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, do you want to make a solid-liquid combination that can morph into weird shapes right before your eyes? All that you will need is some corn syrup, a thin, flat-bottomed dish (a Petri dish is perfect, but even plasticware will work), iron filings, and a strong bar magnet. Here is what you do with them. Pour a thin layer (very thin, less than 1/8") of the corn syrup into the dish. Add a small amount of iron filings to the syrup and stir. Put your strong magnet under the dish and move it around. What happens? Experiment with different ratios of iron filings to corn syrup by gradually adding more filings each time. Which ratio gives the best results? The best iron:syrup ratios will make a tiny but spectacular hedgehog of silvery spikes.
What's happening? The spikes form because the iron filings are drawn toward the magnet, dragging the syrup along with them. Individual spikes take shape as the iron filings pack together along the invisible lines of magnetic force coming from the magnet.
This is only a demonstration of a real high-tech magnetic fluid called a ferrofluid. What is the difference between the two? Size. Ferrofluids contain iron particles that are much smaller than these iron filings. In most ferrofluids the iron particles are really nanoparticles, at only 10 nanometers across. Look at a meterstick to see how small a millimeter (mm) is compared to a meter. One mm is a thousandth of a meter. A micrometer (mm) is a thousandth of a single mm, and a nanometer (nm) is a thousandth of that. In other words, one nm is a billionth of a meter! Chemists and materials scientists know well how to make particles this small.
Ferrofluids were first developed by NASA scientists in the 1960s as a way to control liquid fuel in low gravity. They added magnetic particles to the fuel and then manipulated it with magnets. In DVD players, magnets and ferrofluids work together as shock absorbers to control the vibrations that could make the player skip. The same technique is even used in audio speakers to improve sound quality by absorbing unwanted vibrations. Ferrofluids suspended between electronic parts by magnets create airtight liquid seals in computer hard drives and X-ray machines to keep out dust. And scientists are even looking at medical applications for ferrofluids, such as using magnets to perhaps guide tiny drops of the fluid mixed with cancer-fighting agents directly to a tumor.
There is no such thing as a liquid magnet, but solid magnetic particles that are really tiny can be suspended in a liquid that then behaves with magnetic properties. So, ferrofluids have the fluid properties of a liquid and the magnetic properties of a solid. When you are done with your experiment, dispose of the mixture in the trash (not in a sink). Iron filings can be purchased from a science supply store (including on-line versions). You can even "harvest" them from playground or beach sand using a strong magnet! (Warning though, this can be rather tedious to get a lot).
References: Check the "Fun Stuff!" link at www.strangematterexhibit.com and scroll down to the section on ferrofluids under "The Transformer". Strange Matter is a traveling exhibition developed by the Ontario Science Centre and presented by the Materials Research Society with the support of the National Science Foundation.
Kids, do you want to make some slimy, gooey worms for you and your friends? Of course you do! Here is what you will need. Have an adult partner buy some Gaviscon™ liquid antiacid and some calcium-fortified orange juice. Then all you need is some optional food coloring, a squeeze bottle with a narrow spout, a bowl (a shallow one works best), and a spoon. Fill the squeeze bottle with Gaviscon™ (here is where you can add food coloring if you like). Simply squeeze this into a bowl of the orange juice, and your worms should form instantly.
The longer the worms stay in the juice, the more rigid they become. You can lift them out using a pencil and touch them. Pull them apart to test how strong they are, for example, and if they get stronger the longer they sit in the juice (a few hours is best). What’s happening here? Your gooey worms are called polymers. A polymer is a large molecule made up of many smaller molecules linked together like a long chain. You can get an idea of this by hooking together a long series of paperclips. This chain represents the sodium alginate polymers in the Gaviscon solution. When these chains are put in the orange juice, the calcium ions (Ca2+) act to cross-link them. Make two paperclip alginate chains. Then, at a few points along the first paperclip chain, add dangling single clips and attach them to the other long chain. When you are done it should look a bit like a chain-link ladder. Imagine continuing this process to make a 3-D mesh, which happens the longer the worms sit in the juice.
