dishsoap. The liquid nitrogen flashes to nitrogen gas, causing a large explosion of rather cool soap suds. This demonstration is best done outside since so many suds are produced. An awesome demonstration of phase changes!

 

BELOW LEFT: The soap suds explosion.

BELOW RIGHT: Aftermath of the soap suds exposion. I got suds all over me from this one (note the suds on the step rails and on the ground).

 

 

Demonstration Pictures: Page 1, Page 2, Page 3, Page 4, Page 5, Page 6, Page 7

 

Link to pictures of LEGO demonstrations

Return to Dr. Campbell's Favorite Demonstrations

Last updated6/10/06

Site created at the laboratory of Dean Campbell