Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Hard Water Test
Kids, in this experiment you will make "hard" water from distilled water, which contains no minerals, and is therefore "soft" to start with. Tap water in many parts of the country (including Chicagoland) is hard and contains minerals that can interfere with the cleaning ability of detergents. Water softeners remove these minerals. You will also compare the sudsing ability of a detergent in soft and hard water.
You will need: 2 cups (500 ml) distilled water, 1 teaspoon (5 ml) epsom salts, 2 empty and cleaned 2-liter plastic soft-drink bottles with screw caps, and several drops of liquid dishwashing detergent. Pour 1 cup (250 ml) of distilled water into each of the empty soft-drink bottles. Add the epsom salts to one of the bottles and swirl until they dissolve. Add several drops of liquid dish detergent to both bottles. Seal the bottles with caps and shake. A large amount of suds will form in the bottle without epsom salts. Far fewer suds will form in the bottle containing the epsom salts.
The suds formed in this experiment are made of tiny bubbles. The bubbles are formed when air is trapped in a film of liquid. The air is trapped when it is shaken into the water. The film of liquid surrounding each bubble is a mixture of water and detergent. The molecules of detergent form a sort of framework that holds the water molecules in place in the film. If there were no detergent, the bubbles would collapse almost as soon as they are formed. You can see what this would look like by repeating the experiment but leaving out the detergent. This experiment will not produce suds if detergent for a dishwashing machine is used. (Try it and see.) No suds are formed because automatic dishwasher detergent is formulated so that it does not form suds. Suds create major problems in a dishwasher.
The minerals that make water hard usually contain calcium and magnesium. In this experiment you made water hard by adding epsom salt, which is magnesium sulfate (MgSO4). Calcium and magnesium in water interfere with the cleaning action of soap and detergent. They do this by combining with soap and forming a scum that does not dissolve in water. Because they react with soap, they remove the soap and reduce its effectiveness. This could be overcome by adding more soap, but the scum will make what is being washed appear dingy.
Water can be softened in a number of ways. An automatic water softener connected to water supply pipes removes magnesium and calcium from water and replaces them with sodium. Sodium does not react with soap or detergents. If you don't have an automatic water softener, you can still soften laundry water by adding softeners directly to the wash water. These softeners combine with calcium and magnesium, preventing the minerals from forming a soap scum.
Reference: B. Shakhashiri at http://scifun.chem.wisc.edu/HOMEEXPTS/SOFTWATR.html
Kids, did you know that Silly Putty®, in addition to being the pinkish, bouncing, stretchy stuff, is also a "dilatant" chemical compound? Silly Putty is a unique material. It stretches without breaking, yet it can be "snapped off" cleanly. It bounces higher than a rubber ball. It floats if you shape it in a certain way, yet sinks in others. It can pick up pencil marks from pages and comics from some newspapers. If you slam it with a hammer, it keeps it shape, yet if you push with light, even pressure, it will flatten with ease. Gravity has a slow, yet devastating effect on Silly Putty creations.
All kinds of information can be found at: www.sillyputty.com/default.htm. There are even some experiments described there for you to try, such as "Floating Silly Putty", "Making It Bounce", "Silly Putty Running", "Squishing Silly Putty", and "Stretching and Snapping". We'll describe one here. When you shape Silly Putty into a ball it will bounce great on a hard, smooth surface. Cooling it actually improves its "bouncability." Shape it into a ball and bounce it. Measure how high it bounces. Then place the ball in the freezer for about an hour. While it's still cold, bounce it the same way you did when it was warm and compare the result. Silly Putty is said to have a rebound of 80 percent, meaning it will bounce back 80 percent of the height from which it was dropped.
As we said before, Silly Putty is a dilatant - a silicone based polymer that is highly elastic, exhibits high bounce, can be easily molded, yet can hold it shape while at rest. It was invented by a chemist at General Electric who was working on synthetic rubber substitutes, at first by mixing silicone oil with boric acid. Warning, here are some more big words: a dilatant is a "non-Newtonian fluid" for which "viscosity" increases as the "shear rate" increases. This is called shear-thickening. There are four different kinds of non-Newtonian Fluids based on viscosity behavior and a dilatant is one of them. Examples of regular Newtonian fluids include water, soda, and gasoline; some non-Newtonian fluids are wet clay, Gack (12/94 ChemShorts), and starch in water (see 4/93 ChemShorts "Tangled Molecules").
Silly Putty is also reported to be a "grip enhancer", used by athletes to increase hand strength. Unfortunately though it no longer lives up to what us older folks remember to be it's best quality. Changes in printing inks and processes, not in the putty itself, have limited its ability to pick up newspaper images. And just in case you or your parent needs to know, there is a method at www.crayola.com (see "Helpful Information") for removing Silly Putty from carpet.