The Gaviscon™ is needed because it has sodium alginate in the formulation. Sodium alginate is a commonly used thickener in ice cream, cheese spread, and even in the red pimento strips in green olives. Mixing this with the calcium ions that are in the orange juice forms the cross-linked polymer gel “worms”. You might also try calcium-fortified milk.
Reference: Check the “Stuff for Teachers” link at www.strangematterexhibit.com. This experiment is on page 25 of the Teacher’s Guide. Strange Matter is a traveling exhibition developed by the Ontario Science Centre and presented by the Materials Research Society with the support of the National Science Foundation.
Kids, is a tomato a vegetable or a fruit? Tomatoes are a fruit and,
in fact, they are more like berries than any other fruit. Like all berries,
wonderful when in season but mediocre when not. The problems with tomatoes
are that their season is very short and that they don't like to travel. The
same travel part can be said for bananas. And avocados, and more. Tomatoes
and many other fruits would never make the trip to the market when ripe. After
all, their job is to rot and deliver seeds.
Most commercial tomatoes are picked at the “breaker” stage when they have reached full size but have only a hint of red/tan/pink visible. So how is it that they're all an appealing red color by the time they all get to the market? After washing, sorting, sizing and packing, tomatoes are moved to an airtight room where they are exposed to a "ripening" agent. This agent is ethylene (C2H4) gas. Ethylene is a hydrocarbon that occurs naturally in many fruits and vegetables. As some fruits and vegetables mature, they produce their own ethylene, which continues the ripening process. Without ethylene, some items, such as bananas, would never ripen. Bananas are picked before they are mature enough to produce their own ethylene. After their journey from Central or South America up to here, they are placed in special rooms, which are then filled with ethylene to trigger the ripening process. The bananas are then sent to supermarkets, where they continue to ripen themselves by producing their own ethylene gas, going from the unripe green stages to the ready-to-eat yellow stage.
You can use a similar process to help ripen some fruit at home. For those that will ripen after harvest (only some, like avocados, can ripen after harvest; others, like pineapples, cannot), try this: Place a green tomato or hard avocado in a paper bag. Add a yellow banana or an apple and close. The banana or apple will give off their own ethylene gas and therefore help ripen the unripe fruit. Put similar unripe items into a bowl alone for comparison. These will also eventually ripen because fruits produce their own natural ethylene, but it will take longer. Wait several days, observing your fruit each day during the process. Occasionally we observe the detrimental effects of ethylene. For example, it can wilt flowers! Bananas and other ethylene-producers should therefore be kept away from fresh-cut flowers. Of course, you could intentionally try this in another experiment.
Ethylene producing fruits include apples, apricots, avocados, bananas, cantaloupe, figs, guava, honeydew, kiwi, mango, nectarines, papaya, passion fruit, peaches, pears, plantains, plums, and tomatoes. The experts say to keep supermarket tomatoes out of direct sunlight, and to never put them in the refrigerator. Below 50°F a volatile flavor compound called hexenal flips itself off like a chemical switch — permanently.
Kids, why do Mentos mints dropped into a can of soda make a foamy fountain?
One might guess that the acid in the soda might be reacting with some
kind of carbonate in the mint coating to create CO2 carbon dioxide
have a strange chalky color and texture and they do taste a bit like antacid
(calcium carbonate) tablets. However, the ingredients do not include
carbonates or, for that matter, any other significantly alkaline material.
contain sugar (sucrose), glucose, coconut oil, starch, emulsifiers, natural
flavor, and gum arabic. They are pretty much just big pellets of flavored
sugar with gummy stuff added to give them structural integrity.
Drop a Mentos directly into a freshly opened full can of soda. But wait! First, make sure that the can is in a sink or tray to collect the significant amount of foam that will spill over. In our labs, a mint Mento and a diet cola provided the most foam, causing about half of the soda to be lost. Using the can makes the foaming more spectacular than if you poured the soda into a glass because of the small opening.
