The oscillating clock reaction (after mixing the color changes colorless to yellow to purple will reoccur many times over a several minute time period) naturally follows the clock reaction and is used mainly for its fascinating properties but it is also used as the basis of a brief discussion on the infancy of scientific discovery and how much there is still left to be investigated. Many children think scientists know everything. The point apparently gets across as students have written: "I know you guys don't know everything" and "I hope you find out about the ones you don't know." The word magic can also be discussed here.  To involve the audience, tell the audience to lean collectively to the right and say ooh when the solution turns dark blue. When the solution turns colorless, they should lean to the left and say aah. They can relax and sit straight up when it is briefly yellow. Be sure to let the audience know when they can stop reacting to the demonstration.

Mellow Yellow Reaction.  The narrative for these reactions is left to you but the audience can be told that you are trying to make a solution with a mellow yellow color but as you proceed, the colors keep getting darker.  It appears you will not be successful as how do you change from a dark solution to a yellow one?

Paper chromatography. Felt tip pens (try Vis a Vis wet erase felt tip pens) are used to spot a piece of Whatman #1 chromatography paper (or similar) cut appropriately (11 x 19.5 cm) to fit a 600 mL beaker. The paper is suspended with a large paper clip on a pencil. When water is used as the solvent, the separation is not complete but sufficient for students to see separation and differences between different colors and the same color of different brands. About 40 mL of a 1:1:1 mixture of 1-butanol, ethanol and 2 M ammonia works much better with some brands and the mixture seems to be stable for long periods of time. It does require more time for preparation and it smells. http://murov.info/EM-st6.pdf  http://murov.info/chemhome.pdf

HOME:  This experiment can be done at home with water, coffee filter paper and food coloring or appropriate pens.

Molecular Motion. A drop of food coloring is added to tall 200 mL beakers containing room temperature and very hot water.  Discussion of the experiment centers around molecules and molecular size and motion. Models of molecules such as water, butane, aspirin, penicillin G, and ampicillin ( a very brief discussion of pharmacology can be brought in here with regard to the differences between penicillin and ampicillin and why chemists designed and synthesized ampicillin) are demonstrated. As a hint on the identification of aspirin, ask the students if they are always good at school or if they ever give their teachers headaches. Interesting answers are obtained if students are asked to compare the number of molecules of water in the beaker to the number in a balloon and to estimate the absolute number. Numbers given will usually be very low (sometimes starting at 3) until you keep telling them "higher". Be prepared to explain the meaning of googol and infinity. Solids, liquids, gases and molecular motion are also compared at this point.

Additional productive discussion is possible if a heater stirrer (without the word magnetic printed on the front) is used to heat the water.  The audience members are asked to explain the stirring mechanism of the stirrer. http://murov.info/EM-st14.pdf   Even if it is carefully explained that the heating and stirring mechanisms are independent, someone will answer that the stirring is caused by the heating. Others will say vibration and still others, before the word magnet comes out, will say the white stirrer is a piece of chalk (but would chalk go around?). The reason for the plastic coating on the magnet can also be discussed and some students say it is there to trick them. One fifth grader even came up with an innovative application for the stirrer: "I liked the jar where you make a whirlpool. I wish I had one of them. My dad would mix Martinis with it." It is also possible to bring some chemical engineering into this by asking what properties (melting point, inert) the white plastic should have and can they think of a plastic with the desired properties.

HOME:  With parental help (pouring the hot water), this experiment can be done at home.

pH Indicator.  Several similar instructions for the preparation of universal or Yamada indicator exist.   One of the most common follows:

To prepare 1000 mL indicator, dissolve the following amounts in 500 mL ethanol:
0.025 g Thymol Blue, 0.060 g Methyl Red, 0.300 g Bromothymol Blue 0.500 g Phenolphthalein.
Neutralize the solution (to green) with 0.05 M NaOH and dilute to 1000 mL with water.