Reference: Ann Thayer, Chemical & Engineering News, 11/27/00, page 27. Dilatant info is at: www.sasked.gov.sk.ca/forum/science/archive/messages/1958.html
A Chemical Counterfeit Test
Kids, what's so special about the paper that money is printed on? First of all, it isn't really paper at all. Rather, at a blend of cotton and linen, it is more like fabric material. The blend is about 3/4 cotton and 1/4 linen but the precise amounts are kept very secret.
As you can imagine, the U. S. Bureau of Engraving and Printing uses many different methods to try to stop counterfeiters. We've written about some of them in this column before (see 3/93 for magnetic inks and 10/00 on the "Science of Money"). Here we'll describe one chemical test that you can do to spot the fake in a stack of bills.
Real paper is either coated or "sized" with starch. Starch sizing means that starch has been added to ordinary paper to fill the gaps between cellulose wood fibers. It acts to stiffen the paper very much like the way laundry starch stiffens a shirt collar. It also makes paper less absorbent to ink. Without sizing, ink would smear out all over the paper fibers and make words blurry. Paper money, however, has to completely absorb and bind ink. Did you ever wash a bill accidentally in the laundry? It comes out good as new without any loss of ink whatsoever. No starch sizing is used in the production of currency paper.
So, a test for starch is a great way to tell the different between real and fake money. Here's how to do it yourself. To see how a dilute iodine solution (you can find this at a drugstore) reacts with starch, dab a little bit using a cotton swab onto a slice of raw potato. The deep blue-black color that results is a positive test for starch (potatoes are full of starch). It happens when the yellow-red color of iodine combines with starch molecules. Now dab some iodine onto regular paper and see if the same thing happens (it should). Now repeat the test with a dollar bill. Did you get a positive starch test? You shouldn't!
Reference: E. Venere, "The Money Makers" in ChemMatters, 2/03, p. 14 and in Chemistry (both American Chemical Society publications, the latter a quarterly newspaper).
Kids, did you ever wonder why everyone calls that stuff in pencils "lead" when it isn't really lead at all? Instead, it is a nontoxic mixture of graphite and clay (more on that later). Way back in the days of the Roman Empire, actual lead rods were used to write on papyrus. But more recently, in the 1500's, a graphite mine was discovered and graphite was found to leave darker marks on paper. At the time, everyone thought that graphite was a type of lead. They called it black lead or plumbago. The chemical symbol for lead is Pb, which stands for the Latin word plumbum (check www.vanderkrogt.net/elements/elem/pb.html for a complete history of lead).
By nearly 1800, chemists finally proved that black lead was really a form of carbon. Carbon exists in the elemental form as either graphite or diamond (or, as we have recently discovered, nanotubes and buckyballs). Because graphite is so soft, it needs a holder to support the skinny sticks used for writing. Low quality graphites need to be further strengthened by mixing with clay and water (see the Nov. 1996 ChemShorts to learn more about clays). A slurry of these three ingredients is crushed, mixed for three days, extruded into the thin rods, and then heated to dry out the water. The ratio of clay to graphite affects the hardness of the "lead": the more clay, the harder the pencil lead. This means that less graphite is present to transfer to the paper, resulting in lighter lines. The higher the number, from 1 to 4, the harder the lead. Get a sampling of pencils of various hardnesses and check out their writing ability on different types of paper.
Various woods have been used for the pencil casings, from red cedar to the now most commonly used incense cedar. This beautiful wood is then coated with five to eight coats of paint. The traditional yellow paint also has a history. When a very pure graphite mine was discovered in China in the 1800's, pencils made with this high quality Asian graphite (no clay necessary) were painted yellow to distinguish them from the rest. Erasers are added and various markings are then stamped onto the pencil shafts. Did you ever notice the word Ticonderoga stamped on many of them? Fort Ticonderoga, a Revolutionary War fort in upstate New York, is near one of the purest graphite deposits ever known at 99.9% pure carbon.
We don't advocate that you try this, but a pencil will on average write about 45,000 words, or a line 35 miles long! It is claimed that such a line will in fact even conduct electricity because graphite is a known conductor. Colored pencils are made from chalk, clay, or wax mixed with binders and pigments; compare writing with some of these alongside your regular pencils. If it is possible for you to get a sample of a chunk of graphite (maybe at a store that sells gems, minerals, and fossils), take a close look at it and compare it to the stuff in your pencil.
