ChemShorts for Kids   --   2000
Copyright ^©2000 by the Chicago Section of the American Chemical Society

We urge you to visit a fantastic crayon empire called The Crayola Factory in Easton, PA (610-515-8000) where you can watch crayons being made. The paraffin is delivered to them in heated tanker-train cars and stored in two-story silos. When needed, the wax is pumped into large, heated kettles and mixed with pigment. This crayon mixture is pumped into a rotary mold machine that has thousands of crayon shaped holes, and chilled with cold water. An Instron testing device is used to check the barrel and tip strength of crayons because a strong crayon is a better crayon (sometimes kids grab crayons by the handful or press too hard when they draw or color).

All Crayolas contain the same amount of paraffin wax blend. But their density depends on the amount of color pigments added. Therefore, some crayons will float in water while others will not, and some will sink faster than others. Find out for yourself by performing your own experiments (although we won¹t be responsible for actually telling you to dump your whole box of 96 colors into a bathtub?). No one is saying what pigments are really used because that information is top secret. Some examples for reds might be ocher (an iron oxide mineral), carmine (from an insect), or madder (from a plant). All we can be sure of is that several different pigments are used and that they are all non-toxic. If you are interested in recycling, can you think of a way to re-use your broken crayons instead of throwing them away? One thing to try, with the help of an adult, is to put all the broken pieces into an empty soup can and put this into a shallow pan of water on the stove. The adult can then heat the water enough to melt the crayons, and pour the warm wax into a new mold of some type.

Place your index card the long way (vertically) on a table with the blank side up. With each of three magic pens, draw parallel, horizontal lines about 2 inches long and about 1/4 inch wide, separated by about half an inch or so. Add a fourth line by bunching up the red cabbage leaf and rubbing it until you see a streak of color on the card. Using the white color-change wand, draw a straight, vertical line (perpendicular), that crosses all four color lines. Label it "wand". Now pour a little bit of water, vinegar, and baking soda solution into three separate plastic cups. Using new cotton swabs for each solution, dip in and "draw" the wet swabs across all four color lines as before, labeling each one.

Describe and compare the effects that the wand, water, acid (vinegar) and base (baking soda) solutions have on all of the colored lines. Are the pens sensitive to acids or bases? Here is one example of using the pens: draw a line with the color-change wand first, then draw across it perpendicularly with a blue marker. It¹ll be blue on either side of the wand path, but a different color (turquoise), where it crosses the path. The low pH color (blue) is observed where there is no base (ink from wand), and the high pH color of turquoise appears on the base¹s path. (Remember, high pH means basic and low pH means acidic).

Here is the chemistry behind the "magic". Like many pens, the ink used here is composed of many parts. The magic pen ink contains deionized water, glycol as a humectant (substance that retains moisture), a non-sudsy detergent (to help spread liquid on a surface), citric acid (the acid in lemons and orange juice) to create a low pH, and a dye. The color-change wand contains water, glycol, and detergent, as well as a base (such as sodium hydroxide), and a reducing agent (such as sodium sulfite). Because of the base, it¹s pH is about 10-12 depending on the brand.

Let¹s see how it works in braces. The bracket part of braces is a tiny metallic or porcelain anchor glued to a tooth. As many as 12-14 of these minihandles are fastened in each jaw. Next a thin flexible Nitinol wire is fastened to each bracket and bent back and forth as necessary to connect the misplaced teeth. This special wire is elastic (actually, "superelastic") and wants to, very slowly, return back to its original straight shape. Moving at about one millimeter per month, the wire brings the teeth with it. Eventually, a stronger stiffer wire is needed to move teeth into their permanent final alignment, and orthodontists often use stainless steel for this. Both Nitinol and stainless steel (an alloy of iron and carbon with some chromium and nickel) are resistant to acids and corrosion. You never see rust on braces even though they are in a wet environment and exposed to weak acids (citric acid, decomposition of sugars, etc.).

