ChemShorts for Kids   --   1993
Copyright ©1993 by the Chicago Section of the American Chemical Society

by Dr. Kathleen A. Carrado, Argonne National Labs

ChemShorts Home

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

Floaters and Sinkers

Kids, did you ever want to make a liquid in which you could watch objects automatically swirl around? Here you will make a liquid that generates enough carbon dioxide gas to make objects float and sink. In order to make a really nice display, you will need a one-gallon glass bottle, a full 16 oz box of baking soda, water, vinegar, spaghetti, raisins, and paper clips. This is a good scale to use for a demonstration in front of a class.

Pour the baking soda into the glass jar and fill about 3/4 full. Swirl to dissolve most of the baking soda and allow the rest to settle at the bottom. Add small amounts of vinegar to start the production of carbon dioxide gas bubbles. Then add several paper clips, raisins, and two-inch pieces of spaghetti and watch.

Carbon dioxide gas collects on the surface of the objects and causes them to float to the surface. At the surface, the gas bubbles burst, the object sinks to the bottom, and the process starts again. The gas forms from the reaction of sodium bicarbonate (baking soda) with acetic acid (vinegar).

Staying Dry

Kids, did you ever wonder how the new disposable diapers that are so thin can really work for your baby brothers or sisters? There are tiny beads in the filling that are able to absorb more than 300 times their own weight of water. Our purpose is to collect these beads and watch how they behave when exposed to water. All you need is an "ultra-absorbent" disposable diaper (Huggies Ultrathin, Ultra-Pampers), water, and table salt.

Cut open the diaper and carefully peel away the cotton-like filling. You will notice that it feels gritty. Separate the small gritty beads from the cotton fibers (tweezers and a small kitchen strainer may help, but are not really necessary). You should be able to easily get about 1/2 tsp. of beads, then pour them into a clear glass. Add about 1/2 cup of water and gently swirl, or pour the mixture back and forth between two glasses until it is too thick. (If you are able to get distilled, deionized water, it works better than hard tap water.) To "unlock" your gel, sprinkle a little salt on top and stir it into the gel. When the water is released the now syrupy liquid can be washed down the drain.

The superabsorbent beads are a co-polymer of poly(acrylamide) and sodium polyacrylate that can undergo physical changes quickly and reversibly with water. Other uses for these polymers are for hydro-mulching plants (places like Frank's Nursery now sell small bags of colored gel for this) and removal of water from jet fuels. Try your experiment again if you like with a drop of food coloring in the water (yellow fits the diaper theme nicely).
Reference: B. Z. Shakhashiri "Chemical Demonstrations", Vol. 3, chapter 9, p. 368.
Submitted by Kathleen A. Carrado, Ph.D. (with help from J. Ellefsen-Kuehn).
Argonne National Lab / (708)252-7968

Money, Munchies, and Magnetism

Kids, you probably already know that iron is magnetic. In this column, we will demonstrate a way to prove that there is iron metal in two places that you have probably not ever realized: a one dollar bill and a bowl of cereal! You will need a bar magnet (chemists can use long thin stir bars), a dollar bill (or $5, $10, $20 - they all work), and a box of cereal that claims to be high in "reduced" iron (like Total®).

First we will do the money experiment. Hold your bill straight down by the very edge of a short end - a newer bill works best because it will hang straight. With the other hand, slowly move the bar magnet lengthwise along the back of the dollar bill as close as possible without actually touching it. What happens? There should be at least one portion of the bill where it actually moves toward the magnet, or is "attracted". Why is this? Some, but not all, of the ink used in printing paper money is deliberately magnetic. This method is used to try to foil possible counterfeiters, and it also helps aid in the detection of counterfeit money!

In the second experiment, soak a few cups of the cereal in a large bowl of water until it is mushy. Vigorously stir the mixture with a wooden spoon for five minutes. Then add your bar magnet and continue stirring, more slowly, for several minutes. Carefully nudge the magnet around the bottom of the bowl a few times, then let the mixture stand for about ten minutes. Slowly pour off the "mush" and examine your bar magnet. Is it covered with small black needles and specks? This is the "reduced" iron (iron metal) that is actually added to the cereal because it is healthy for us to have iron in our diets. Chemists will find this easy to do using a magnetic stir plate, and a large beaker and stir bar. The more cereal you start with and the more time you give, the more iron you will collect!
Reference: From a "Weird Science" demonstration given by Lee Marek and Bob Lewis at Nalco on 12/4/90.
Submitted by Kathleen A. Carrado, Ph.D.
Argonne National Lab / (708)252-7968

Tangled Molecules

Kids, did you ever watch someone make spaghetti? If there are just a few cooked strands in a boiling pot of water, chances are they won't touch each other. But when a whole box is cooking the strands can't avoid touching each other. Some molecules are so long and skinny that they act like strands of spaghetti. In this experiment we will see how the long, skinny molecules called polymers can sometimes behave the same way.