The approximate resulting colors are given in the figure to the right:

Depending on the audience size, add several drops of the indicator to water.  Use of a magnetic stirrer facilitates the demonstration. Now add 0.05 M HCl dropwise until the solution turns reddish.  Add 0.05 M NaOH dropwise with mixing to take the solution slowly from red too orange to yellow to green to blue to dark blue.  This process can be repeated back and forth as many times as desired.

HOME:  To prepare an indicator at home that will display a few colors at different pH values, place several leaves of red cabbage leaves in a small pan and cover with water. Bring water to a boil and immerse filter paper (some coffee filter papers will work) into the now purple colored liquid. Allow the paper to dry and test with different solutions.  Alternatively, several drops of the cabbage juice can be added to a solution.

Templates 2 and 3 for 8.5 inch x 11 inch
chromatography paper are on next pages.

 fic

     2.  Sink or Float? 

Many years ago, David Letterman had a popular segment on his late night show that asked the question, Does It Sink or Float?  Several easily demonstrated examples surprise many audience members and can help people understand the concepts involved including the crucial role of density.  Density is the ratio of the mass to the volume.  For an object to float, the density of the object must be less than the density of the liquid.  For objects such as boats, the whole volume of the object needs to be used.  This is the reason that steel ships despite the much larger density of steel than water have an overall density less than the density of water and float.

Colas and diet colas.  Ask the audience if cans of cola and its diet variety (Coca Cola and Pepsi Cola both work) will sink or float.  They will be surprised that the regular cola sinks meaning that the mass of the can and contents divided by its volume is greater than the density of water (0.998 g/mL).  The diets float and the question is what is the difference.  Since artificial sweeteners are about 200 times sweater than sugar, much less sweetener is needed and the diet can weighs less than the regular resulting in a density less than the density of water.  If desired, this demo can be used to emphasize one of the many advantages of the metric system over the American system.  What is the density of water in lb/pint?

Density is a very important physical property that like melting points and boiling points is very useful for identification purposes.  These properties have a very important attribute in common, none depend on the amount of substance present.  1 gram of a substance has the same melting point and density as a ton of the substance.  Density generally requires measurements of both mass and volume.  However, there are tools that are calibrated in density units such as a hydrometer which can be used to determine the density of car battery fluid (is the battery still useful?) and car radiator fluid (how low can the temperature go before it freezes?).  Density is a very important property used for the selection of materials.  For example, the density of aluminum is less than half of that of iron.  Other properties such as strength and corrosiveness might also have to be considered.   Titanium with a relatively low density and high strength might also be considered but price might be a deal breaker.

Bowling balls.  Ask an audience if they think a bowling ball will float or sink.  The answer is that it depends on the mass of the bowling ball.  Standard 16 lb bowling balls are denser than water but bowling balls that weigh less than about 11.5 lbs (5.27 kg) will float.  Bowling balls are available that weigh less than 11.5 lbs.

HOME:  Math problem.  A standard bowling ball has a diameter of 8.50 inches. Ignoring the finger holes, what is the maximum mass in lbs and kg that a bowling ball can have and still float in water at 20^oC?

Water and Ice.  A very common sight is a container with ice and water.  Most have observed that the ice floats in the water.  Millions of substances have been characterized (some properties determined) by chemists. Of the millions, it is interesting and astonishing to note that almost all of us have seen the liquid and solid phase of the same substance in the same container only for the substance, water. In other words the question of whether the solid sinks or floats in its own liquid is observed by most for water only. As a result, the behavior of water is accepted by most as the norm. However, think about this. As the liquid condenses, it should contract in volume until it freezes where further contraction is intuitively expected. Thus the solid is expected to be denser than its liquid and sink in the liquid. Except for water and a few other substances (including the elements silicon, germanium galium, arsenic and bismuth), this expectation is realized and the solid sinks in its liquid state (consider what would happen to lakes in the winter if water behaved like almost all other substances).  Observation is the key to good science. A good observer would ask the question why does the ice float but very few of us have asked this question and we need to learn to make more complete observations. The question why ice floats in liquid water (why ice is less dense than liquid water) is a difficult one but water molecules are closer together in the liquid state than in the solid state   For more information, please visit:  http://murov.info/EM-st1.pdf .  To demonstrate that water is unusual, the easiest comparison is to place ice in water and p-xylene in another test tube.  Place the p-xylene test tube in an ice water bath for a few minutes and scratch the inside of the test tube with a glass rod.  Some of the p-xylene should freeze and the solid as contrasted with the water test tube should sink.  Other substances can also be used but p-xylene is preferred.

