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I made ScienceFix.com to share my favorite demos that I do in my middle school science classes.  

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Entries in video (91)

Thursday
Jun182009

Video Demo: Grain Silo Explosion

BubbleShare: Share photos - Easy Photo Sharing This is a very popular demo in science classes around the country. You need a coffee can with lid, candle, and irrigation tubing (slide 1). You can use cake flour, corn starch, or lycopodium powder. Put some of the substance into a petri dish. Light a match and place the flame next to the substance. The substance will brown but it won’t ignite. Place the substance into the coffee can next to the tube (use a drill to make a hole near the bottom of the can so the tube can fit). Light a candle (the best kind are the flat votive kind) and place it opposite the hole (slide 2). Put the lid on the can and make sure it is snugly fit. Take in a deep breath, then place the tube into your mouth and exhale a big breath. An small explosion will happen causing the lid to fly off. This demo demonstrates that for a substance to ignite it needs oxygen. When the substance is packed together there isn’t enough oxygen that surrounds the particles and ignition can’t occur. By blowing into the can the substance spreads apart, increasing the surface area, causing the ignition and the reaction happens very quickly.

Precautions: Wear goggles. Try this demo ahead of time to make sure it works safely. Make sure students are at a safe distance.

 

Sunday
Jun142009

Video Demo: Burning Iron

Many of the demos that I use in teaching chemical reaction are taken from a terrific book called A Demo A Day–Chemical Demonstration Book. The book contains a year’s worth of chemistry demonstrations that are easy to follow and to use. This demonstration shows that when iron has a large surface area it can react with oxygen and burn easily. I first use the 9 volt battery and touch the ends to various steel surfaces. The students see that nothing happens. I then touch the battery to the steel wool (held by the clamp on the ring stand) and the battery provides enough energy to make the iron burn. The steel wool has a larger surface area than pieces of steel like the ring stand. The steel wool is exposed to more oxygen molecules. You can also use this as a conservation of mass demo. Simply place the steel wool in a plastic bag and measure the mass. After burning the wool (of course it shouldn’t be in the bag at this point) return the leftover material back in the bag and mass it again. The mass should be the same (although it might be greater afterwards, since oxygen has now bonded with the iron.).

Preparations: You may have to soak the steel wool in acetone for 15-20 minutes to remove the outer coating, so that the steel is exposed. Take the wool out of the acetone and left it air dry.

Saturday
Jun132009

Video Demo: Disappearing Cup

Many of the demos that I use in teaching chemical reaction are taken from a terrific book called A Demo A Day–Chemical Demonstration Book. The book contains a year’s worth of chemistry demonstrations that are easy to follow and to use. This demonstration shows the concepts of polymers. Styrofoam is an example of a polymer. A polymer is made up of monomers. You can think of a monomer as a Lego piece. When you connect the Lego pieces together you have a polymer. You can take a Styrofoam cup and place it in a petri dish of acetone. Push down on the cup and the cup seems to disappear! The acetone is breaking the bonds between the monomers.

Precautions: Acetone is flammable and needs to be used in a well ventilated area. Wear goggles.

Watch the Google video.

Thursday
Jun112009

Video Demo: Glowing Penny

Another great demo from the Demo a Day: Chemistry Demonstration Book. To get chemical reactions started activation energy is needed. During a chemical reaction, heat energy is often released (exothermic) or absorbed (endothermic). To get this reaction started, a pre 1982 penny is heated over a Bunsen burner. The penny is wrapped in copper wire and held over the flame with tongs. Once the penny is heated, it is then placed into the 125 ml flask that contains a small amount of acetone liquid at the bottom. The penny does not touch the acetone, but is just above the surface. The copper in the penny reacts with the acetone fumes to produce a very exothermic reaction where the penny glows. The penny will continue to do this for several minutes.

Preparations: Make sure you adjust the penny and the copper wire so the penny just sits above the acetone. Do this before you heat the penny.

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Wednesday
Jun102009

Video Demo: Diffusion

See 2 video demonstrations of diffusion in action. The first video shows a drop of food coloring diffusing through water. It is a video that is time lapsed at 1 frame/15 seconds. The second video shows a Ziploc bag of iodine placed into a beaker of starch water. It is a video that is time lapsed at 1 frame/30 seconds. The iodine diffuses out of the bag and into the starch water. Where the iodine is diffusing the starch water turns a dark blue.