Demonstrations
These demonstrations are generally for middle school students, but have applications for both younger and older students. If chemicals are being used check the MSDS sheets or wear goggles, apron and gloves in a well ventilated area.
PRIOR PRACTICE PREVENTS POOR PERFORMANCE
Why do demonstrations? to display chemical or physical properties.
What makes a good demonstration?
- one that fits the topic.
- one that catches a persons interest, usually through surprise.
- one that shows the concept clearly.
- visible.
- one where the student has to come up with the answer after the demonstration is performed.
For spontaneous combustion make a small pile of finely ground potassium permanganate (KMnO4) with a depression in the middle. Pour glycerine into the depression. An exothermic (heat given off) reaction will take place. Be sure to wear safety equipment.
- Burning dollars. Soak a dollar bill in equal amounts of water and alcohol (ethanol from a drug store or chemical supply company). Hold the damp dollar with tongs and set on fire. The water will protect the dollar while the alcohol burns off.
- Egg into a bottle. Use a bottle with an opening slightly less than the hard boiled eggs diameter. Put burning paper into the bottle and immediately put a peeled, hard boiled egg on top. The burning of oxygen in the bottle will reduce the pressure inside allowing the outside air pressure to push the egg into the bottle. This can also be done with a peeled banana. To get the egg out turn the bottle upside down, cover the opening with your mouth and blow into it.
- Density experiment (#4-7). Using food coloring mix up hot green water in one glass. Into another glass mix up cold red water. Pour the cold water slowly down the inside of the tilted hot water glass. Observe. Try it again with the hot water poured into the cold water. Next make up colored water and a very salty water solution of the same temperature. Again pour slowly down the inside of the tilted glass. Next put a golf ball into the salt water and another golf ball into regular water. What does this tell you about the golf balls? Try the golf ball or other balls in various liquids.
Sinking ice cube. Put a regular ice cube into alcohol instead of water.
- Can-tank-er-us. Get room temperature cans of cola with sugar and diet cola. Put them into an aquarium of room temperature water. The can with sugar should sink and the diet one should float. If floating does not occur use colder water in the aquarium. If you open the can of soda and evaporate off the liquid you may be surprised how much sugar will appear.
- Density (wave) bottle. Put the following into a clear liter bottle: equal amounts of alcohol (rubbing or ethanol), water with food coloring, and kerosene. Screw on the cap and tape shut. Slowly rock back and forth.
- Dippy bird. Follow directions and try to figure out how it works. Evaporation of water from the bill causes coolness there. As a result the air pressure inside the birds head is reduced which pulls up the liquid from the bird's bottom. The liquid weight up high causes the birds head to drop and the liquid escapes to run back into the bird's bottom. The birds head comes up.
- Can crusher. Take an empty soda can and rinse the inside with water. Dump out the excess water. Heat the can until steam is seen. Using tongs, lift the can and put the open end about 1/4 the way into a container of water. The can will be crushed by outside air pressure.
- Water lifter. Take an empty and strong glass bottle and rinse the inside with water. Dump out the excess water. Heat the bottle in boiling water. Wearing goggles, gloves and an apron use tongs to lift the bottle and put the open end about 1/4 the way into a container of cool water. Water will be lifted inside the bottle because of the reduced air pressure there.
- Attach cotton cheesecloth over the opening of a glass (baby food jars work best). Slowly pour water through the cheesecloth into the bottle. Turn the bottle upside down. Observe. This can also be done with a piece of cardboard by filling the glass with water, sliding the cardboard over the top, holding the cardboard in place while you flip the glass and cardboard upside down and then removing your hand from the cardboard.
- Exploding bubbles. Into a plastic washbasin put warm water and detergent (Joy works well). Using an unlit propane torch blow gas into the water to form bubbles. Remove the torch and light it away from the bubbles. Pass the burning torch over the bubbles and observe. The black particles are carbon. WARNING: You may damage your hearing if an oxy-acetylene torch is used.
- Dry ice. With gloves or tongs put the dry ice into a balloon and close the opening. After all the ice is gone pop the balloon.
Wearing gloves hold a piece of folded cardboard with a chunk of dry ice in it and tilt it down to allow the gas to flow toward the base of a flaming candle.
Take some Kool-Aid or other syrup mix and make it according to directions. Fill a glass with the mix and drop in a piece of dry ice. You will carbonate your beverage.
Cover a section of rubber hose with dry ice. After most of the ice has disappeared hit the rubber with a hammer.
- Lift an ice cube without touching it. Place an ice cube in a container of water. Provide a string and some salt. The person cannot touch it with their body. To do it, put the damp string across the ice cube and pour salt on top. After a few minutes the string will be frozen to the ice cube and the cube can be lifted carefully with the string.
- Hot pack/Cold pack. The heating or cooling effects of hot or cold packs is due to ionization and not a chemical reaction. This is a physical change.
Heat packs contain 40 g of calcium chloride or magniesium sulfate per 100 ml of water. The chemical is kept separated from the water until heat is needed. The temperature will rise to about 90 degrees F and last for 15 to 30 minutes. Heat packs are used by people who are outdoors in cold weather such as fishermen, skiers, etc.
Cold packs contain about 30 g of ammonium nitrate per 100 ml of water. The temperature will drop to around 32 degrees F and last for 15 to 30 minutes. The cold pack would be wrapped in a towel before being applied to the injured body part of an athlete. Why? What is the advantage of a cold pack over using ice? How long should cold be used on an injury before switching to warmth?
- Incredible Shrinking Peanut. Put acetone from a hardware store into a glass, ceramic or metal container. Put styrofoam cups or peanuts into the acetone and watch them shrink. If you process a lot of styrofoam you will get a hard plastic on the bottom which can be washed with water and it's properties observed. If the peanuts will not dissolve then they may be starch and they will disappear in water.
- Colors during burning. Put 1 pound of Epson salt (white flame) or Borax (green flame) or no-salt substitute (purple flame) or table salt (yellow flame) into 1 gallon of water in a 5 gallon bucket (like a sheet rock compound pail). Stir and dissolve the chemical while wearing goggles and rubber gloves. Put in pine cones or thin strips of dried wood (like pine) and let them soak for a day. Take them out and let them dry outside on old newspaper to protect concrete, etc. Burn in a fire and watch the colorful flames.
A great source for experiments are the books by Bassam Z. Shakhashiri called Chemical Demonstrations. These can be ordered from the University of Wisconsin Press, 114 N. Murray Street, Madison, WI 53715. Back to top