To one-half cup of cold water add anywhere from 5 to 10 heaping tablespoons of household corn starch, one at a time with complete mixing each time. The amount varies with the quality of both the water and the cornstarch. You will know you have the right amount when the following tests work. Do you notice a difference between stirring very slowly and stirring faster, or between slowly lifting the spoon out and quickly pulling it out? How about putting your finger in slowly and touching the bottom of the bowl vs. jamming it in?

The starch mix should act almost like a solid when confronted with a fast motion. This is because the long, skinny starch molecules are very crowded and get tangled up with each other. When a slower motion is used, the molecules have enough time to move out of the way of each other (just like spaghetti!). Disposal: The mix gets thicker on standing, so immediately after finishing pour it into a large bowl of water and wash down the drain with lots of water.
Submitted by Kathleen A. Carrado and Henry L. Crespi
Argonne National Lab / (708)252-7968

Crystal Cubes and Needles

Kids, did you ever want to grow your own crystals? This experiment will show you how to make crytals with different shapes. You will need 2 saucers, 2 sheets of dark construction paper, 2 baby food jars with lids, epsom salt, and ordinary table salt. Fill the jars half-full with water. Add 2 tablespoons of epsom salts to one jar, and 1-1/2 tablespoons table salt to the other jar. Secure the lids, shake vigorously 60 times each, and then let them settle for several minutes. Cut circles from the paper to fit inside the saucers. Separately, pour thin layers of the salt solutions over the separate pieces of paper; try not to pour out any of the undissolved salts. Place them in a warm place and wait several days, observing daily.

On the paper wet with the table salt (sodium chloride) solution, you should see small, white, cubic crystals that increase in size each day. Sodium chloride salt crystals have a cubic shape. You should see long, slender, needle-shaped crystals on the paper wet with the epsom salt solution. "Epsom salts" is the common name for this chemical, but it is also called magnesium sulfate. When epsom salts are packaged, the needles of magnesium sulfate are first crushed. By dissolving in water and then allowing for slow evaporation, the needles and cubes are given the chance to build in size.
Submitted by Kathleen A. Carrado
Reference: "Chemistry for Every Kid" by Janice VanCleave, Wiley: NY, 1989.
Argonne National Lab / (708)252-7968

Really Food Coloring

Kids, did you know that you can draw pictures with fruits and vegetables, and that their colors can be changed using chemistry? To do this activity you will need an assortment of foods such as a radish, red cabbage, a carrot, grape juice, and spinach leaves. You will also need a sheet of white construction paper, vinegar, a 50/50 solution of baking soda in water, and cotton swabs. Rub the skins of the foods onto the paper, making three circles of color for each food, and label them. Use a swab for the grape juice. Again using a swab, rub the vinegar onto one circle of each food and the baking soda solution onto the second circle. Leave the third circle alone as a control. What do you observe?

Among other things, there are chemical compounds called "anthocyanins" in some plants. These compounds have different colors depending upon the strength of an acidic or basic solution. The vinegar (acetic acid) is a weak acid and the baking soda (sodium bicarbonate) solution is a weak base. Because of their ability to change colors, anthocyanins are one kind of indicator for determining the strength of an acid or base. Your results should have showed you that radishes, red cabbage, and grape juice all contain anthocyanins. They are also present in the petals of red roses. The major pigment in many green plants is chlorophyll, while that in carrots is called carotene; these compounds do not act as indicators. Try other fruits, vegetables, or plants with your new chemical testing system!
Submitted by Kathleen A. Carrado, Argonne National Lab
Reference: Ann Benbow of ACS, Coordinator of Pre-High School Science Office, who presented this at the CHEERS/PACTS Workshop on 4/17/93 at W. Aurora H.S.

Totally Tubular Plants

Kids, as you know, plants need water to live. Water goes from the root, up the stem, and into the leaves. Did you ever wonder how the stem is specially made so that water can travel up it? This experiment will help you find out. You will need a glass one-third full of water, blue food coloring, and a 8-10" stalk of celery that has been freshly cut on both ends by an adult partner. Notice the small dots on the narrow end of the celery stalk. Add 5 drops of the food coloring to the water and place the wide end of the celery in the water. After a few hours you should see that the little dots on the top of the celery are now blue. Use a fingernail to start pulling away one of the blue tubes at the top. Can you pull it all the way down and remove it totally from the stalk? Try another experiment with two new celery stalks. Carefully remove all of the tubes from only one new stalk and then place them both in the blue water. Compare them after 24 hours.

