ChemShorts for Kids -- 2002
Copyright ^©2002 by the Chicago Section of the American Chemical Society

by Dr. Kathleen A. Carrado, Argonne National Labs
kcarrado@anl.gov

ChemShorts Home

January, 2002 Icy Explorations
Kids, let's try to take advantage of the cold weather here in the Midwest. You know that a backyard pond or lake in winter can be a magical place. It is also filled with many scientific wonders. These bodies of water freeze from the top down, and they do so for two reasons. The top is closer to the cold air for one, but mostly it's because water has the amazing property of getting lighter as it freezes. That's why ice floats. In liquid water, the H₂O molecules can pack together very tightly and randomly (without a regular structure). In ice, the molecules form hexagonal (six-sided) crystals, like a tiny honeycomb. This arrangement forces the molecules farther apart than in liquid, which is why ice is less dense and therefore lighter than water. The ice crystals are so dominant that they work hard to force out gases and impurities. If you look at the edge of a pond that is solidly frozen, you should see clear ice with some trapped bubbles. The ice might look dark, even black, but that is the dark water underneath. You might see plant life and even fish (like perch) underneath. They'll all look magnified because of the ice.

Try this way to visualize the internal crystal structure of the ice. Buy two polarizing filter sheets from a science supply or hobby store. These are similar to what is used in sunglasses to block certain wavelengths of light. On a cold day, look for puddles on your street or in your yard that have formed a skin of ice. Pick up a piece of the ice and press it between the two polarizing sheets. This part is important - make sure the two sheets are at right angles to each other. Now hold the "ice sandwich" up to the light and observe.

Have you heard grinding noises at the edge of a frozen lake? It's from expansion and contraction of the ice along cracks and fractures formed between different layers. You need AT LEAST four inches of solid ice to walk on, so don't walk onto a frozen lake or pond until an adult has measured the thickness. Despite the grinding noises, ice can be incredibly strong. In some places lakes freeze over a foot thick, which is enough for small vehicles. While strong, ice is also flexible. No vehicle can go faster than 10-20 mph over ice, because waves can form in the flexible ice sheet and this stress can break it apart.

Here's a fun fact. You know that polar bears live on ice and snow, and that they are white, right? Wrong. A polar bear's fur is actually made up of transparent, hollow hairs. Each hair works like a tiny fiber optic tube, and channels the sun's heat to the bear's black skin, helping it to stay warm. The clear hair reflects light, just like ice and snow, which makes them all appear white. This is all "cool" stuff, isn't it?

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Reference: Tom Connor and Martin Jeffries, Scientific American Explorations magazine (www.explorations.org), Winter 2002, p. 28.
P.S. Check out an exhibit called "Animals of the Ice Age" through 5/20/02 at the SciTech Museum in Aurora, IL.

February, 2002

Penny Popper

Kids, this column is for you really young ones, ages 5-7 or so. It is about something called surface tension. We will concentrate on water here, because water molecules really like to stick together. An electrostatic-like force attracts them. When they are near each other, they will try very hard to stay together instead of going off on their own. Even though individual molecules are too small to see, you can see how they work by watching their behavior.

Note to your adult partners: manipulating materials and equipment are important experiences for young children. In addition, using words to describe observations helps to develop mental muscles. To do this have them answer questions like "How?" "Why?" and "What makes you think so?" throughout this activity.

First, practice using a medicine dropper by slowly releasing water one drop at a time and counting drop by drop. To an adult partner, predict how many drops of water you can drop onto a penny before the water runs off. (Most children will guess between 2 and 10 drops). If more than one of you are doing this activity, make it a competition to see who can get the most drops on the penny.

Now it's time to start and test your prediction. Add drops one at a time. We'll bet that you'll be surprised how many the total can be (adults – see below). Look at the water on the penny's surface as it builds up higher. Describe its shape. The reason why so much water can be held there is due to surface tension. Water molecules hold tightly to one another on all sides. At the surface, the molecules don't have any neighbors above them to hold onto. So all of their holding power is used on molecules on their sides and below. That makes the surface act like a strong skin that can hold in a lot of the molecules.

Try the activity again but first add a drop of dish soap to the water. The penny will hold fewer soapy drops, and the dome will be flatter. Detergent molecules lessen the "pull" between water molecules. Interestingly, a chemical word for soap that helps to describe this action is "surfactant".

