by Dr. Kathleen A. Carrado, Argonne National Labs |
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Kids, what makes popcorn pop? This activity requires a bag of unpopped popcorn kernels divided in thirds. Two days prior, place 1/3 in a plastic container with two tablespoons of water. Put the lid on and shake the kernels so that they are all coated with water. Shake from time to time. After 2 days the corn will absorb all of the water and the kernels will appear dry. Spread 1/3 of the original kernels on a cookie sheet and have an adult partner warm them in an oven at 200° F for 2-3 hours. Keep the last 1/3 aside as your control.
Put 1 tablespoon of oil in a corn popper with 1/3 cup of the control unpopped popcorn. Listen and watch as the corn pops. Notice the condensation that forms on the inside of the popper. That condensation is proof that moisture in the seeds is responsible for the explosion. As that moisture changes into a gas, it makes the corn pop. Put the popped corn into one of 3 equal-size bowls labeled "control" or "regular popcorn."
Next pop the 1/3 roasted popcorn with 1 tablespoon of oil. First guess what will happen. Do they pop a lot more quietly? Put this popcorn into a bowl labeled "dried popcorn." Now pop 1/3 of the popcorn that has water added. You are in for a surprise! The popcorn is explosively loud, and the popped corn is fragmented and very small. Put it in a bowl labeled "water-added popcorn."
Next measure which popcorn pops best. Do this by counting 20 popped kernels of each type into a clear glass and measuring the height of the column of the popcorn with a ruler. The results should be:
What’s going on here? Popcorn is the result of an explosion. Water inside
a popcorn kernel must be heated to about 450°; F (232° C), at which
point the pressure is about 135 pounds per square inch (or 9 times atmospheric
pressure). The tough outside hull is a watertight container, keeping the steam
confined. Since the water is spread throughout the soft starch of the kernel,
the expanding steam makes tiny bubbles in the hot starch. Pent-up steam builds
up in pressure, putting more and more force on the hull until it can't take
it anymore and ruptures. This foam cools quickly to become the firm white mass
that we like to eat. Eating your results is perfectly fine – bon appétit!
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Reference:
Vicki Cobb’s book Junk Food, which is part of her "Where's the Science Here?" series published by Millbrook Press.
Kids, this is a procedure for making the non-sticky sort of rubber, or gelatinous slime, that is known as “flubber”. It is a completely safe substance that is not sticky and is non-toxic. You will need an adult partner for handling the heating steps.
Procedure:
Tip: If the flubber is sticky then the amount of water needs to be reduced. It should be clammy, but not sticky. Use less water next time.
What’s the science?
Flubber
is a polymer. Polymers are large molecules consisting of repeating identical
structural units connected by covalent chemical bonds. Polymers can be naturally
occurring or manmade. Manmade polymers are materials like nylon, polyester,
and polystyrene. Examples of naturally occurring polymers are proteins in
our body like tubulin and actin. The polymer in Metamucil is natural psyllium
fiber – a
type of polysaccharide. “Soluble” means that it will dissolve
in a lot of water, but once the water evaporates the fibers become more and
more entangled, forming our gelatinous “goo”.
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References:
Anne
Marie Helmenstine’s About.com website at: http://chemistry.about.com/cs/howtos/ht/flubber.htm and
The Science Café at http://sciencecafe.org/content/2008/12/22/make-your-own-flubber/
Kids, what kind of chemical reaction makes heat? Exothermic chemical reactions produce heat. In this reaction vinegar is used to remove the protective coating from steel wool, allowing it to rust. When the iron combines with oxygen in this chemical reaction, heat is released.
What You Need:
What You Do:
Notes:
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References: Anne Marie Helmenstine’s
About.com website at: http://chemistry.about.com/cs/howtos/ht/exothermic.htm
Kids, will a Lightstick glow longer in hot or cold weather? Many chemical reactions produce both light and heat, such as a burning candle. When a candle is lit, its flame glows and becomes hot. It is much less common for a chemical reaction to produce light without heat. The light from such reactions is called cool light, because there is no heat. Such reactions are called chemiluminescent. Fireflies produce light without heat by a natural chemiluminescent reaction. In this activity you will examine a commercial chemiluminescent chemical reaction inside a Lightstick. Lightsticks are available at many sporting goods stores, camping supply stores, and hardware stores. Amusement parks and carnivals often have them in the shape of bracelets and necklaces.
What to do:
In this activity you observed the effect of temperature on the glow of a Lightstick. Like all chemical reactions, the reaction that produces the glow is slower at lower temperatures and faster at higher temperatures. In a Lightstick, the faster the reaction is, the longer the glow lasts. When the reaction in a Lightstick occurs at a faster rate, it uses up the reactants inside more quickly than when the reaction occurs more slowly.
