Coin Batteries

These batteries are simply voltaic piles made by stacking alternating types of coins with filter paper soaked in saturated salt water solution. The metal compositions of pennies are sufficiently different from nickels so that these coins may be used to make weak batteries. More coins can produce more voltage, but there is a tremendous variability in the actual voltage measured. This is likely due to effects such as internal resistance and degree of corrosion on the coins.

See: Scharlin, P.; Battino, R.; Boschman, E. J. Chem. Educ. 1991, 68, 665.

ABOVE: (FIRST) A simple coin battery - a nickel on salt-water soaked filter paper on a penny. (SECOND) Measuring the potential of a single pair of coins (in millivolts). (THIRD) Measuring the potential of multiple pairs of coins (in millivolts).

Vitamin C Redox Reaction Cleans Up Iodine Stains on Hand

I learned this demo from a visitor to campus a couple years ago. This demo takes only a couple minutes. To put this together, you need to go to the local drugstore/grocery store and pick up the following:

-iodine solution (tincture of iodine, used as a disinfectant)

-spray starch

-vitamin C tablets

Step 1 - Smear some of the iodine solution on the palm of your hand. DO NOT let the iodine solution dry out (otherwise it will be hard to remove).

Step 2 - While the iodine solution is still wet, spray some starch onto the palm of your hand. The iodine spot turns blue-black as the starch molecules wrap around the iodine molecules. Again, DO NOT let this mess on your hand dry out.

Step 3 - While the iodine/starch solution is still wet, take a vitamin C tablet and rub it across the stain (I make a smiley face first). The dark stain disappears though sometimes there might still be some yellow tint left. The vitamin C tablet acts as an antioxidant, reducing the iodine to iodide ions and breaking apart the starch/iodine complex. The tablet itself stays fairly white, this it not simply rubbing the stain off, it is a chemical reaction.

CAUTIONS:

Wash your hands with soap and water as soon as you get the chance after the demo (the starch on your hand will still be sticky/slimy).

Iodine stains all sorts of things, so do not spill it.

DO NOT eat the vitamin C tablet that you used in the demo, though you should be able to use the same tablet multiple times.

You should try this demo by yourself first in case I missed any subtle details.

VARIATION: A counterfeit money marking pen, which apparently contains iodine, can be used instead of tincture of iodine. The iodine in the pen does not react with the cloth fibers in real money, but it does react with the cellulose fibers in counterfeit money. The pen can be used to draw light tinted patterns on skin, but the markings dry out fairly quickly so the starch must be applied quickly to turn them dark. These starch/iodine marks can also be erased with a vitamin C tablet.

ABOVE: (LEFT) Step 1 (MIDDLE) Step 3 and (RIGHT) Variation: Erasing counterfeit money pen marks.

Liquid Nitrogen 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).

Kylee Korte, Phuong Nguyen, and Joel Kouakou assisted in preparing this description.

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.   For a scary story about liquid nitrogen hazards, see: http://www.wpi.edu/news/19989/nitro.html.

Leidenfrost Effect with Liquid Nitrogen

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 May, 2012).

BELOW: Droplets of liquid nitrogen exhibiting the Leidenfrost effect.

 

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.   For a scary story about liquid nitrogen hazards, see: http://www.wpi.edu/news/19989/nitro.html.

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: 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.

MORE BELOW: 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.

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 has sold memory metal versions of its ICE logo.

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. We have evidence that this compound has been embedded deeply in plastic for use as thermochromic pasta and egg timers. A related compound, silver mercury iodide, is yellow at room temperature and orange at elevated temperatures.