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 (92)


Video Demo: Flour Fireball

When chemicals burn, it is really a chemical reaction between the substance and the oxygen in the air. When substances do not get enough oxygen, they don’t burn completely. Below is a video of 30 ml of flour exposed to a flame. Only a small fraction of the flour burns, while the rest does not. The surface area of the flour is quite small and needs to be spread out.

If the flour particles spread farther out from each other, more oxygen will be able to react with them. The following demo does just that.

The three pictures below show the required materials.

Place the pie tin with candles on a chair so that the pie tin sticks out a few feet. The meter stick can be kept in place by placing a few books on it. Measure out about 50 ml of flour and place into the sifter. Stand on a chair and sift the flour so that it falls onto the candles. Caution: Wear goggles, lab coat (or apron), and keep flammable materials away. Have a fire extinguisher close by just in case. Do not use too much flour!


Video Demo: Colorful Water Electrolysis

In my class students learn about chemical reactions and also the difference between elements and compounds. Students learn that the 5 signs of a chemical reaction are: 1) color change 2) gas production 3) precipitation 4) temperature change 5) change in properties (smell, texture, taste, density, etc.) Students also learn that compounds are chemicals that have 2 or more elements bonded together, such as water. In this demonstration, students observe water undergoing a chemical reaction, and breaking apart into hydrogen and oxygen gas. This demonstration can be done on an overhead projector so that all students can view it easily. The materials needed for the demonstration are shown below.

This is a simple demo that doesn’t require any special equipment. As the electricity goes through the water, molecules of hydrogen gas and oxygen gas form at the separate ends. The bromothymol blue solution changes color only at one of the ends, indicating the gasses are not the same. More hydrogen gas bubbles appear on one of the ends as oxygen gas bubbles on the other end. This clearly indicates the ratio of hydrogen atoms to oxygen atoms in water is 2 to one. Tip: Dissolve some salt into the water to aid in electricity flowing through the water.


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.


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.


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