ChemShorts for Kids   --   1992
Copyright ©1992 by the Chicago Section of the American Chemical Society

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

ChemShorts Home

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

THE NAKED EGG


Kids, do you want to try to remove the shell from a raw egg, without breaking it?

First, place a raw egg in a 1-pint glass jar with a lid (mason jar, for example). Do NOT crack the egg! Then pour in enough clear, white vinegar (preferably from a newly opened bottle) to cover the egg. Close the lid and check it every once in a while over the next 24 hours. What happens? Bubbles start to form on the egg shell immediately, which increase in number as time goes on.

After 24 hours the shell will be gone (some pieces may be floating). But the egg remains intact because of a thin membrane, though which the yolk can be seen. Why? The chemical in vinegar is acetic acid (a weak acid). Egg shells are made of calcium carbonate, another chemical compound. When these two substances react, carbon dioxide bubbles form from the carbonate and the egg shell disappears.


DANCING RAISINS


Kids, would you like to make your own "dancing California raisins" by using chemistry? All you need are two clear plastic cups, one filled with water and the other filled with a cold, clear soda like 7-Up. And raisins of course.

First put a few raisins in the water. What happens? They sink. Why? The raisins are heavier and more dense than water. Now put a few raisins in the soda. This time they should also sink, but then gas bubbles of carbon dioxide will stick to the raisin and eventually lift it with them to the top. Then what? The bubbles pop and the raisins sink again, whereupon its "dance" can continue! Now, what does this tell you about how a life jacket works?


GREEN PENNIES


Kids, how would you like to turn your nice shiny copper-colored pennies into green ones? All you need is a saucer, a paper towel, vinegar, and 3-5 pennies. Fold the paper towel in half and then in half again to make a square. Put in on the saucer. Pour over enough vinegar to wet the towel, then place the pennies on top of the wet towel. Wait for 24 hours and.....what happens? The tops of the pennies should turn green. Why? Vinegar is a dilute solution of the chemical called acetic acid. The acetate part of this acid combines with the copper of the pennies to form the green coating, which is copper acetate.


OPERATION GLUE


Kids, what do Little Miss Muffet's curds & whey have in common with glue? Just what is a curd, anyway? Curds are a milk protein called casein (a natural organic polymer) which actually has a lot of industrial uses. One of them is a key ingredient in Elmer's Glue-All. In Operation Glue, YOU can produce glue from milk using ordinary household products.

Place 1/2 cup skim milk in a glass or jar. Add 1/8 cup vinegar and stir for a few minutes. Small lumps, which are curds, will form. Let them settle for a few minutes, then pour off as much liquid (the "whey") as possible. Filter the remainder through a cheesecloth until the curds are dry, and return them to the glass. Add about 1/2 teaspoon baking soda (for neutralization) to the curds, and mix. If the glue is too thick add a few drops of water. Now test your glue with a few pieces of paper.

Notes: The process of separating curds from whey is very similar to the making of cottage cheese. Do not save the glue. Wash up with water. Whole milk will not work because the fat molecules precipitate with the casein and interfere with the glue structure, making it too weak.


DYED-IN-THE-WOOL


Kids, did you know that most of the natural color of convenience foods is lost during processing? Food manufacturers add artificial coloring to foods to restore their expected color. Red food dyes are added to hotdogs that would otherwise look gray, for example. Natural food colorings (pigments from paprika, beets, carrots, and leaves) fade with time and generally have a low coloring power.

A long time ago chemists discovered how to make good dyes from coal tar, and the FDA has certified four - one blue, two reds, and one yellow - as safe to eat. This experiment will let you detect coal tar dyes in food. You'll need colored liquids like tomato or beet juice, soda, tea, maraschino cherries, grenadine, jellies, water from canned and cooked vegetables; powders like paprika, saffron, or turmeric in 1/2 cup water. Also, a small enamel or steel saucepan (aluminum pans won't work!), vinegar (acetic acid), and white wool yard (not acrylic).

Put some of a colored liquid, a few drops of vinegar and a 3-inch piece of the yarn into the pan and heat to boiling. Make sure that an adult is there to supervise this step. Lift out the yarn with a fork and rinse it in cold water. If the yarn is colored (dyed) after this boiling step, then the colored liquid contains an artificial dye made from coal tar.

The protein in wool reacts with coal tar dyes in an acid environment (vinegar) to form a new stable substance via chemical bonding. Natural dyes do not form this bond with the wool and easily wash away with hot water. Now check your results against the food labels.


COLA EXPERIMENTS


Experiment #1. Kids, imagine a cooler filled with cans of soda at a summer picnic. Did you ever notice that all the diet soda cans float on top of the ice-cold water, while the rest have to be fished out from the bottom? You can see this for yourself if you have a can each of a regular and diet soda. Put them in a large container of water like an aquarium, a cooler, or even the bathtub. Both cans are the same size but they weight different amounts because of the extra 2/3 ounce of sugar in the regular soda. It is enough to make the heavier one sink and the lighter one float on water. The cans differ in their "density", which is the amount of mass in a certain size. Mass is the amount of matter in a body (an astronaut weighs less on the moon but has the same mass as on earth).