So why do Mentos make soda foam up? It's a physical reaction, not a chemical one. Ordinarily, water resists the expansion of bubbles in the soda. Water molecules attract each other strongly, forming a tight mesh around each bubble. It takes energy to push water molecules away from each other to form a new bubble, or to expand a bubble that has already been formed. The property is called surface tension. The oils, emulsifiers, and gum arabic from the dissolving candy disrupt the water mesh, so it takes less work to expand bubbles. At the same time, the roughness of the candy surface provides many little nooks and crannies (more surface area) that allow new bubbles to form more quickly. As more of the surface dissolves, both processes accelerate, and foam rapidly begins to form.
You can see a similar effect when cooking potatoes or pasta in a pot of boiling
water. The water will sometimes boil over because organic materials that
leach out of the cooking potatoes or pasta disrupt the tight mesh of water
at the surface of the water, making it easier for bubbles and foam to form.
Root beer can also foam over if a scoop of ice cream is added, for essentially
the same reason. The surface tension of the root beer is lowered by gums
and proteins from the melting ice cream, and the CO2 outgassing from the root
blows the foam.
Test this hypothesis by dropping a Mentos into orange juice or any acidic but non-carbonated drink, or by dropping a Mentos into completely flat soda. What happens? Why? (Mentos is a registered trademark of Van Melle USA Inc.)
Experiment suggested by Steven S. Trail (BP Chemicals).
As an interesting sidelight, teacher Lee Marek of Naperville North High School, Naperville, IL, developed this into a demo for the Letterman show.
Fred Senese email@example.com,
Kids, have you ever heard the term “ppm” or parts per million? Sometimes a scientist will have to discuss what is in water or air at very low levels, and they use the term ppm because the amounts are so small. Even parts per billion (ppb) is used sometimes. One ppm means that one part of something exists in one million parts of the liquid, gas, or solid that it is found in. But just because these numbers sound so small does not mean that they are not important. For example, a fish (such as bass) needs at least 4 ppm dissolved oxygen in their water, and the air quality standard for sulfur dioxide (SO2, a pollutant) is 30 ppb. Chemists can detect to even parts per trillion levels for some materials using the right instrumentation.
This column will make use of more typical laboratory equipment than we usually require, but you can use ounces (oz) instead of milliliters (mL) and use common kitchen measuring tools as well. We will give measurements in both units. We are going to make a series of solutions of progressively higher dilution, and then test for the presence of a substance. This will demonstrate that something can be present at ppm levels even though we cannot see them with our eyes. You will need 8 small clear containers, milk, a small flashlight or laser pointer, a dark surface, and 100-mL and 10-mL graduated cylinders (or measuring cups to measure 1 and 10 ounces).
Measure and pour 100 mL (or 10 ounces) of milk into one of the containers, and do the same for pure water into another container. Mark these as #1 and #2, which is 1/1 or one part per one. Then measure 90 mL (or 9 oz) of water into each of the other six containers, marking them as #3-8. Pour 10 mL (or 1 oz) of milk from #1 (using the smaller graduated cylinder or measuring cup) into container #3. This concentration is 1/10, or one part per ten. Continue this serial dilution taking 10 mL (or 1 oz) from #3 and adding it to #4, and so on. They will progressively decrease in concentration as 1/100, 1/1000, 1/10,000, 1/100,000, and 1/1,000,000 (one ppm). What do you observe? Now place them on a dark tabletop and turn off the lights. Shine a flashlight through the side of the container and through the liquid. (Alternatively, have an adult partner use a laser pointer. But take care never to shine this in anyone’s eyes, including your own).
Look down on top of the liquid surface from above. What do you observe? It is hard to see any light pass through the pure milk because it is so thick. Next shine the light through the container of pure water, look down, and you shouldn’t see anything except the light on the other side. Containers 3-8 are another story, however. Shining the light through them at the side and looking over the top, you should see the beam of light right in the liquid as it passes through. Even though the last three containers (#6-8) look clear to the eye, there is enough milk present to scatter the light, albeit more weakly as the solutions get more dilute. The light is visible here due to what is called the Tyndall effect, a light scattering phenomenon. The light is scattering from colloids (proteins and other very small particles) in the milk.