Extension:  Try many other household items.  Ask the audience before testing whether the item will sink or float.  Suggestions:  apple, orange, avocado, raw potato, baked potato, hollow steel ball and solid steel ball.  It is also interesting to pass out a small ball bearing, a rubber stopper and a cork ring and ask the audience to rank them by increasing mass (see:  http://murov.info/EM-st7.pdf ).   While this hands-on exercise is not about density, it does demonstrate that we have to be careful with preconceived notions.  In this case, the hand probably perceives pressure or mass/area².

Rate of Falling:  Although it has been demonstrated that the rate of falling in a vacuum does not depend on the mass or density of the object centuries ago, it is likely that many people think that mass does influence dropping rate.  To definitively demonstrate this would be difficult without extensive instrumentation, the dropping of two same sized plastic bottles, one filled with a dense substance such as iron or lead and the other empty, should appear to hit the ground simultaneously if dropped from about 5 feet.  The density of the empty bottle is much less than the density of the filled bottle but within observational limits, the two bottles fall at the same rate.  For more information on this probably counterintuitive concept, please visit: The legend of the leaning tower – Physics World  and Galileo's Leaning Tower of Pisa experiment - Wikipedia

HOME or  in group activity:  Aluminum boats.  Each participant is given a 6 or 8 inch square piece of aluminum foil.  The aluminum is folded as desired to make a boat.  The boat is floated in a tub of water and the number of pennies needed to sink the boat is determined with the most pennies added determining the winner.

3.  Hot or Cold? 

Liquid Nitrogen.  Liquid nitrogen is available in many locations but for most presenters, requires the extra effort to get it (compressed gas sources sometimes stock it).  For occasional use, a 4 Liter Dewar is recommended (available for $100 to $1000).  If presentations are given frequently, a larger container such as a 40 liter Dewar is suggested (around $1000).  The price of the liquid nitrogen will vary with the source but should not be more than $5/L.  The presentation can be started out by stating that a mysterious substance in the vacuum flask will be used for several experiments during the course of the presentation (about one every 10 minutes). The students are asked to remember their observations and hopefully deduce the properties (is it hot, room temperature, or cold, is it solid, liquid or gas, is it colored or colorless) and the name of the substance by the end of the program.

1. A balloon is attached to a piece of vacuum hose with a hose clamp. The other end of the hose is connected to a plastic bottle containing a small amount of liquid nitrogen.
2. An inflated sealed balloon is slowly pushed into liquid nitrogen. Balloons that have bulges or twists are more interesting. After the balloon has shrunk to a minimal size, it is allowed to warm to room temperature. For college audiences, ask why the volume decreases to close to zero rather than about 1/4 of the volume as predicted approximately by Charles’ Law.
3. After liquid nitrogen is added to a plastic bottle, a rubber stopper is securely inserted into the bottle.  After several seconds it will shoot out into the audience if aimed properly.
4. Into the plastic bottle containing liquid nitrogen, insert a rubber stopper with a 25 cm long piece of 7 mm tubing that reaches to near the bottom of the bottle. A fountain will result and if sufficient nitrogen is used, it is possible to almost disappear in the descending fog. The rubber stopper should be held carefully as on rare occasions, liquid nitrogen runs down the glass tube and can freeze small portions of your fingers.
5. A marshmallow (or many other interesting objects) is placed on a copper wire and inserted into liquid nitrogen. After about 3 minutes, gentle tapping in a beaker will shatter the marshmallow.  One alternative is to smash the marshmallow with a hammer.
6. Liquid nitrogen can be harmlessly poured quickly on the back of your hand for very short periods of time.
7. Have the children separate if the floor is carpeted and leave a wide aisle and throw some liquid nitrogen onto the floor between them.

