The Styrofoam cup. It seems like a simple unitasker, one that holds liquids and is a good insulator. Why is it a good insulator and so light? Styrofoam is the the brand name that Dow Chemical uses for its version of polystyrene. Polystyrene is a polymer, which is a substance that is made up of repeated units, monomers, bonded together. What makes Styrofoam special is the process in which it is made. During the process, gas is blown into the polystyrene causing the material to be mostly empty space. The Styrofoam is very low in density becuase the mass of the polystyrene is contained in a larger area. It is a good insulator because the air spaces that make up the foam deters heat energy flow. The above video demo shows what happens when the polystyrene is dissolved in acetone. The polystyrene structure basically collapses and condenses, leaving a hardened, more dense mass.
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Indicators are chemicals that show what type of chemical reaction occurred. I decided to have some fun with some pH indicators--chemicals that signify if a solution is acidic or basic. In the video, 3 different pH indicators, bromothymol blue, phenol red, and phenolphthalein (and ammonia) are used. The solutions are in long plastic pipes whereupon Alka Seltzer tablets are dropped. The Alka Seltzer tablets react with the water to produce carbon dioxide gas. The carbon dioxide dissolves in water creating carbonic acid and thus making the solution more acidic. The color of the solution changes as a result. Later ammonia, a base, is added to show how the color changes when the solution turns basic.
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".
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!
Students in my classes have to determine if a substance has changed physically or chemically. In order to do that, they need to know if the properties of a substance has changed. We can look at many different properties of a substance such as color, density, boiling point, melting point, taste, texture, hardness, etc. One of the most exciting properties of matter is the color in which they burn. In the video above I show color flame candles and then show a demonstration of two different compounds, strontium chloride and copper sulfate, mixed with denatured alcohol, that produce large colorful flames.