This activity should help you discover how water can move up through a plant stem. Many plants have a series of tube-like cells that bring water up, and another set that takes nutrients produced in the leaves down the plant. After 24 hours, the celery without the tubes should be much more limp than the piece with the tubes intact. You might also be surprised to see what happens to a white carnation after being placed in a glass of water with food coloring for several hours; try other food colors and make a multi-colored bouquet! (Hint: cut about 1" off the bottoms of the of the carnation stems first).
Submitted by Kathleen A. Carrado, Argonne National Lab
Reference: WonderScience, 7(5), May 1993.

Aluminum Trivia

Kids, let's explain why chewing an aluminum foil spitball can really hurt some people, while for others it is just a weird piece of gum. The difference is because some of us have silver fillings in our teeth. It turns out that aluminum atoms lose their electrons very easily. In the presence of our mildly acidic saliva, which acts as a catalyst, we have what amounts to a crude electric battery. Electrons flow from the aluminum to the silver amalgam filling. The current is felt by the nerves of our teeth and causes a downright unpleasant zing!

Aluminum foil will begin to decompose in the presence of many other acidic substances in a process called oxidation. Acids like to oxidize obliging metals. Some common acidic foods include ketchup which has a pH of 3.8 (7 is neutral), or a cola soda which is even more acidic with a pH of 2.7. Tell any cooks you know to never wrap a meatloaf glazed with ketchup or tomato sauce in aluminum foil for storage. After several hours the result of this contact is a grayish-black disgusting mush of aluminum oxide.

Brainteaser: why doesn't a full aluminum cola can dissolve? Chemistry solves that problem, too. The inside of the can is coated with a harmless but effective protective surface made up of long molecules called polymers (in short, a plastic coating).
Submitted by Kathleen A. Carrado, Argonne National Lab
Reference: (from p. 121 of The Straight Dope by Cecil Adams, 1984).

Giant Bubbles

Kids, you can make gigantic soap bubbles with a mixture of liquid soap or detergent, glycerin, and water. The glycerin is the secret ingredient that adds strength to the bubble solution. Mix together 1 part soap with 1 part glycerin and 6 parts water (distilled water works best). Pour into a large tray or cookie sheet.

Form a 12-inch circle with a handle out of stiff wire about the diameter of coat-hanger wire. You can try an actual coat hanger, but they are often coated to prevent rusting; this coating prevents the bubble solution from clinging to the wire. Dip the wire circle into the bubble solution and bring it out at an angle so that a film of solution fills the inside of the circle. Now sweep the wire through the air to form a large bubble. A twist at the end of the sweep helps to loosen the bubble from the wire.

A bubble is really three bubbles in one. There's an outside layer of water, a middle layer of soap and glycerin, and an inner layer of water. When bubbles these big break, they leave a lot of soap behind. Be prepared to wipe it up (cleaning the floor at the same time!), or make your bubbles outside.
Submitted by Kathleen A. Carrado, Chair
Elementary Education Committee
Reference: "Mr. Wizard's Supermarket Science", Don Herbert, 1980, p. 48.

An Incredible Edible Landfill

Kids, how much do you know about how your local landfill actually works? Let's build one of our own while we learn. A Keebler© ready-made chocolate pie crust will be our hole in the ground. Before any trash can go in, a landfill hole is lined with pipes to remove liquids from garbage and decomposition. Place Twizzler© licorice whips along the bottom of the crust for this purpose. Most real sanitary landfills surround the hole with an impermeable clay lining to prevent harmful waste from leaving the area; the foil tin containing the pie crust can represent this lining. Mix some "garbage" made of nuts, raisins, M&Ms, etc., into vanilla pudding to make your trash, and cover the bottom of the crust. In sanitary landfills, garbage is covered with dirt each day. Cover your vanilla pudding garbage with a chocolate pudding dirt layer. Make as many alternating pudding layers as you can until the crust is full. Make sure that the top is a chocolate pudding dirt layer.

The garbage we bury never really goes away completely. Not much decomposition occurs because air and moisture - needed by garbage-chewing microorganisms - are sealed out. Many landfills become parks, ski hills, and golf courses. Color some shredded coconut with green food coloring and sprinkle it over the dirt to look like grass. Your landfill is now complete and ready to eat! Dig in!

Submitted by Kathleen A. Carrado, Chair
Elementary Education Committee
Reference: "Solid Waste Activity Packet for Teachers", Ill. Dept. of Energy and Natural Resources, page 70. (Contact person: Kathy Engelson, Supervisor for School Education, IDENR, 217-524-5454. Also Jean Dehorn or Carol Fialkowski, Chicago Academy of Sciences, 312-549-0606 x2014).

Updated 2/12/99