Provided by K. A. Carrado and J. Sullivan, Argonne National Laboratory
Kids, we have cooked up a treat for you just in time for Thanksgiving. This activity will involve the baking of an unusual apple pie, one that needs no actual apples. It tastes and looks like apple pie because some tricks of chemistry are used to reproduce the taste of apples, and other ingredients are used to resemble the look and texture of apples. The classic recipe for this (“Mock Apple Pie”) can be found on the back of a box of Ritz™ crackers. There are also a few slightly different recipes available on the internet (see the links below for “Chemical Pies”).
The classic recipe is repeated here. You will need: two 9-inch pre-made pie crusts, 36 Ritz™ crackers (coarsely broken up), 1-3/4 cups water (H2O), 2 cups sugar (sucrose, C12H22O11), 2 teaspoons cream of tartar (potassium bitartrate or potassium hydrogen tartrate, KC4H5O6 or KO2CCH(OH)CH(OH)CO2H; these are all the same thing!), 2 tablespoons lemon juice and the grated peel of one lemon, 2 tablespoons margarine or butter, and 1/2 teaspoon ground cinnamon. Step 1. Line a 9-inch pie plate with one pastry shell. Place cracker crumbs in the shell and set aside. Step 2. Have an adult partner heat the water, sugar and cream of tartar to a boil in a saucepan and then simmer for 15 minutes. Add the lemon juice and peel, then let it cool. Step 3. When cooled, pour the syrup over the cracker crumbs. Dot with margarine or butter and sprinkle with cinnamon. Cover with the remaining pie shell. Slit top crust to allow steam to escape. Step 4. Bake at 425oF for 30 to 35 minutes. Cool completely and enjoy eating your experiment.
If you were to give a piece of this pie to an unknowing friend or relative telling them that it is apple pie, chances are that they will eat it, like it, and never know the difference. Why does this work so well? The cream of tartar produces a weak acid which, when combined with the other ingredients, produces the tangy taste of apples. The pieces of cracker closely resemble the texture and appearance of apple pie. Our senses of taste and smell are then tricked into thinking that it is, indeed, apple pie. Because our senses can be easily tricked this way, as scientists we must use sensitive instruments to accurately measure and identify substances and the changes that occur around us.
Kids, can you make popcorn kernels dance? This particular dance will be up and down rather than side to side. You will need two clear glasses or containers, water, clear soda water, and several uncooked popcorn kernels. Fill one glass with water and the other with soda water, then drop a few popcorn kernels in each. Notice whether they sink or float right away. Then wait a few minutes to see where they are and what they are doing. Tap the side of the containers and notice what happens.
The popcorn should sink to the bottom of the water glass and stay there pretty much forever. As for the soda glass, however, what do you think makes the kernels float after awhile, and what makes them sink again? This cycle is possible using the power of tiny bubbles. Bubbles of carbon dioxide, that is. When enough bubbles stick to the kernels, buoyancy lifts them to the surface. There, the bubbles burst and the kernels sink again. Tapping also makes the bubbles come loose. Your sink-float-sink cycle should last about 1/2-hour before the soda gets too flat. Do you know another way to make a solution with carbon dioxide bubbles? Start with water, add some vinegar, then sprinkle in some baking soda, and voila! The acetic acid (CH3COOH) reacts with the sodium bicarbonate (NaHCO3) to make carbon dioxide gas (CO2), water (H2O), and sodium acetate (NaC2H3O2).
Previous ChemShorts columns about this activity have appeared; see “Dancing Raisins” 2/92 and “Floaters and Sinkers” 1/93. The latter suggests items and amounts needed for an impressive large-scale demo.
“52 Amazing Science Experiments” by Lynn Gordon, 1998; Chronicle Books, San Francisco, CA