Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
January, 2003
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.
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.
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).
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.
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!