Lee Marek, famous for his frequent appearances on the David Letterman Show, makes chemical demonstrations for the Chemistry Community. In some cases the demonstrations are too dangerous to perform in a normal classroom but can certainly be shown. Each demonstration exhibits common chemical themes that are readily transposable into classroom teaching units. For instance, when discussing atmospheric pressure in the classroom a simple demonstration is to crush a soda can using atmospheric pressure. Now you can integrate that demonstration with Lee's crushing of a 55-gallon drum using the same technique. There are also videos of the highly exothermic thermite reaction, an explosion of an ostrich egg using hydrogen gas, the redox reaction of magnesium and carbon dioxide, and other demos. Sharing these videos is an excellent way to add some pizzazz to your classroom safely.
DISCLAIMER: These are done in a Lab setting with all safety guidelines followed by an experienced demonstrator. You may not know all the necessary warnings and safety procedures to carry these out in a safe manner. Please do not try to do these demos on your own. The presenters assume no responsibility or liability for the information provided here. It cannot be assumed that all necessary warnings and procedures have been given in this video. It is expected that person (s) using this information will use proper techniques in the safe handling & disposal of the chemicals involved in these demonstrations. REMEMBER PRACTICE "SAFE SCIENCE."
In this demonstration, Lee melts a quantity of sodium chlorate, an excellent oxidizing agent, to provide the activation energy for a series of redox reactions. The species that are oxidized are the candy red hots, a gummi bear, and a pencil. For the first two species the sugar is rapidly and spectacularly oxidized. In the case of the pencil, the cellulose in the wood is oxidized generating a flame similar to that from a rocket engine.
The combustion of magnesium is a highly exothermic reaction. So exothermic that it can react with carbon dioxide as well as it reacts with oxygen. Consequently, it is possible to ignite magnesium turnings in a block of dry ice and observe the chemical reaction. The magnesium is oxidized and the carbon dioxide is reduced leaving magnesium oxide and carbon as the reaction products.
Normal atmospheric pressure is 14.7 pounds per square inch. If a partial vacuum is created inside a container, the atmospheric pressure can literally crush the container. In this video Lee heats a small layer of water at the bottom of a 55-gallon drum until it begins to boil. The drum is then closed and sealed. As the steam cools and condenses, a partial vacuum is created inside the drum. The atmospheric pressure then spectacularly crushes the drum.
Common disappearing ink is a blue solution made from thymolphthalein dissolved in water. Thymolphthalein is blue in a basic solution. In the presence of an acid the solution turns colorless. In this video Lee demonstrates this acid-base phenomenon by pouring a thymolphthalein solution on a student's shirt then changing its color with a carbon dioxide fire extinguisher. The same phenomenon is displayed using a large graduated cylinder of thymolphthalein solution and pieces of dry ice.
Soda pop is a mixture with a variety of components. For this demonstration the important component is the carbon dioxide gas that is dissolved in the pop solution. Henry's law denotes that the pressure of the gas determines the concentration of a gas dissolved in a liquid. Thus if the pressure is lowered, in this case by removing the sealed bottle caps and replacing them with caps that have a small hole in them, the gas is less soluble in the liquid. Furthermore, Boyle's law states that as the pressure of a gas is decreased the volume increases. Thus there is a dual effect of less solubility and decreasing pressure to cause a large volume change in the carbon dioxide's volume. Creating large numbers of nucleation sites, places where bubbles can form, can also increase the rate of the volume change. Many of us have done this unintentionally by shaking a can of soda before we open it. In this case, Lee places the soda bottles in an ultrasonic cleaning device that literally shakes the soda at a frequency many times greater than can be done by hand. The result is a spectacular change in volume.
The reaction of aluminum and iron oxide is a very exothermic reaction with a large negative free energy. Lee demonstrates this reaction first on a small scale using spheres of aluminum and iron then on a larger scale with a mixture of powdered aluminum and iron oxide.
Lee uses a four-foot tall glass tube and a source of methane gas to vividly demonstrate the typical operation of a Bunsen burner. Included are the conditions where there is too much gas and not enough air, a proper mixture of gas and air, and too much air and not enough gas. This last condition causes a flashback down the glass tube.
Pressure is defined as a force divided by an area. In this demonstration Lee shows that even a large force spread over a sufficient surface area can be harmless. Lee breaks a concrete block on one of his student's chest using a sledgehammer without causing harm.
Lee and two of his students demonstrate that methane is less dense than air and highly combustible. They generate bubbles of methane gas inside a soap solution. As the bubbles float to the ceiling of the room they are ignited with a candle producing large amounts of flame on the ceiling.
Lee fills an empty ostrich egg with hydrogen gas and then ignites the gas. Once the ratio of air to hydrogen gas reaches the proper proportions a large explosion occurs. Safety shields stop the sizable pieces of egg shell from impacting people and the camera.
Lee uses 2 parabolic reflectors to focus in on the idea that infrared radiation (IR) shows wave properties. At the focal point of one mirror is an electric heating coil. A piece of paper is placed at the focal point of the other mirror. The radiant heat or infrared radiation from the first mirror is reflected onto the other mirror and is collected at its focal point. There is enough heat transferred to ignite the paper.
Lee mixes zinc and sulfur and then adds heat to make them react, showing an example of a synthesis reaction. (In college chemistry, it belongs in the category of REDOX reactions.) A giant mushroom cloud forms.
At room temperature, the decomposition of hydrogen peroxide is relatively slow. The addition of a catalyst increases the reaction rate dramatically by providing a different potential energy pathway with a lower activation energy. Heat is quickly generated and water vapor goes up into the air 20 feet.
Large test tubes are used to show the meaning of precipitation. The equation is balanced. All three levels of Johnstone's components are used: macro or tangible, molecular or invisible, and symbolic. They are discussed and represented in this chemical change.