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Reference: Faith Brynie, "Water's Molecular Madness" in Scientific American Explorations magazine, Winter 2002, page 34. Most children are excited to see the total amount go to 20 drops or more on the penny.

March, 2002

Soda Science

Kids, here you'll be dabbling in the science of drinkable bubbles by making your very own root beer soda pop. Most sodas use pressurized carbon dioxide for the bubbles, but that would be very difficult to mimic at home. So instead we'll be using yeast to carbonate the brew. Last year we discussed the use of yeast in baking bread (12/00-2/01). The scientific process is called fermentation, where yeast eats sugar and makes carbon dioxide and alcohol by-products. (It's only a little alcohol here: an entire 2-liter bottle of root beer has less of it than is in one really ripe banana!).

What you'll need is a scrupulously clean and dry 2-liter plastic bottle and cap (sterilized is best), active dry yeast packets, tepid tap water, sugar, and root beer or vanilla flavoring. Wash your hands and all utensils very thoroughly. Fill a 2-cup glass measuring cup with tepid (room temperature to warm) tap water. Dissolve one tablespoon of sugar in the water. Add 1/8 teaspoon of yeast to the sugar water. Stir gently and let stand 5 minutes. This is called "proofing", and you are proving that the yeast is still alive. In a 2-quart glass bowl combine 6 cups warm water, 1 cup sugar, and 1 tablespoon root beer flavoring. Stir thoroughly. If the yeast has a thin layer of froth (tiny bubbles) on top, it can be added to the bowl now. (If your yeast had no froth, try slightly cooler or warmer water, or buy a new supply). Stir thoroughly and pour the mixture into the bottle. Add more water until the liquid reaches about one inch below the bottle's neck. Cap, and let the bottle stand at room temperature for 2-4 days. You'll know it's ready when enough CO₂ has formed to expand the bottle and make it feel rigid, like it was just bought at the store. Now refrigerate for at least 2 days to stop the growth of the yeast. After this you can drink your very own soda. It is best consumed within one month.

People used to make soft drinks at home this way all the time using wild yeast, long before commercial brands were available. People still use wild yeast today to make sourdough bread starter. Root beer extract can be found now in large grocery stores near vanilla and other extracts in the spice aisle. In later batches, try to change the taste a little by changing from sugar to other sweeteners like brown sugar, honey, or molasses. Enjoy!

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Reference: Beth Robelia, "Root Beer Chemistry" in Scientific American Explorations magazine, Winter 2002, page 12.

April, 2002

Heat Packs and Supercooling

Kids, there is a cool (okay, not really) product available on the market for a reusable heat pack/handwarmer that is loaded with chemistry-in-action ability. It's called a "Zap Pac Heat Pack" (contact info below). While a monetary investment is required, it dramatically and safely showcases the phenomena of both supercooling and an exothermic reaction.

These products consist of a concentrated aqueous salt solution together with a flexible metallic activator strip (usually stainless steel) in a sealed, flexible container. Sodium acetate and calcium nitrate are examples of suitable salts (Zap Pacs use the former). These salts are much more soluble in hot water than in cold water. The flexible metal strip is bent back and forth a few times, whereupon a white cloud of crystals begins to precipitate. Within seconds, the entire pack is filled up with solid crystalline needles of sodium acetate without any solution left, and the temperature raises to 130°F for about 30 minutes. Because heat is released upon this precipitation, it is called an exothermic reaction (the opposite is called an endothermic reaction).

Supercooled liquids can be cooled below their normal freezing point without turning solid. Then, at the flick of button, the supercooled liquid is triggered to solidify (crystallize) and at the same time release large amounts of heat. Salt solutions that have been processed in such a way that their temperature can be lowered well below their solidification (or melting) temperature and still remain in liquid are defined as supercooled or metastable liquids. The triggering device initiates the rapid solidification of the solution. In the case of salt solutions that release or absorb large amounts of energy during phase changes (common table salt sodium chloride does not do this), the solidification process is a rapid crystallization that releases large amount of heat at the salt solution's normal melting temperature.

The activator is a thin metal piece with ridges and a specially roughened surface. The flexing causes metal-to-metal contact that releases one or more very tiny particles of metal from the roughened surface. This acts as a nesting site for one crystal deposited from the solution and (voila!) all of the crystals fall out instantly.