Experiment #2. One of our sources tells us that Coca Cola contains only traces of extracts from the coca plant and the kola nut. In this experiment you can come pretty close to making one of the most closely guarded of all trade secrets - the formula for Coke. Mix well in a glass: 1 tablespoon + 1 teaspoon sugar, 1 teaspoon vanilla extract, 1/2 teaspoon bottled lime juice, 1/2 cup club soda, and a sprinkle of cinnamon. Close your eyes and give it a try, you might be surprised! This mixture will look very different from real colas because there are no artificial colors added yet. Experiment with the amounts of the ingredients a little bit to get the taste just right. Bon Appetit!


MAGIC WRITING


Kids, let's try to write a message that will appear as if by magic on paper, using chemistry. You will need a soup bowl, some tincture of iodine, a lemon, some notebook paper, a cup, and an art paintbrush.

Procedure: - pour 1/2 cup water into the bowl - add 10 drops of iodine to the water and stir - squeeze the juice of the lemon into the cup - cut out a smaller-than-bowl-sized section of paper - dip the art brush into the lemon juice and write a message on the paper - let the juice dry on the paper - put the paper in the iodine solution in the bowl

What happens? The paper should turn a blue-purple color everywhere except where the message was written, so that the words are outlined by a dark background. Why? When starch molecules in the paper combine with iodine, the combination is blue-purple in color. But Vitamin C (from the lemon) combines with iodine to form a colorless molecule. The area covered with lemon juice remains unchanged in color because of this.


MAGIC COLORS


Kids, here we will separate the colors in ink and make a rainbow effect. You will need green and black water-soluble marker pens, a cone-shaped coffee filter (for Melitta coffeemakers), a saucer, and water. Regular coffee filters are too wrinkled and thin to work well. About 1/2 inch above the rounded edge of the flat, cone-shaped filter, make a thick, dark green line about one inch long parallel to the edge. Do the same with the black marker about one inch away from the green mark. You can do the same on the other side of the cone if you like. Pull out the filter so that you have a shape like an upside-down ice cream cone.

Fill the saucer with water, but only enough so that the water line is below your pen lines. Place the rounded edge of the cone in the water and let it sit for about 10 minutes. If there was too much water (above the ink lines) it will just wash off the ink. Let the water rise on the paper until it reaches about an inch from the tip of the cone. Then take it off the saucer and let it air dry.

A trail of color (purple, orange, pink, and yellow for an Expresso marker pen) should be separated from the black ink, while the green ink should make a trail of blue and yellow. This happens because black and green are combinations of many other colors. As the water rises on the paper, the ink dissolves in it. The colors separate and rise to different heights because of differences in the chemicals producing the color. The lighter-weight chemicals will move the fastest, which means that they will move with the water to the top of the paper.


CARBON DIOXIDE TESTS
Part I. Limewater


Kids, here you will make a solution that can test for the presence of carbon dioxide (CO2 ) gas. This is a two-part project. Save the limewater you make for use in the next issue of ChemShorts. You will need two glass quart jars with lids, a tablespoon, and lime (CaO, the substance used in making pickles, not the small green citrus fruit). Fill one jar with water. Add one tablespoon of lime and stir. Secure the lid and allow the solution to stand overnight. Pour off the clear liquid into the second jar very carefully, do not let any of the settled lime sneak in. Keep the jar of clear limewater closed until needed.

At first the liquid should be milky white and opaque. Opaque means that light cannot pass through, making the solution impossible to see through. The milky appearance is due to undissolved particles of lime that are temporarily suspended in the water. It takes time for all of these particles to settle down. The resulting clear liquid contains as much dissolved lime as it can hold before settling out. This is called a saturated solution. It is similar to dissolving Kool-Aid or lemonade crystals in water. When too many crystals are used, the extra settles out on the bottom.

The jar must be kept tightly closed so that carbon dioxide from the air won't dissolve in it. We have other plans for this solution.

(Notes: Do not let anyone drink this solution and let an adult partner handle the lime for you).


CARBON DIOXIDE TESTS
Part II. Chemical Breath


Kids, now we can use the limewater made last month to test for carbon dioxide (CO2 ) gas in your exhaled breath. You will also need a straw and a pint-sized jar. Fill this jar halfway with the limewater. Use the straw to exhale your breath into the limewater, and continue until the clear solution turns milky. Why does this happen? Limewater always turns milky when CO2 is mixed with it. The chemical in the limewater is dissolved calcium oxide (CaO). This combines with the CO2 gas to form a white powder called calcium carbonate (CaCO3 ). This is not at all soluble in water, kind of like sand does not dissolve at all. Have you ever heard of limestone? This is what you just made with your own breath! The powdery limestone precipitate should settle to the bottom of the jar after several hours.

(Notes: do not drink this solution - take care with the straw to only exhale, not inhale).

Reference: Janice Van Cleave in "Chemistry for Every Kid", Wiley: NY, 1989.

Updated 2/12/99