After seeing the marshmallow, students will respond with great enthusiasm if you ask them if they want you to put your hand in the liquid nitrogen and bang it on the table (don't do it but as indicated above you can pour a small amount carefully onto the back of your hand). One student wrote: "Next time you make an icemallow, taste it and tell me what it tastes like. But if it's poisonis and you die don't tell me. If you ever shater your hand in liquid nitrogen, I hope you have some glue with you." Students have a difficult time grasping the liquid air concept as they do not generally understand the solid, liquid and gaseous states. The system can be related to ice, water and steam but difficulty is still encountered. The teachers should probably discuss the liquid nitrogen demonstration in detail in their classrooms.

4.  Sound, Light and Space

A vacuum pump is needed for these demonstrations but relatively inexpensive ones that should be adequate are available under $100 from sources such as Harbor Freight.  Also needed is a plastic bell jar.  These are available over a big price range but a reasonably sized one should be available for under $200.

 Experiments in the vacuum chamber are used to demonstrate the effects of a vacuum on marshmallows, slightly inflated balloons, shaving cream and sound. sources. 

1.  Slightly inflate and tie off a small balloon and suspend it from the top of the chamber with a short piece of tape.  Evacuate the chamber.  The audience is asked to name 3 methods of inflating a balloon (adding a substance such as air or water to the balloon, heating the balloon, removing the air from the exterior of the balloon).  The third reason is not trivial for some people to understand.  If the balloon has been inflated properly, it will eventually pop but the sound intensity will be much less than if air had been in the chamber.  If the audience is asked to give their observations, seldom is the intensity of the popping mentioned.  The importance of complete and unbiased observations can be discussed.  When asked why popping was relatively quiet, the most common answer is that the chamber insulates the sound.  While this does have an effect, it is a minor one compared to the fact that sound cannot travel in a vacuum.  A short discussion of sound follows with the audience asked to cover their larynx and talk and notice the vibrations.  A little sound is heard because the balloon is usually touching the side of the chamber.  Other experiments included below reinforce the inability of sound to travel in a vacuum.  It is also useful to compare sound waves to light waves.  With a clear and colorless chamber, the audience should be able to observe that light travels through the chamber.  A light source such as a flashlight can be used to emphasize this.  The relative speeds of sound and light can also be discussed.  To illustrate the point that light travels through a vacuum but sound does not, discuss the waves that reach us through a vacuum from the sun.  What kind of sound does the sun make?

2.  Insert 2 or 3 large marshmallows into the chamber and evacuate.  Audiences are even more fascinated if marshmallow shapes such as chicken or bunny Peeps are used.   The marshmallows expand substantially due to the trapped air and reach a maximum and then shrink back a slight amount presumably due to the popping of some of its cells.  When the air is readmitted to the chamber, the marshmallows shrink to a size much smaller than their original size.  Ask the audience if the marshmallows should be eaten at this point and many will say no primarily due to their appearance.  Although the texture has changed, the taste would probably not be significantly changed but a discussion of the safety of eating food that has been in a laboratory environment.

Mercury shadowgraph. ALERT Inhalation of mercury vapor is an extreme health hazard.  If this demo  is performed, the mercury  needs to be in a sealed container  that can  easily be opened for a very short period of time.  Fluorescence alone is demonstrated first using a pre-coated thin layer chromatography sheet with a fluorescent indicator. A short wave (254 nm) mineral light (or chromatography light) is a convenient portable light source. Next, a shallow plastic bottle of mercury is opened and placed between the light and the fluorescent screen. In a sufficiently darkened room, the shadows of the mercury vapor are easily observed on the screen. A little blowing on the mercury sometimes enhances the demonstration. While the  amount of mercury  vapor  visible cannot  be estimated from the observation, it  is clear that  the mercury is evaporating at an alarming  rate (but only about 1/10,000 the rate of water evaporation).  Since the 254 nm from the mineral light is a mercury emission line, it exactly matches the absorption line of the mercury vapor.