These heat packs are reusable because, by re-heating the pack in boiling water for a few minutes, the salt re-dissolves and the pack again contains a clear solution. (Be sure to have an adult partner help you with this part). Best of all, the activator strip can be reused dozens of times!

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Reference: Prism Enterprises, Inc., P.O. Box 680728, San Antonio, TX 78268, (210) 520-8051 (www.heatandcomfort.com). See C. Manker's U.S. patent #4,872,442 and also www.pcm-solutions.com/superc.html for more insight. Thanks to Joe Gregar for telling us about this product.

May, 2002

Lightening with Lemons

Kids, how much do you know about lemons? Here is a very quick and easy test of the power of lemon juice. Have an adult partner make a mug of hot tea for you from a teabag. Use a white or clear mug so that you can easily see the color of the tea. Now take a fresh lemon wedge and squirt in a few drops of the juice. Upon stirring, certain kinds of tea will instantly lighten up considerably, "magically", right before your eyes. In some cases this works so well that you can make a magic trick out of it. Squirt the lemon juice into a spoon first, out of sight, and then stir it in the tea to watch the color change. Try different types of teabags to see which work best. I have found that the best are the so-called "black" teas (see "Chemistry in a Teabag" from this column in October 1998), such as: regular Lipton tea, Superior orange pekoe & pekoe cut black tea, and Pickwick English Blend traditional black tea.

What appears to be happening is a type of mild bleaching process. In fact, the vitamin C (ascorbic acid) in lemons is known to be a bleach (see another one of our columns, "Clearly it's Vitamin C" from October 1999). Bleaching is the process of removing the natural color of something (cloth, paper, wood, food, etc.). Chemists call the processes either "oxidizing" or "reducing". Vitamin C is an organic compound, which means that it contains carbon, hydrogen, and oxygen (the formula is actually C₆H₈O₆). It happens to oxidize very easily, which means that it is a good reducing agent. Tannins or other highly colored organic molecules in the tea are reduced when the ascorbic acid is oxidized.

If you were to stain a white cotton rag with some black tea and let it dry, you could try to remove it by spotting with lemon juice and letting it dry in the sun before washing. This might also work if tea were to accidentally stain a t-shirt, tablecloth, or linen napkin.

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Reference: Check http://library.thinkquest.org/27034 for all kinds of bleaching.

June, 2002

Chalky Chromatography

Kids, do you think you can unmix your favorite marker color? Some of the bright colors in your watercolor marker set are not made from a single pigment. Rather, just the right amount of different pigments is often mixed together. You can unmix, or separate, all of these pigments using a process called chromatography. This is one way that chemists use to separate mixtures into their individual parts. We have talked about chromatography previously in this column (see columns on the web from 10/92 and 2/95), but we have never asked chalk to do the work for us before.

You'll need watercolor markers (several different colors and brands, be sure to try black), water, long fat pieces of white sidewalk chalk, and clear cups. Fill a cup with 1/4 inch of water. Using a marker, draw a line of color around a piece of chalk, about 1/2 inch from the bottom. Stand the chalk in the water with the color line just above the water line. Don't let the water line touch the color line otherwise the color will just wash into to the water. Instead, what you want is for the water to percolate up the chalk. It will then dissolve the ink pigments and carry them up the stalk of chalk. Different colors of pigment will travel up the chalk at different rates, depending on the size, shape, weight, and composition of the pigment molecules.

Eventually the chalk will be decorated with a colorful, smeared-out band. Let it dry out and then use this designer chalk to decorate your sidewalks and driveways. Try it again with new pieces of chalk and other colors.

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Reference: Joan Silberlicht Epstein, Scientific American Explorations magazine, Spring 2001, page 45.

September, 2002

A Potato Power Plant

Kids, this activity uses a common potato and two different metals to make enough electricity to run a small digital clock. Try this activity then attempt to expand on it to make a science fair project. You'll need a large raw potato, 2 pennies, 2 large galvanized nails, 3 pieces of 6" long wire, and a small digital clock (such as a Radio Shack Stick-on Timer for $4.99). The digital clock can be taken from an inexpensive alarm clock or it can be purchased from an electronics store.

