Crystals are solids that are formed from regular repeating patterns of molecules. One of the most spectacular crystal formations is sodium acetate. I made sodium acetate by using a procedure from instructables. It was interesting, but very time consuming, so purchasing a bottle of it maybe a better way to go. When sodium acetate, CH3–COO– Na+, is dissolved in a little water, the oppositely charged ions dissociate. If left undisturbed and cooled, the ions do not form crystals and the sodium acetate remains a liquid, far below its melting point. If disturbed, or a tiny sodium acetate crystal is introduced into the solution, the oppositely charged ions (CH3–COO– and Na+) form a solid crytal structure quickly. The process is exothermic, releasing heat energy, which explains why this process is commonly referred to as "hot ice".
I have always wanted to do the hydrogen gas/oxygen gas balloon explosion in class, but it isn't very practical or very safe. Once again Steve Spangler shows a much easier and safer way to do the reaction. Of course I had to try it myself and it works beautifully. Making the egg hollow is quite easy as shown here. The most common chemical reaction taught to middle school students is 2H2 + O2 ----> 2H2O. They rarely see it live though. They also have a hard time understanding that water gas is produced by this explosive exothermic reaction (the same chemical reaction that is used in the space shuttle main engines).
This is a new variation on my "Fire Hand" demonstration. I never did like the size of the methane bubbles that were produced, so I got an idea from a Mythbusters' segment on methane bubbles. They used a tube with many small holes to create the small methane bubbles. I decided to to do a variation of it using aquarium tubing. The result is a bigger handful of methane bubbles which means a bigger flame!
A major standard our students have to learn is the difference between elements and compounds. Compounds are substances that are made of two or more elements bonded together. The elements that comprise a compound have different properties when they are bonded together than when they are separated. Students have great difficulty with this. I introduce the unit by doing a simple activity on mixtures. Educational Innovations sells a simple Mixture Separation Challenge kit. Students are first forced to separate the mixture into 3 groups. Students usually use the simplest property of color to do it. There are other properties such as relative density or optical properties (opaqueness, transparency, etc.). The main idea is that the substances can be separated by their properties, because those properties do not change when forming a mixture, unlike when a compound is formed.
I found a new way to teach the conservation of mass/matter this past year. Previously I taught it by having steel wool (iron) react with oxygen. Since our periods are shorter this year, I couldn't really do that reaction anymore. Now students mix heavy whipping cream and vinegar in an open system. The vinegar reacts with the casein proteins in the heavy whipping cream to form a solid cheese-like substance (basically it is cheese). It's not a very glamourous reaction, but is also a way to teach students about precipitation. Students have a difficult time understanding the concept of two liquids reacting to make a solid. This is a simple way for students to visualize that type of chemical change.