Electric Pickle. This experiment should be performed in a well ventilated area or for a very short time only. Cut off the female end of an inexpensive extension cord and split the wires. Solder large sheet metal screws to each of the wires. Support a large dill pickle in some way that won't require touching (we use a ring stand and a clamp) and insert the sheet metal screws into opposite ends of the pickle. Plug the cord directly into a multiple outlet with an on off switch and after several seconds smoke should start coming out of the pickle and shortly thereafter, it should start glowing (and burning and giving off a nasty odor). At this point, the lights should be turned out but remember to run this for a short period of time and be very careful not to electrocute yourself. Students should definitely be cautioned not to try this one at home. It is possible to use several pickles simultaneously and use them on a Chemistree.  (S. L. Murov, J. Chem. Ed., 71, 1082 (1994).  "Chemistree" , A Chemistree | Journal of Chemical Education (acs.org)).

8.  Miscellaneous Demonstrations.

 Endothermic Reaction. Alert:  Barium is a very toxic ion and care must be taken with disposal.  Vials containing 20 g of Ba(OH)₂^.8H₂O. and 10 g of NH₄SCN (other less toxic chemicals can be substituted such as Sr(OH)₂^.8H₂O and/or NH₄Cl but the reaction is not quite as dramatic). The formation of water and frost can be observed and the presence of ammonia detected by smell. The flask gets cold enough (-20^oC) to condense moisture form the air. The condensation can be demonstrated by rubbing some of the frost on the flask exterior with a finger. Some students near the front can be allowed to touch the flask and tell the other students that it is cold. Some students assume all chemical reactions evolve heat and confuse the frost with steam. The flask gets cold enough to freeze water added to the bottom of the flask and the flask can be frozen to a smooth surface using ice as glue.    

The importance of the use of all the senses (except taste) can be stressed when the solids barium hydroxide octahydrate and ammonium thiocyanate are mixed. This endothermic reaction produces Ba²⁺, SCN^-, water and ammonia. Sometimes, I ask the students to close their eyes before I mix the chemicals and tell me what they think has happened just from the change in the swirling sounds. Students will quickly pick up the solid-to-liquid phase change and if you allow them a quick whiff, some will recognize the smell of ammonia. One student had some interesting spelling in the following comment: "Espally I liked when he truned some stuff into pneumonia." Note the correct spelling of the incorrect concept.

 Returning the to observations, most will not report the formation of frost on the exterior of the flask and about half say they think that the flask is hot (many associate chemical reactions with heat evolution). One can let them touch the outside of the flask, read an inserted thermometer (about -10^oC to -15^oC), and/or freeze an object to the flask by adding water externally. Discussion can follow on observations, the Celsius temperature scale (let the students invent it if they are not familiar with it), reaction energetics (including entropy if desired for high school groups, melting points and the effects of additives on melting points (why doesn't the material in the flask freeze if it is -15^oC?). The salting of roads in the winter and the preparation of ice cream and antifreeze mixtures for cars can be discussed.

Nylon. In a glass bottle, prepare a 0.25 M adipyl chloride solution in cyclohexane. Transfer about 20 mL of this solution to a plastic dropper bottle. In a plastic bottle, prepare an aqueous solution containing 0.5 M 1,6-diaminohexane and 0.5 M NaOH. Put about 2 mL of the amine solution in a shallow dish or watch glass.  Insert a  copper wire with a small loop at its end into the solution and slowly pull out the nylon.

Some references

Chen, P. S., Entertaining and Educational Chemical Demonstrations, Chemical Elements Publishing Co., 1974, 20.
American Flag Proportions, http://www.montney.com/flag/proportions.htm  (accessed 03/05/09).
For example, see: The National Anthem: The Star-Spangled Banner,
http://murov.info/NationalAnthem(U.S.).ppt
http://www.usflag.org/thenationalanthem.html  (accessed 03/06/09), The Star Spangled Banner
http://www.scoutsongs.com/lyrics/starspangledbanner.html  (accessed 03/06/09), Star Spangled Banner.

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