What happens to hot and cold water when placed in room temperature water? What if the water is colored? Watch the video for a simple demonstration of the properties of hot and cold water.
Entries in demo (81)
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.
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".
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).