Another example of Nitinol¹s properties is in the springs of eyeglass frames whose arms can flex slightly out, away from the body, without damage. One of the most amazing demonstrations of shape memory is when it is temperature dependent. Nitinol can do this as well. A straight wire can be wound into a tight coil, put into hot water, and instantly it springs back to its straight shape. Eyeglasses with this Nitinol in the temple piece can be squashed or severely bent, but restored by immersing in hot water. This effect is caused by a change in the crystal form of the metal. It transforms between the high temperature phase called austenite and the low temperature form called martensite. Because the phase change occurs with just a simple shearing motion of the atoms, and no diffusion or large atomic movement is required, the transformation occurs virtually instantly and can cycle many times.

What are the active ingredients in toothpaste? There is fluoride of course, either as sodium fluoride or sodium monofluorophosphate. Fluoride reverses the process of tooth decay where acids (especially from sugar) dissolve minerals right out of the teeth. There are antibacterial agents such as triclosan to control plaque and antitartar agents to control mineralized plaque. Other, inactive or inert, ingredients are water, detergents (to loosen plaque), binders (keeps solid and liquid ingredients together), humectants (to keep it moist in the tube), flavoring, preservatives (to stop bacteria from growing on the other stuff), and abrasives (for cleaning and polishing).

Using the tests that follow, you will use inquiry to observe, collect data, and make informed decisions related to consumer choices. You'll need toothpicks, 4-5 brands of toothpaste, a toothbrush, and also a microscope would be great. Prepare a chart listing the brands of toothpaste with sections for texture by "touch", "taste", and "microscope". Rub a bit of each brand between your fingers and note whether it feels smooth, gritty, etc. Then brush your teeth with each brand and record the texture by taste. Next, using a toothpick, smear some toothpaste on a microscope slide, add a drop of water, and put on a coverslip. View the slide in a microscope and draw a picture on your chart of what it looks like. Now compare all the brands for texture, grit, and appearance. Which would you choose, and why? Why is this better than just using water to brush your teeth?

What do you suppose the abrasives are? This grit is often silica, alumina, calcium carbonate or sodium bicarbonate. Chemists are able to make toothpaste clean, polish, and protect your teeth, plus make it taste good and sit up on your toothbrush, too!
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References:

October, 2000

Kids, chemistry is so common that it can even be found in money. Here we'll learn some science about coins and bills. Let's talk about coins first. Pennies obviously look different by their color while all the rest appear to be the same silvery color, until the new 2000 "golden" Sacagawea dollar coin came along. Have you ever thought about what metals are used to mint these coins? All the silvery-looking coins are actually made out of copper with small amounts of nickel. This nickel amount can be as low as 8% (dimes, quarters, and half dollars) to as much as 25% (nickels). Makes sense that the most is used for the nickel, right? The new gold dollar is really made of "manganese-brass", which is 88% copper, 6% zinc, 4% manganese, and 2% nickel. The penny has seen quite a few changes over the years. It was pure copper way back in 1793-1837. For the next 20 years, it was bronze (95% copper, 5% tin+zinc). Then even this small amount of tin was removed in 1962. In 1982, pennies became copper-plated zinc coins, with a thin coating of Cu (2.5%) over a pure zinc core.

Have you noticed that some coins have grooved edges? Dimes, quarters, half-dollars, and dollars used to contain precious metals like gold and silver. Grooved edges helped stop counterfeiting. It also stopped the filing down of edges by people who were collecting (actually stealing) the precious metals. Even though coins no longer have such metals, grooved edges are kept because they help the visually impaired to identify them. The chemical element symbols for all of these coinage metals are: copper (Cu), nickel (Ni), manganese (Mn), zinc (Zn), tin (Sn), gold (Au), silver (Ag).

