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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 (90)

Wednesday
Aug052009

The Reverse Balloon

One of my all time favorite demos. This is a variation on the crushing of the soda can via atmospheric pressure. I do this demo when studying the phases of matter. The molecules in a gas are rapidly moving in all directions and they are spaced as far apart as possible. When cooled to a liquid phase, the molecules come together as close together as possible thus taking up less space. This demo illustrates that.

Fill the 250 ml flask with about 50 ml of water. Set the flask on the hot plate and heat until water boils. Carefully take the flask off the hot plate with tongs. Carefully (don’t get burned) stretch the opening of the balloon over the mouth of the flask. Then with tongs, carefully transfer the flask so that the bottom half sits in ice water. Watch what happens!

The gaseous water in the flask quickly turns to the liquid phase. The molecules in the liquid phase take up much less space (volume) and the balloon gets pushed (sucked) into the flask and stays that way. Your students will be amazed.

Sometimes I show the end result to them first, and they are then challenged to test ways in which it can be done.

Precautions: Use tongs in this demo. The flask gets extremely hot.

Friday
Jul312009

Video Demo: Boiling Points

Three liquids (oil, isopropyl alcohol, and water) are placed on a hot plate. Over time all of the isopropyl alcohol boils away, half of the water boils, and none of the oil boils. This demonstrates that isopropyl alcohol has the lowest boiling point, followed by water, and oil has the highest boiling point. I show my students this video as we learn about phase change, and the properties of matter (boiling point, melting point, etc.). I ask my students the following questions after the video.

 1. Which liquids boiled?
2. Where did the lost liquids go?
3. The temperatures 78 degrees C, 100 degrees C, and 204 degrees C are the boiling points for the above substances. Match the boiling point temperatures to the substance.
4. Which would hurt more if one of these were to touch your skin: boiling oil or boiling water? Explain.
5. Explain why oil is used to fry foods instead of water (like potatoes, fish, etc.). Hint: look at their boiling points.

Wednesday
Jul292009

Video Demo: Carbon Dioxide Extinguisher

This video demonstrates some of the properties of carbon dioxide gas. Carbon dioxide gas is more dense than air. The gas can be poured kind of like a liquid. The video shows carbon dioxide gas being poured to extinguish a candle flame. A candle flame needs oxygen gas to burn. Since carbon dioxide gas is surrounding the flame, the lack of oxygen gas makes the flame go out. You could also use dry ice as a source of cargon dioxide instead of vinegar and baking soda.

materials needed

large poster board folded

video

Monday
Jul272009

Video Demo: Reaction Chamber

This is a demo that I only show the video. This is an example of what happens in the reaction chamber of a liquid fuel rocket. I use about 100 ml of denatured alcohol. I pour it into the 5 gallon plastic bottle. I swirl it around vigorously, trying to speed up the evaporation of the alcohol. I pour out the excess liquid alcohol. I then set the bottle on the counter, making sure it is flat. With a candle attached to the end of the meter stick, I insert the candle in the opening of the bottle. Again, I only show the video of this to my students and don’t do it live. It demonstrates the volatile reaction that occurs with oxygen in the air. The resultant hot gasses funnel through the opening (nozzle on a rocket) at a higher speed. This demo also shows when the particles of a chemical are spread out (increased surface area), the speed of a reaction increases.

ONLY TEACHER DEMO! I ONLY RECOMMEND TO TEACHERS THAT THEY ONLY SHOW THIS VIDEO IN CLASS AND DON’T DO THE DEMO IN CLASS. NEVER, EVER USE A GLASS BOTTLE! ONLY USE A PLASTIC BOTTLE.


Wednesday
Jul152009

Video Demo: Water Up

An inverted 100 ml beaker is placed inside a 400 ml beaker filled with colored water. The 400 ml beaker is placed on a hot plate. The water boils for a while, and then the beaker is removed. The water vapor inside cools condenses back into liquid. The molecules of a liquid take up less space than a gas, and therefore the pressure inside lowers. The atmospheric pressure pushes the colored water up inside the beaker. This demonstration can be found in Tik L. Liem’s Invitations to Science Inquiry.