Reference: Steve Ritter, Chemical & Engineering News, ACS, 10/15/01, pg. 35 (http://pubs.acs.org/cen/whatstuff/stuff/7942sci4.html).
Kids, did you ever wonder why newspaper ink comes off all over your fingers? Okay, maybe you haven't read too many newspapers yet, but now is a good time to start. Open up a newspaper, read the headlines, flip every page, and re-fold every section. By now you should be good and covered with black ink. Why doesn't that happen when you read a book or a magazine? Or this newsletter? Since we learned all about pencils in last month's column, now is a good time to learn something about inks.
On the face of it, ink is simple; it is a pigment or dye that is dissolved or suspended in a liquid (solvent). This is pretty much the same thing as paint. There are two classes of inks, called printing and writing inks. The two main printing inks are for regular printing (using mechanical plates) or for digital printing (like in ink-jet printers). Writing inks are what you would expect - the type found in pens.
First let's talk a little more about printing inks. Black printing ink is carbon black in a solvent. Color printing inks use organic (C,H,N,O-based) pigments, usually nitrogen-containing salts of dyes with fancy names like "yellow lake", "peacock blue", "phthalocyanine green" and "diarylide orange". A few inorganic (non-carbon) pigments are sometimes used, like chrome green (Cr2O3), Prussian blue (Fe4[Fe(CN)6]3), and cadmium yellow (CdS). The solvent for these dyes is usually linseed oil, soybean oil, or a heavy petroleum distillate. White pigments such as titanium dioxide (TiO2) can be used to adjust the colors also.
In terms of writing inks, the older fountain pens used water-based solvents. In the 1950's, ballpoint pens were developed that use pastelike, oil-based dyes. The thickness allows capillary action to keep the ink flowing evenly, are non-smearing, and quick-drying. Water-based solvents are still used in markers, highlighters, and rollerball pens, though.
So, back to our original question. Newspapers are usually printed with mineral oil ink at a very fast rate (like 3,000 feet/minute!). When other media are printed, like books or magazines, linseed oil inks are allowed to dry in the air. Or, paper printed with inks made from alcohol- or petroleum-based solvents are heated and evaporated to dryness. Because newsprint can't be allowed the time for heating and drying, the ink is absorbed by the inner fibers of the paper, and always sit there a bit damp, never evaporating completely. Also, the type of paper used is different (see 11/96 "ChemShorts").
Are you curious about how much ink it might take to print a page like this one? A regular ballpoint pen seems to last a really long time before the ink runs out (usually we have lost the pen long before that happens). A magazine of, say, 80 pages needs 68 gallons of ink for 150,000 copies. This works out to about 20 microliters (which is 1/1000th of a milliliter) per page - a real bargain. After washing the newsprint off your hands, gather up a few different kinds of pens, highlighters, and markers, and create a piece of artwork while thinking about the chemistry coming out at your fingertips!
Reference: Steve Ritter, Chemical & Engineering News, ACS, 11/16/98, 76(46), in the "What's That Stuff?" column. (http://pubs.acs.org/cen/whatstuff/stuff/7646scit2.html).
Helium vs. Air Balloons
Kids, did you ever notice that helium balloons made using a regular balloon (not a Mylar balloon), do not last very long? This column provides a way to measure the diffusion of helium out of a balloon, and compare the results to a balloon filled with air.
You'll need a package of regular balloons, a helium gas source, a yardstick, and a tank of water large enough to hold a submerged balloon (a bathtub might work). Blow up three balloons with air and three balloons with helium, all to approximately the same size. Measure their volume by submerging each one into the tank of water, and measuring the "displacement". This means that you'll measure the height of the water before the balloon is added, again after it is submerged, and subtract to get the result.
Then measure the heights again after predetermined amounts of time, such as every few hours, until you see no change in the measurements (the balloon has deflated). Plot your results of water height vs. time. The idea is to see which balloon diffuses the gas it is holding more quickly. The answer is that, since the helium molecules are smaller than air molecules, helium should diffuse out faster. You could also test different brands of balloons to do a comparison.
What do the results tell you about regular balloons and Mylar balloons? Both are made of polymers, but the spaces between the individual chains of molecules (polymer chains) are quite different. Mylar is an exceptionally strong polyester, while many regular balloons are made of latex.
Reference: This activity came to us courtesy of Ms. Adrian Winans, who performed this as a fourth-grade science fair project.
Thermite - A Solid Reaction
Kids, can you imagine doing chemistry with just aluminum foil and some rust? By using these compounds in just the right way, you can perform a simple yet rather spectacular process that is one example of the so-called "thermite" reactions. A full-scale thermite reaction is much too dangerous for classroom demonstration, but you can get the idea by doing a scaled-down version with an adult partner.
