Demonstrations
I've listed the Demonstrations below according to the primary chemical principle I've used them to illustrate, but many can be used in different ways at different times of the year. I sometimes use a demonstration just to liven up a slow day.
Here is a handout I made for a presentation at the 2009 Minnesota Science Teachers Association called "Making Chemistry Fun with Common Products." It includes several of the demonstrations described below.
Beginning of the year
Edible Candle. The edible candle is a piece of mozzerella string cheese cut in half. Make a wick by cutting a slit in one end and inserting a sliver of almond. Tell the class it is time to observe a “burning candle.” Light the almond "wick." Then blow out the flame and take a bite.
Chemical Foundations
Snap bead molecular models. Use large toy snap beads to illustrate the difference between pure substances and mixtures, and between elements and compounds.
Atoms, Molecules, and Ions
Oxidation states of iron. Fill a 1000-liter beaker about 1/3-1/2 full with an iron fortified cereal (like Wheaties). Crush the cereal somewhat. Add water to about 800 mL. Add a Teflon coated stirring bar. Put the beaker on a stirring motor and get the slurry to slowly stir. Leave the slurry stirring for at least 15 minutes. When the magnet is removed from the slurry, it should be slightly coated with fine iron filings. The longer the slurry is stirred, the more iron. It shows that the iron in cereal is elemental iron. I used this demonstration to emphasize the difference between elements, specifically metals, in element form and compound form.
Bonding
Balloons to demonstrate tetrahedral geometry. Have students help blow up 4 good quality round balloons. When you wind the knots together, the balloons assume a tetrahedral orientation. (I'm told you can use 6 balloons to form an octahedron but I have trouble tying that many balloons together.) If you make 2 balloons one color, and 2 balloons another color, you can also use them to show that the "molecule" formed is asymmetric. Save the balloons to demonstrate polymer properties.
Organic Chemistry
Polymer properties. When you are finished with the balloons used to show molecular geometry, a fun way to discard them, is to show that you can put a pin in the balloon without breaking it. Dip the pin in Vaseline and insert it slowly into the thick part at the bottom of the balloon. The balloon will not burst. Then withdraw the pin and insert it quickly into the side of the balloon to make it burst.
Paperclip polymer. To demonstrate the structure of a copolymer, link colored paperclips together so that the colors alternate. Make it into a “magic trick” with loose paperclips.
Superabsorbant polymer in disposable diapers. Cut open a disposable diaper in a gallon ziplock bag. Free as much polymer as possible from the cotton fluff (it feels like a crystalline solid). Discard the cotton and plastic, leaving the crystalline polymer in the bag. There should be at least ½ teaspoon. Add water (amount depends on the amount of polymer you've obtained, but start with 100 mL) to the bag and watch the beads of polymer swell. Choose a diaper brand that says "extra absorbant."
Charcoal filters. Put a cone of filter paper in a funnel in a 250 mL Erlenmeyer flask. Put a scoop of activated charcoal in the filter. Activated charcoal adsorbs aromatic compounds. Make a solution that has food coloring plus vanilla, peppermint or wintergreen. Pour a small amount of the colored/odored solution through the charcoal filter and it should come through clear, colorless and odorless. Pickle juice and red cabbage juice also work. This shows that the colors and flavors used are aromatic hydrocarbons. As a “control,” you can filter a CuCl2 or FeCl3 solution to show that the activated charcoal doesn't filter all "color."
White glue slime. Pour about 15 mL white glue into a small paper cup. Add an equal volume of water (about 15 mL), a drop of food color (if desired) and mix thoroughly with a wooden stick. Add about 10 mL (two tsp) of a 4% borax solution and stir. (If the slime is too watery, add more borax solution, 1/2 teaspoon at a time. Be careful, too much borax will make the slime too stiff.) Use the stick to remove the blob of slime and store in a zip-lock sandwich bag. (I use Borax detergent from the supermarket. One tablespoon Borax in one cup water is approximately 4%.)
Gases
Collapsing cans. Put a small amount of water in a soda can. Holding the can with tongs, heat it over a bunsen burner for several minutes after the water has begun to boil in order to replace as much air as possible with steam. As quickly as possible invert the can into a bowl of water. The can should collapse, producing a loud noise. It is now ready for recycling. I use this to demonstrate air pressure. I also do this demo in the beginning of the year when I ask the students to explain what is happening to the water as it is being heated. I have also been known to do this demonstration at any time to liven up a class.
Thermochemistry
Burning dollar. Make a 50% alcohol solution by diluting rubbing alcohol (usually comes as 70%) or from denatured ethanol. Immerse a dollar bill completely in the alcohol solution. Put away the alcohol solution. Holding the bill with tongs, light it with a match. The alcohol will burn off but the dollar remains intact due to the presence of the water. (If even a small amount of the dollar remains dry, it will burn. Be careful to keep the alcohol solution far away from any flame.)
Liquids and Solids
Water & oil bottles. Fill a clear plastic bottle about ½ full with salad oil. (I use "bottled water" bottles.) Add a drop of food coloring and fill to the top with water. Close tightly. Mix the liquids by inverting the bottle. This shows “like dissolves like” as the food coloring will only dissolve in the water.
Oxidation and Reduction
Ripping a soda can. Using a file, score a horizontal line around the inside of a soda can. Pour a solution of 1 M CuCl2 into the can and leave for 3-4 minutes. Pour out the CuCl2 and rinse the can. (The same CuCl2 solution may be reused for many cans.) Tell your students they make you so mad, you can rip a soda can in half. After you rip the treated can, you can let them see if they can repeat the feat with untreated cans. The inside of soda cans are coated with a thin layer of plastic to prevent the acid drinks from eating away at the can. The file cuts through the plastic coating and the CuCl2 etches a ring around the can, making it easy to rip in half. Do this demonstration when teaching oxidation-reduction reactions. Be careful as the edges of a ripped can are sharp.
Acids and Bases
Indicator Sponge. This is a demonstration from Flinn Scientific. A red sponge turns blue in a red solution. Putting the now blue sponge in a blue solution turns it back to red. You can either buy the sponges from Flinn in a kit or the demonstration link tells you how to make them yourself.
Disappearing Rainbow. This is a demonstration from Flinn Scientific and is pictured at the top of this page. You can buy the demonstration from them as a kit. The demonstration link describes the demonstration and tells you how to prepare the solutions yourself from mixtures of three indicators that are colorless in acid.
Anytime
White glue slime. Pour about 15 mL white glue into a small paper cup. Add an equal volume of water (about 15 mL), a drop of food color (if desired) and mix thoroughly with a wooden stick. Add about 10 mL (two tsp) of a 4% borax solution and stir. (If the slime is too watery, add more borax solution, 1/2 teaspoon at a time. Be careful, too much borax will make the slime too stiff.) Use the stick to remove the blob of slime and store in a zip-lock bag.
Collapsing cans. Put a small amount of water in a pop can. Holding the can with tongs, heat it over a bunsen burner for several minutes after the water has begun to boil to replace as much air as possible with steam. As quickly as possible invert the can into a bowl of water. The can should collapse, producing a loud noise. It is now ready for recycling.