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References: http://scifun.chem.wisc.edu/HomeExpts/Chemilum.html
For additional information, see CHEMICAL DEMONSTRATIONS: A Handbook for
Teachers of Chemistry, Volume 1, by Bassam Z. Shakhashiri, The University of Wisconsin
Press, 2537 Daniels Street, Madison, Wisconsin 53704.
Kids, why is it that the largest nuts in a can of mixed nuts always seem to be on the top when you open the can? The “Brazil nut effect” is a phenomenon in which the largest particles end up on the surface when a granular material containing a mixture of objects of different sizes is shaken. In a typical container of mixed nuts, the largest will be Brazil nuts.
The phenomenon is also known as the muesli effect since it is seen in breakfast cereal that has pieces of different sizes but similar density, such as muesli mix. It seems counter-intuitive that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:
This effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of different sizes of granular materials is made, it is usually undesirable for them to segregate. Several factors determine the degree of the Brazil nut effect, including the sizes and densities of the particles, the pressure of any gas between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder (such as a can of nuts) works well to counter the effect, while a cone-shaped container results in what is known as the reverse Brazil nut effect.
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References: http://en.wikipedia.org/wiki/Brazil_nut_effect
This link contains a video, but it is a large file and takes a long time to download:
http://jfi.uchicago.edu/~jaeger/group/Mixed%20Nuts.html
Kids, now that summer is upon us would you like a way to prove that a sunscreen works without using your own skin as the test? For this activity you will need a sheet of black & white newspaper or construction paper (red or dark blue work best), four zip-seal sandwich bags, two sunscreens (one lotion and one spray, both labeled “clear”, and both having the same sun protection factor - SPF), a piece of fabric, and a sunny outdoor location.
Cut four pieces from the newspaper or construction paper and the fabric, sized to perfectly fit inside the plastic bags (about 5” x 6”). Place one piece of paper in each plastic bag so that the paper lies flat. Treat the bags as follows:
Seal each bag. Place the four bags in a sunny location outdoors with the treated side up. You may need to anchor them so they remain flat and don’t blow away. After 1 or 2 sunny days, open the bags to observe the paper.
The paper in the untreated bag should fade or turn yellow (newspaper) after sun exposure. But the paper samples underneath layers of sunscreen remain protected from the sun’s rays and should retain their original color. The paper under the fabric should be somewhat affected; the degree depends on the fabric used. For example the SPF of white cotton is much lower than that of denim.
Sunscreens work either by absorbing or by scattering UV rays. Sunscreens that absorb UV rays contain organic molecules, usually octinoxate and/or avobenzone. Sunscreens that scatter UV rays contain inorganic compounds such as titanium dioxide (TiO2) or zinc oxide (ZnO). The smaller the inorganic particles are, the more transparent or “clear” is this type of sunscreen.
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References: Erica Jacobsen, ACS ChemMatters, April 2010, page 15. For an explanation of sunscreen ingredients and for further activities see the same publication, page 13 by Gail Mitchell Emilsson.
Kids, how would you like to make a bio-friendly corn-based plastic that was also biodegradeable? Grab your nearest adult partner along with these materials: 1 tablespoon cornstarch, a zip-seal bag, 1 tablespoon water, 2 drops corn oil, food coloring, and a microwave oven.
Here is what you do. Place the cornstarch in the zip-seal bag. Add the water. Seal the bag and mix the ingredients well by squishing the bag with your fingers. It should look like a smooth milky liquid. Then add 2 drops each of corn oil and food coloring, seal, and mix again. The oil helps keep the bioplastic from sticking to the bag. This order of addition is very important so follow the instructions closely.
Then your adult partner performs the next steps. They will open the zip seal just a tiny bit, put the bag in a microwave oven on a paper plate, and microwave on full power for about 20-25 seconds. The bag will be very hot (caution!) so your adult partner should wait before handling. While it is still warm, but cool enough that your adult partner says you can handle it, shape the plastic into a ball.
What’s happening? Before heating, the starch and water molecules combine physically in a liquid mixture, but do not permanently attach via chemical bonds. Heating causes the water molecules to move fast enough to penetrate and break up the cornstarch granules, which then tangle together to form polymers.
Compare the biodegradable plastic you made to the plastic zip-seal bag. To watch the plastic ball degrade, immerse it in water for a few days. Compare what happens to a piece of a zip-seal bag immersed in water for the same amount of time. Because the cornstarch polymers are weaker than commercial bioplastics, they readily break apart in water. Durable commercial bioplastics need heat, microbes, and much more time to biodegrade.
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References:
C. Washam, ACS ChemMatters, April 2010, page 12; and
Field Guide to Utah Agriculture in the Classroom:
http://extension.usu.edu/AITC/teachers/elementary/fieldguides.html (Field Guide I, “Corn Starch Plastic”).
Kids, how are the north and south poles of a refrigerator magnet arranged? How are chemists able to “see” the atoms that they work with? In this activity you will discover how to answer these questions and also gain an understanding of a cutting-edge imaging technology.