First, find two large, rusted iron spheres such as old track-and-field shotputs or 2-3" diameter ball bearings - the rustier the better. Cover one with regular aluminum foil. While you are both wearing goggles and taking much care not to smash fingers, have your adult partner strike the spheres together with a glancing blow. Simply banging them together head-on will not work; they must be scraped and slid across each other like striking a match. When they hit just right, you will see and hear a mini-thermite reaction at the point of contact. The resulting sparks and noise are like firing a toy cap gun.
What's going on here? This thermite reaction is a single replacement reaction between iron(III) oxide (rust) and aluminum metal to make aluminum oxide and iron metal. Chemists write it as: Fe2O3 + 2 Al(0) " Al2O3 + 2 Fe(0) + heat. Because heat is released it is one example of an exothermic reaction. The heat release is so high in fact that temperatures reach 2,200°C! This is actually hot enough to melt iron, which has a melting point of 1,530°C. This property is put to good use for producing molten iron that welds train track rails together out in the field (see references below for more information on this).
One very interesting aspect of the thermite reaction is that it takes place in the solid state. Just a few reactions in nature occur between solids, and these few tend to go so slowly that they are rarely even noticed. Fires derived from thermite energy are quite difficult to extinguish. Unlike combustion, thermite fires do not need oxygen from the air to start, so the typical extinguishers using CO2 or other gases to smother flames are not very effective. And using water can be downright dangerous. The high temperatures decompose water into hydrogen and oxygen, causing even more explosions. So the recommended method is to cover the reaction with sand.
References: Michael Tinnesand, "Mighty Thermite", in ChemMatters, ACS, Feb 2002, pp. 14; A. L. Feliu, "Thermite Welding Gets High School Chemistry Class on Track", J. Chem. Ed., Jan 2001, pp 15.
JELL-O: Chemistry in a Box
Kids, the ingredients list on a box of JELL-O® tells us that it is sweetened, flavored, and colored gelatin (take a look yourself). A box of strawberry JELL-O has sugar, gelatin, adipic acid (for tartness), artificial flavor, disodium phosphate and sodium citrate (to control acidity), fumaric acid (for tartness), and the dye red 40. Most of us like JELL-O, of course. But we bet that you will be quite surprised to learn that gelatin is essentially processed collagen, which is a structural protein in the connective tissue, skin, and bones of animals. Collagen also makes up about one-third of all the protein in the human body. Collagen is composed of the molecules glycine, proline, hydroxyproline, and other amino acids. JELL-O itself has little nutritional value apart from energy (80 calories per serving). Gelatin by itself is an incomplete nutritional protein because it lacks tryptophan, an essential amino acid.
Structurally, collagen is three polypeptide chains wound together into a helix, like three strands of spaghetti twisted together. When collagen is heated in water, the triple helix unwinds and the chains separate, becoming random coils that dissolve in water: this is gelatin. As the gelatin cools, the molecules try to regain the original helical structure and eventually bond together as they lose energy.
The way that gelatin molecules bond can trap large amounts of liquid, resulting in a semi-solid "colloid". All colloids have a disperse phase and a continuous phase; that is, one substance is dispersed throughout another substance. In JELL-O, the dispersed phase is the solid gelatin and the continuous phase is water. Gelatin can absorb a tremendous amount of water at up to 10 times its weight. Go ahead and make a box of JELL-O, following the package directions with an adult partner, and think about the chemistry going on with the molecules there.
Here is some trivia about JELL-O to amuse your family and friends:
- Gelatin is also in treats such as marshmallows and gummy candies. In the pharmaceutical industry, gelatin is used to make the outer shells for hard and soft capsules. A brand-new application is in the paint ball industry, which uses gelatin to make paint balls.
- As immigrants passed through Ellis Island, they were often served a bowl of JELL-O as a "Welcome to America" treat.
- When hooked up to an electroencephalograph machine (EEG), an instrument that records the electrical activity of the brain, JELL-O demonstrates movement that is virtually identical to the brain waves of a healthy adult.
- Fresh or frozen pineapple contains an enzyme that prevents JELL-O from setting; canned pineapple can be used because the canning process eliminates the enzyme.
References: C. Marasco, Chemical & Engineering News, 5-19-03, "What's That Stuff?"; http://web.kraftfoods.com/jello/main.aspx?s=&m=content_main (check out the "JELL-O 1-2-3" fun kids page here as well); "JELL-O: A Biography" by Carolyn Wyman (Harcourt, 2001); www.gelatin-gmia.com.
