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."