A refrigerator magnet has many north and south poles, not just two as in a bar magnet. The magnetic poles are nearly always arranged in stripes. A thin probe strip cut along one side of the magnet will be deflected up and down when pulled across the back of the magnet perpendicular to the stripes. In this activity the magnetic force between the probe strip and the magnet depends on the distance between the two surfaces and the relative size and alignment of their magnetic fields. By scanning the surface with the probe, an entire surface image can be obtained. This activity is analogous to atomic force microscopy and it offers a view of magnetic force microscopy (MFM) used for larger-scale imaging.
How:
Questions:
Does the magnetic force between the probe strip and the back of the magnet depend on the distance between the two surfaces, i. e., can the probe map variations when it is far from the surface? Would the size of the tip of the probe matter? If the poles are made very small, say nanometer scale, could their arrangement still be determined? Atomic-scale images of a surface can be obtained by atomic force microscopy (AFM). To produce an image, a probe is moved relative to the surface and variations in force are recorded for a series of parallel passes. This force measurement, when plotted as a function of position, provides an image of the arrangement of atoms on a surface.
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References:
“A Refrigerator Magnet Analog of Scanning-Probe Microscopy” by Julie K. Lorenz, Joel A. Olson, Dean J. Campbell, George C. Lisensky, and Arthur B. Ellis in Journal of Chemical Education, Vol. 74 No. 9, 1032, September 1997, http://pubs.acs.org/doi/abs/10.1021/ed074p1032A.
Kids, did you ever wonder about the color of certain minerals, gems, or birthstones? Gemstones are minerals that can be polished and cut for use as an ornament or jewelry. The color of a gemstone comes from tiny, trace amounts of transition metals present in the main rock or mineral. Transition metals are those in the middle, center section of a periodic table, from scandium (Sc) to zinc (Zn) in the first row. The main rock or mineral is usually a very common material, such as silicon dioxide (silica, SiO2) or aluminum oxide (alumina, Al2O3).
Take a look at the colors of common gemstones and the metals responsible for their color. You can do this at a store that sells rocks and minerals, or a gem and mineral trade show, or even at a department store jewelry counter.
Amethyst is a colored form of quartz (silica) that gets its purple color from the presence of iron. Aquamarine is a blue variety of the mineral beryl (beryllium aluminum silicate). The pale blue color comes from iron. Emerald is another form of beryl, this time in a green color due to the presence of chromium and sometimes vanadium. Garnet is an aluminosilicate that gets its deep red color from iron. Peridot is the gemstone form of olivine, a magnesium silicate mineral formed in volcanoes. The yellow-green color comes from iron. Have you heard of Hawaii’s green peridot sand beaches?
Ruby is the name given to gemstone-quality corundum (alumina) that is pink to red in color. The color comes from the presence of trace chromium. Corundum that is any color besides red is called sapphire. Blue sapphires are colored by iron and titanium. Turquoise is an opaque mineral, meaning that it is not clear, that gets its blue to green color from copper within its aluminum phosphate matrix.
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References:
Anne Marie Helmenstine, “Gemstone Colors and Transition Metals”, http://chemistry.about.com/od/geochemistry/tp/Gemstone-Colors-And-Transition-Metals.htm?nl=1
Learn About Gemstones
Geochemistry & PetrochemistryKids, this crystal Christmas tree project works quickly from a paper or sponge tree that “grows” crystal foliage.
Make the magic solution by dissolving the salt in the water and stirring in the bluing liquid and then the ammonia. Bluing is a non-toxic and biodegradable bleaching product made of a very fine blue iron powder suspended in water (this is called a "colloidal suspension").
Here are two ways to try growing your crystal tree. You can cut a sponge into the shape of a Christmas tree, set it in a shallow dish, and pour the crystal solution over the sponge. Set the dish someplace where it won't be disturbed. You can dot the sponge with food coloring (like ornaments), if desired. Depending on the temperature and humidity, crystals may start to appear on the sponge tree in less than an hour. You should have a nice set of crystals if you let the dish sit out overnight.
Another method is to cut a cardboard or blotting paper Christmas tree. If you make two of these trees, you can cut one halfway down the top and the other halfway up from the bottom, match the notched ends together, and create a standing 3-dimensional tree. Again you can decorate your tree with food coloring ornaments, or use green coloring alone in the solution to make a solid green tree. Set this tree in a shallow dish that contains the crystal growing solution. Crystal 'leaves' will start to grow on your tree as the liquid is wicked up the paper and evaporates.
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References:
You also can get inexpensive kits to grow magic crystal Christmas trees: http://www.scientificsonline.com/magic-crystal-growing-tree.html?&cm_mmc=Mercent-_-PriceGrabber-_-NULL-_-3037475&mr:referralID=3a2a72a5-e042-11df-af68-001b2166becc
Updated 10/25/10