Kids, did you know that October 19-25 this year was National Chemistry Week? The theme this year was "The Earth's Atmosphere and Beyond". All kinds of fun activities were developed for that week to highlight the chemistry going on in the air that we breathe. Here we are going to highlight one of them, which was made to help discuss wind.
Wind can carry smoke, dust, and gases hundreds of miles in just a few days. Satellite images of dust storms in the African Sahara Desert show that some of the dust actually travels all the way across the Atlantic Ocean and falls onto the southeastern U.S. Because we can't see air, we can't tell where it is going without clues such as seeing a cloud drift by or feeling it on our skin. This activity uses colored candy dropped into warm water to imitate the way that smoke, dust, and gases move in air.
Ask an adult partner to help you pour warm (not hot) water into a square plastic dish, one that is about sandwich-size. Pour the water about 1 inch deep. Placing the dish on a white tabletop or white piece of paper will help you see the effects best. Then get somes candies with hard shells in a variety of colors. Select three pieces each of four different colors. Put them into the water so that each corner of the dish has a different color. Keep the water as still as possible (no stirring!). Now watch carefully as the candies dissolve. Draw a picture of what you observe. You can try different types of candy for fun, but use the same kind of candy for each individual experiment. (This way, if you want to test more advanced concepts, you can compare factors such as dissolving rates and the way that different dye colors mix).
One of the early ways that scientists tracked how fast winds were blowing was by watching clouds. In this activity, you made clouds of color in the water. The clouds moved even though you did not mix the water. While we know that, in water, diffusion causes the apparent movement, we use this as an analogy for seeing clouds move in the sky. Just for fun, when you are done, go ahead and stir up the center using a spiral motion. Watch your candy clouds really move now, almost like the hurricane eyes we see on weather news doppler radar.
Here is an interesting sidebar to this experiment. One of the candies we tried this with were Starburst® Jellybeans. After the color clouds formed, we noticed that the tiny little Starburst® decals from each individual jellybean were floating on top of the water. They were fragile and dissolved after a couple of minutes. We speculate that these are made of a soluble, food-grade plastic such as gelatin or a cellulose derivative. A call to the Mars, Inc. Consumer Affairs Office yielded the following response: "The edible ink changes the crystalline structure of the candy shell and it takes longer to dissolve".
Reference: This and many other NCW activities can be downloaded from the www.chemistry.org website. On the left, where it says "Quick Find", click "Natl Chem Week". From there go to NCW Resources for Students and Educators and download the first publication. It's called "Celebrating Chemistry" and it has many hands-on activities and articles for 4th-6th grade students. Email firstname.lastname@example.org with any info about the Starburst® phenomenon.
Kids, did you ever wonder what the difference is between all those long, rectangular boxes of foils and wraps in your kitchen? This month we are going to have fun by making something tasty and then testing how best to keep it that way.
First, bake a batch of cookies with an adult partner. Make your favorite kind, especially considering that the holidays are just around the corner. Bake a third of them on a plain, ungreased cookie sheet, a third on a greased sheet, and the last third on a sheet that is lined with kitchen parchment paper. What do you notice when removing your cookies? Greasing a sheet or pan will make the surface slippery so that food won't stick (like one third of your batches probably did). Parchment acts the same way but has the added benefit of making cleanup easier. Why didn't the cookies stick to this paper? Why didn't the paper burn? This parchment paper is coated with silicone molecules, which makes it more slippery and heat-resistant than regular paper. Silicone molecules are polymers of -Si-O- groups (actually, -Si(R2)O- groups).
Now place half of the cookies on wax paper to cool, and the other half on paper (from brown paper bags or paper plates). When they are cool, what do you notice? Has the wax melted a bit? Wax paper is a thin sheet of paper that is coated with paraffin wax. Paraffin wax is a white wax made up of straight-chain hydrocarbons that contain 26-30 carbon atoms per molecule. And how about the paper that was used to cool the cookies? Are there greasy spots? Such spots are from the melted fat molecules (oil, butter) in the cookie recipe.
Last, store your cookies individually in different types of wraps and containers. Seal them in plastic wrap, ziploc bags, aluminum foil, wax paper, Tupperware, and paper lunch bags, for example. Every day for a few days in a row (or for as long as they last), test your cookies for freshness. Which method or methods work best? Why? Some materials make better barriers than others against water molecules (which can make things soggy) and air molecules (especially oxygen, O2), which can make cookies stale. Think about how tight the bonding has to be between aluminum atoms, for example, to not let the tiny oxygen and water molecules pass through. Chemists use scientific words like "permeation", "diffusion", and "percolation" when quantifying such properties.