Did you know that "paper" money is actually made of 1/4 linen and 3/4 cotton? This makes it more like fabric than paper and explains why it's washable. There are many counterfeiting-fighting features used, especially on the new "big head" bills, but we'll mention only a few here. You notice of course that the portraits are enlarged and off-center. This allows for a watermark, which is another portrait visible when held up to bright light. The watermark is formed by varying paper density in a small area during the papermaking process, and does not copy on color copiers or scanners. A security thread appears in a different location on each new denomination. When held to a light you can see "USA TEN" or "USA TWENTY", etc., and flags in this thin thread. When viewed under ultraviolet light, the thread glows different colors. For $5 it is blue/purple, $10 is orange, $20 is a bright green, $50 is yellow, and $100 is pink-red. These colors arise from various fluorescent dye molecules used in the inks. Finally, for every new bill except the $5, a color-shifting ink feature is used. The number in the lower right corner changes from green to black as the bill is moved. The change in color is the result of multi-layered metallic flakes added to the ink. When the bill is tilted, light reflects off these flakes at different wavelengths and changes colors. This is called color diffraction, which is also responsible for the color variations found on the wings of some butterflies.

Follow the instructions very carefully. In fact, they say that an adult partner is needed if you are not 10 years old yet. We’ll give you a bit more of a scientific explanation here of what you’ll observe happening. You’ll first place the “magic rocks” into the bottom of a container and then pour a “magic solution” over them. The rocks are actually chunks of chemicals such as iron chloride (FeCl₃), cobalt chloride (CoCl₂), copper sulfate (CuSO₄), manganese sulfate (MnSO₄), and iron sulfate (Fe₃(SO₄)₂). Chemists call compounds like these transition metal salts. They are indeed salts but they are not edible so don’t even think about it! The colors of these particular salts are, respectively, yellow, purple, blue, pale pink, and green. There might be different salts, and therefore different colors, in your set. These are just examples. The solution is sodium silicate, also sometimes called “water glass”. What you are making is a structural precipitate and they are quite complex. The iron chloride salt, for example, changes by chemical reaction with the sodium silicate to a mixture of iron silicates and iron hydroxide. This mixture is gel-like. But the gels will change their texture to become more crystalline and brittle after a while.

An air bubble usually caps the slender shoots that form at first, so look carefully. They move jerkily, from one side to another. An elastic gel-like membrane is actually forming and breaking here.

If your set doesn’t seem to work very well it might mean that the sodium silicate solution has degraded a little bit, especially if the set is old. Most transition metal salts shouldn’t be affected by time, though.
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References:

• T. H. Hazlehurst, J. Chem. Ed. 1941, p. 286.
• B. Z. Shakhashiri, “Chemical Demos: A Handbook for Teachers of Chemistry”, 1983, Vol. 3, p. 379.

December, 2000

Remove 10 grapes from their stems, wash well to remove pesticides (which kill yeast), and tie them in a double layer of cheesecloth. Or use unwashed organic grapes. Using your hands, fold 4 cups of lukewarm water and 3-3/4 cups unbleached white bread flour in a large glass bowl until it¹s like lumpy papier-mâché. Swish the grape bag through the mixture and push it to the bottom. Either cover the bowl tightly with plastic wrap or transfer the mixture to a plastic container with a tight lid. Store at 70-75^oF. Remove the lid every day to record your observations. Fermentation has begun when you see bubbles and smell an odor. On day 4 you should see a yellow liquid. Any purple or brown spots are beneficial bacteria that also add unique flavor. Feed the yeast a cup of bread flour (which supplies sugar) and a cup of water. Mix well. On days 5-9 watch for any green, fuzzy mold. If it forms, remove it and add another cup of flour and water. On day 10, take out the grape bag and divide the mixture into two-cup "starter" portions. These can be given to friends and relatives, keeping one for yourself.

In a large glass bowl, add one cup of flour and one cup of water to your starter. Mix well. Cover loosely with a towel for about 8 hours. A lot of CO₂ gas will be given off here so do not use a tight-fitting lid. Repeat this step and ferment 12-14 hours. Add flour and water in this manner twice a day through day 14. During these feedings the dough should rise as enzymes from the yeast break down the sugars in flour and release CO₂ gas that is then trapped in the gooey gluten. In next month¹s column we¹ll bake the bread. If needed you can store your starter in a refrigerator, where it will become dormant.
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Reference: Nancy Lang, Scientific American Explorations magazine, Fall 2000, p. 14.