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.

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.

Dyeing Seashells with Blackberry Juice

Seashells can be dyed by soaking in blackberry juice. The shells below were soaked in crushed blackberries for about a half hour. Shells that have abraded surfaces tend to turn bluish. I interpret this as the exposed aragonite (calcium carbonate) having a surface with a basic pH and turning the anthocyanins in the juice blue. Some shell surfaces that are not abraded and still have a sort of a "skin" can turn reddish. I interpret this as the anthocyanins remaining at a more acidic pH as they soak into this "skin".

LEFT: Undyed shells. RIGHT: Dyed shells.

pH Sensitivity of Colorants in Flower Petals

Many compounds in plants are pH sensitive and can be used as acid/base indicators (Shakhashiri, B. Z. Chemical Demonstrations; The University of Wisconsin Press: Madison, WI, 1989; Volume 3, pp. 50-57). For example, there have been many lab experiments using red cabbage as a pH indicator. Some flowers can also be used to determine the pH of a substance, and below you will see a few examples of this. We found that pink or purple flowers showed a large color change, but yellow flowers such as daffodils and dandelions did not.

Experiment:

1. Samples were cut into small pieces and placed into three test tubes labeled H+, neutral, and OH-

2. A small amount of water was added (about 2-3mL)

3. 4-5 drops of concentrated hydrochloric acid or 50% sodium hydroxide was added and the test tube was mixed

LEFT: Quince RIGHT: Red Tulip

LEFT: Daffodil RIGHT: White Lilac

LEFT: Dandelion RIGHT: Redbud Tree

LEfT: Rhododendron (fresh) RIGHT: Rhododendron (dried for a year)

 

LEFT: Apple Blossom RIGHT: Wild Geranium

LEFT: Yellow Iris RIGHT: Purple Iris

LEFT: Purple Carnation (dyed) RIGHT: Phlox (Sweet Williams)

LEFT: Red Cabbage RIGHT: Bee Balm

LEFT: Peony (outer petal) RIGHT: Peony (inner petals)

 

Other references:

Kanda, Naoki; Asano, Takayuki; Itoh, Toshiyuki; Onoda, Makota. Preparing "Chameleon Balls" form Natural Plants: Simple Handmade pH Indicator and Teaching Material for Chemical Equilibrium, J. Chem Educ. 1995 72 1131.

Huntress, Ernest H. The Chemistry of the Red and Blue Pigments of Flowers and Fruits. J. Chem Educ. 1928 5 1392, 1615.

Geissman, T. A. Flower Coloration. J. Chem Educ. 1941 18 108.

Popcorn Rocks

When dark limestone (calcium carbonate) or dolomite (calcium magnesium carbonate) is barely submerged in vinegar (acetic acid solution) and the vinegar is allowed to slowly evaporate to dryness, white popcorn-looking crystals (calcium acetate?) grow on the surface of the rock. I have seen these rocks for sale in stores; I found mine in a park. I have seen an article (in the Journal of Chemical Education?) describing the chemistry of this process. If anyone knows the reference could you please let me know?

 

BELOW: Popcorn rock surfaces without (LEFT) and with (RIGHT) "popcorn" crystals.

Seltzer Popper Car

This is a rocket car that uses the pressure from chemical production of carbon dioxide as the basis for propulsion. The carbon dioxide is produced by reaction between acids and carbonate salts. The picture below shows a rocket car based on the popular demonstration involving water and AlkaSeltzer® in a 35 mm film canister placed on a chassis made from LEGO® parts. The "fuel" for the popping canister demonstration is approximately half an AlkaSeltzer® tablet, which is placed into a 35 mm film canister (Fuji-brand film canisters seem to work best). Water is added to the canister (to fill it approximately one third to one half full) and then the canister is capped. Ordinarily in the demonstration the canister is placed upright. The citric acid and the sodium hydrogen carbonate in the AlkaSeltzer® dissolve in the water and react to produce carbon dioxide. When pressure builds up, the cap pops a couple of meters into the air and spits out a quantity of fizzy water. The picture below shows the canister taped to a frame made of LEGO® parts. A popping canister will push a car made with this set of parts forward 10-20 cm. Other combinations of parts may produce cars that can move further. The challenge is to make a chassis that is lightweight, but with a wide wheel base to prevent tumbling. You are welcome to send alternative designs to me at campbell@bradley.edu. WARNING: The canister cap will fly backward with considerable speed, so a barrier to stop the cap is recommended. (The water will also spill out of the canister when it pops open.)

BELOW: A seltzer popper car.

Thanks to Karen Campbell for passing information about this canister demonstration from an early childhood education conference to me and to Kristine Campbell for assistance with testing the car. More demonstrations involving LEGO® bricks may be viewed at the site "Exploring the Nanoworld with LEGO® Bricks."

Lava Lamps as Demonstrations of Density, Thermal Expansion, and Surface Tension

Stacy Swanson assisted in preparing these descriptions.

A Real "Lava" Lamp
This lamp was purchased, not homemade. You can see our version of the lava lamp below.



ABOVE (LEFT): A lava lamp can take several hours to heat up the solid "lava"

(MIDDLE): After 90 minutes of heating, a few small spheres emerge. The wire coil found in the bottom of the container helps break the surface tension of descending bubbles.

(RIGHT): Three and a half hours later, the lava is fully heated. You can see the "blobs" sliding past each other, but they do not coalesce until they reach the bottom of the lamp. Without the wire coil, this lava would not coalesce to form the mesmerizing blobs we all know and love.
A Homemade "Lava" Lamp
We set out to find a perfect homemade recipe that could be used in the lab to illustrate a variety of physical and chemical properties such as convection, solubility, surface tension, thermal expansion and density. After searching the net for recipes, we tried a mixture of mineral oil (lava) and isopropyl alcohol. This gave us reasonable results, but the isopropyl alcohol evaporates quickly and with heating it evaporates even more quickly. So, we tried the mixture shown above. It is a saturated sodium chloride/water solution with silicone oil as the lava. We used iodine to tint the silicone oil purple. A 60 watt light bulb was used to heat the solution, and a wire coil from a heating element was placed in the bottom of the beaker to help break the surface tension of the silicone oil so new blobs can form. As the light bulb heats the silicone oil, the density of the oil becomes less than the salt water and the oil rises to the top. We shielded the top of the beaker from the light to keep a temperature differential so that the lava would cool and become more dense. The density of the silicone oil becomes greater than the salt water and the silicone oil sinks. When picking ingredients, the densities need to be similar, and the coefficient of thermal expansion for the lava should be high relative to the surrounding liquid. Ideally, the mixture should be placed in a sealed container to prevent evaporation. Another homemade recipie and a bit of lava lamp history can be found at: http://www.oozinggoo.com/
BELOW: A homemade lava lamp.


More history of lava lamps can be found at:
www.straightdope.com/classics/a2_359.html
www.uspto.gov/patft/index.html (you can see the original US patent (#3387396) through this search engine)
More lava lamp links can be found at:
http://www.lavalites.com/
http://www.lavaworld.com/
http://www.mathmos.co.uk/