First cut the potato in half and place the halves next to each other flat face down on a plate. Strip off about 2 inches of insulation from both ends of each wire. Wrap one end of one wire around one of the nails. Press the nail into one of the potato halves. Wrap one end of another wire around one of the pennies. (Do this by laying the penny across the exposed wire, positioned so that it is centered on the wire and almost touching where the insulation begins. Fold the end of the exposed wire over the top of the penny. Pinch the penny and wire between your index finger and thumb on one hand and pinch the overlapping wire with the other hand. Twist the penny until the wire tightens around the penny). Press the edge of the penny about half way into the other half of the potato. Attach one end of the third wire to the second nail and the other end to the second penny as before. Insert this nail into the potato that already has the penny stuck into it then stick the penny into the potato that already has the nail stuck into it. Pop the back off the timer/clock and remove the button battery. Connect the two wires coming from the potato battery to the contact on the battery holder. If the clock does not light then the polarity (+ / -) might be incorrect. Just touch the wires to the opposite contacts on the timer's battery holder in that case.

How does it work? Here's the chemistry - the potato contains phosphoric acid. This acid causes chemical reactions to occur at each of the electrodes (galvanized nail and copper penny). The reaction at the copper electrode strips electrons from the copper metal. The galvanized nail contains the zinc needed for the other reaction. The phosphoric acid dissolves the zinc in the nail, which also strips electrons from the zinc. The resulting zinc ions (Zn⁺⁺) migrate into the acidic juices of the potato. This results in an excess of electrons on the zinc electrode. When a wire is connected from the zinc nail to the copper penny, electrons will flow. This flow of electrons is the electrical current that makes the digital clock function. After this, try hooking the potato battery to an oscilloscope to measure a voltage (about 0.5V); several potato batteries could be connected in series to increase the voltage.

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Reference: www.quantumscientific.com/pclock.html

October, 2002

Cookie Coal Mining

Kids, there are many things that we use every day that are mined from the ground. Things you may never think of such as portland cement which is used to make concrete, or sulfur, or salt, are mined. Illinois mines provide primarily crushed stone, portland cement, sand, gravel, and coal. The website www.msha.gov/kids/mining.htm will let you click on any state to see what is mined there. Coal is our most abundant fossil fuel resource. It is a complex mixture of organic chemical substances containing carbon, hydrogen, and oxygen, with small amounts of nitrogen and sulfur. The degree of coalification, also called the rank of coal, increases from lignite (brown coal) to low rank coal (sub-bituminous), to high rank coal (bituminous), to anthracite. Carbon goes up and oxygen and hydrogen go down along the series. The hardness increases and the reactivity decreases. Different heats and pressures during geochemical development cause these differences in rank. It is not due to the kind of plants the coal is formed from.

U.S. coals range from lignite with 30% carbon and a heating value of 7,000 Btu per pound to anthracite with 85% carbon and a heating value of 12,750 Btu per pound. Sub-bituminous and bituminous coals are between these values. There are two methods of mining coal, surface mining and underground mining. There are over 1,000 mines of each type in the U.S. Underground mining is more difficult and requires more miners, but much of our best coal is underground. Lately, surface mining in Wyoming has made it the top coal producer at almost 300,000 tons per year. West Virginia and Kentucky, the traditional leaders, each produce around 170,000 tons. Last year about 1 billions tons of coal was mined in the U.S. with almost 60% used by electric utility companies. Coal is also used to make plastic and steel. When used as a fuel, coal can be burned just as it comes from the ground or converted into fuel liquids.

Here is your activity. Get a chocolate chip cookie, a chocolate chunk cookie, an oatmeal raisin cookie, and two toothpicks. Think about how these cookies represent mining the 3 major types of coal. The raisins represent the soft coal lignite, the chocolate chips are the hardest coal anthracite, and the slightly softer chocolate chunks are most like bituminous coal. All of them are embedded in cookie dough "rock". Using your toothpicks as jackhammers and picks, separate the coal from the rock. Make neat piles of chips, chunks, raisins, and cookie crumbs. Now put the cookie crumbs back together. How, and why, you say? Reclamation is an important part of the mining process in order to be good stewards of the land. Some stone quarries that are now recreation areas are Centennial Beach in Naperville and Quarry Beach in Batavia. (By the way, don't forget to eat the fruits of your labor!).

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Reference: www.osmre.gov, and J. Licandro (Scullen Middle School, Naperville) from 8/4/02 "School Rocks" article in the Naperville Sun by D. DeFalco.

November, 2002