I have seen demonstrations of atmospheric pressure and the gas laws performed by first heating water inside a container (like a solvent can or an aluminum can), and then closing the container and allowing it to cool. As the vapors inside the cooling container cool and condense, the pressure inside of the container decreases relative to the surrounding atmosphere and the container collapses. Instead of these metal containers, one could also simply heat a water source like food inside a plastic container in a microwave oven while the lid is placed loosely on the container. As the contents of the container start to cool, the lid can accidentally seal onto the container, and the plastic container contracts. This is a phenomenon many people have observed, lending itself to discussions of gas properties.
Saturday, August 24, 2013
Friday, August 23, 2013
Photobleaching Construction Paper with Fluorescent Lights
I took down an old Bradley University Chemistry Club bulletin board and was impressed how, over the course of years, light from the fluorescent lights in the hallway in Olin Hall had penetrated thin copy paper (upper sheet in picture) and bleached the underlying construction paper from blue to gray (lower sheet in picture). I was also impressed how ink on the paper had slowed that process sufficiently that the printed ink on the copy paper left an image on the construction paper.
Sunday, August 18, 2013
Armored Mud Ball
I just learned over the last year what armored mud balls were (balls of mud that are rolled by moving water over stones, which stick to the surfaces of the balls) and how they have been found associated with the Kankakee torrent here in Illinois: http://books.google.com/books?id=cPfw7aIlowIC&pg=PA158&lpg=PA158&dq=armored+mud+ball+kankakee+torrent&source=bl&ots=Rp44nRB-4p&sig=8cV05df3PEM_MenwDzPRPgllykA&hl=en&sa=X&ei=a4URUpbsGaWIyAH9v4HICw&ved=0CC0Q6AEwAA#v=onepage&q=armored%20mud%20ball%20kankakee%20torrent&f=false.
I was surprised to find an armored mud ball, presumably recently made, in a creek bed in Bartonville where I was fossil hunting. I saw a recipe for making a food analogy of the mud balls that was published by the National Park Service: http://www.nps.gov/badl/forkids/upload/Make%20an%20Armored%20Mud%20Ball.pdf. I am reminded of yummy nut-covered fudge balls that I have eaten around Christmastime.
I was surprised to find an armored mud ball, presumably recently made, in a creek bed in Bartonville where I was fossil hunting. I saw a recipe for making a food analogy of the mud balls that was published by the National Park Service: http://www.nps.gov/badl/forkids/upload/Make%20an%20Armored%20Mud%20Ball.pdf. I am reminded of yummy nut-covered fudge balls that I have eaten around Christmastime.
Friday, August 2, 2013
Measuring Magnetic Properties of Materials (Including Your Hand) with an Electronic Balance
featuring
contributions from Paul Lee and John Tian
All materials
display some magnetic properties depending on such factors as their electron
arrangement, temperature, and particle size/orientation. Three notable types of
magnetism displayed in matter are diamagnetism, paramagnetism, and
ferromagnetism. Diamagnetic materials have orbitals containing only paired
electrons; each occupied orbital contains two electrons in opposing spin states.
They tend to be nonmagnetic or slightly repelled by magnetic fields.
Paramagnetic materials have some orbitals with unpaired electrons, each
containing only a single electron with a single spin state. These materials are
attracted to magnetic fields, but their random unpaired spin orientations only
enable weak attractions. Ferromagnetic materials have unpaired electrons similar to paramagnetic
materials. However, the unpaired electron spins of the ferromagnetic materials are
aligned cooperatively in magnetic domains, which enable much stronger
attraction to a magnetic field than in simple paramagnetic materials.
It is possible to measure the
relative strengths of magnetic properties in materials with simply an
electronic balance (that should have draft doors and measure to tenths of
milligrams), a strong magnet (preferably a neodymium-iron-boron magnet), and
two polystyrene foam cups. This demonstration is based on that described in Ellis,
A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky; G. C.; Robinson, W. R. Teaching
General Chemistry: A Materials Science Companion; American Chemical
Society: Washington, DC, 1993.
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