Why is the oil at cooler temperatures more viscous than the oil at higher temperatures?
Two vials of 5W-30 motor oil are turned upside down and back to illustrate their viscosity. The oil in the vial at right, exposed to -17 C temperature, is much more viscous than oil in the vial at left, exposed to +17 C temperature.
Do molecules with strong or weak intermolecular forces have greater viscosity?
Twenty-five marbles emptied from Erlenmeyer flasks into tubs represent molecules in a flowing liquid. Glass marbles in the flask at left have little interaction and represent molecules with weak intermolecular forces. Marbles containing magnets in the flask at right represent have magnetic attractions and represent molecules with stronger intermolecular forces. When both flasks are shaken at the same time, the flask at right takes longer to empty. The magnetic marbles in that flask have a greater resistance to flow and represent the liquid with the greater viscosity.
Why does the polystyrene shrink?
A polystyrene (recycling code #6) container lid is laser-cut into a graphene pattern, colored with permanent marker, and then placed into a toaster oven. The heat of the oven raises the temperature of the polystyrene above its glass transition temperature, enabling the polymer chains to mobilize and the polymer film to contract laterally, thickening in the process. When the polymer film is moved out of the oven, it cools down below its glass transition temperature and hardens in the shrunken form. Note that the film shrinkage is not always isotropic; here the hexagon shrinks more in one direction than others. Also, the shrunken graphene pattern can be rolled into a carbon nanotube shape while it is still hot out of the oven. Thanks to Thomas Kahila for laser-cutting these sheets.
Why do you think the room temperature liquid has bits of solid in it that don’t nucleate the solid growth?
These heat packs contain sodium acetate and water. When they are placed in boiling water, the heat causes the solid sodium acetate to dissolve. When the packet cools, the sodium acetate solution stays liquid. The packet contents stay liquid until a metal disk inside is flexed, which initiates the growth of solid sodium acetate crystals and generates heat in the process. What is confusing to me is that many times the room temperature liquid in the packet has bits of solid in it, yet these do not seem to nucleate the sodium acetate crystal growth.
How could you explain hole motion in a semiconductor using this model?
A tile puzzle can be used to model hole motion in a semiconductor. Each tile is marked with an "e-" as an electron, and behind each tile is marked with an "h+" as a hole. As an electron tile moves to fill the hole gap, the hole moves to where the electron had been. Thus holes and electrons migrate in opposite directions in a semiconductor. This sort of tile puzzle could also be used to also model ion migration in conducting salts.
What bands are able to conduct electricity?
Jars can be used to represent energy bands. Sand can be used to represent valence electrons. Jars that contain no sand or are completely full of sand cannot have mobile sand; jars that are partially full of sand can have mobile sand. Similarly, bands that contain no electrons or are completely full of electrons cannot have mobile electrons and do not conduct electricity; bands that are partially full of electrons can have mobile electrons and do conduct electricity.
What is the difference between plastic and elastic deformation in metals?
Portions of a polystyrene foam egg carton are used to model planes of atoms in this demonstration of elastic and plastic deformation in metals.
What is the difference between substitutional, interstitial, and amorphous alloys?
Chalkboard description of substitutional and interstitial alloys and their defects, followed by a demonstration of the hardness of an amorphous (noncrystalline) alloy that has lots of defects.
Why is CO2 a Gas and SiO2 a Solid at Room Temperature?
Chalkboard description of the structure of a carbon dioxide molecule and a tiny portion of the silicon dioxide network covalent structure, with real examples of both compounds. (Correction: I said "pi to pi interactions with other atoms"; I should have said "p to p interactions with other atoms".)
Which is the Hardest Carbon Allotrope?
Discussion of fullerenes, graphite, and diamond and their intermolecular forces using molecular models.
Why is Polystyrene More Rigid Than Polyethylene?
Polymer samples (recycling codes 1-7) and chalkboard discussion of why polystyrene is more rigid than polyethylene.
How were the plastic knives formed together?
Demonstration and chalkboard descriptions of solvent swelling and solvent welding using polystyrene butter knives, an orange peel, and acetone.
Why does tin make a noise as it is bent?
Detecting Tin "Cry" Using a Vernier Sound Sensor
Make sure your sound is on. Bending heavy copper wire and then a tin rod next to a Vernier sound sensor. The bending copper metal does not make noise as dislocations move through its structure, but when tin is bent, the phenomenon called dislocation twinning causes it to make a crackling noise.
How could you explain crystal growth and defects using this demonstration?
A BB board is used to illustrate aspects of metal structures at the atomic level, including crystal growth and defects.
How would you describe elastic and plastic deformation after watching this video?
Mechanical properties of metals such as elastic and plastic deformation and work-hardening illustrated by bending a paper clip.
What’s happening to Abe Lincoln’s nose?
Visitors to Abraham Lincoln's tomb in Springfield, IL, often rub the nose of the bronze sculpture of Lincoln's head. The rubbing has exposed crystallites and grain boundaries in the bronze. CORRECTION: I said "brass" in the video. I should have said "BRONZE".
What does adding azobenzene to eicosane do to the melting point of the substance?
Adding a little bit of azobenzene to eicosane lowers its melting point to where it can be melted by the heat of a gloved hand more readily than pure eicosane or pure azobenzene. Freezing point depression can occur in water (salt water freezes at a lower temperature than pure water) and is also cited as a reason why liquid water might possibly exist in certain conditions on Mars.
How does this video demonstrate the thermodynamics of crystallization?
Plastic spheres (ABS airsoft ammo) spontaneously assemble on the surface of 20% NaCl solution. The assembled spheres can be solvent welded together with a little ethyl acetate. Cut lengths of soda straw also assemble well on the surface of water. These macroscopic assemblies are good demonstrations of the thermodynamics of crystallization.
Campbell, D. J.; Freidinger, E. R.; Hastings, J. M.; Querns, M. K. "Spontaneous Assembly of Soda Straws." J. Chem. Educ., 2002, 79, 201-202.
Campbell, D. J.; Freidinger, E. R.; Hastings, J. M.; Querns, M. K. "Spontaneous Assembly of LEGO®s." Chem13 News, September 2001, 8-9.
How does the sound change as the temperature of the cup is changed?
A room temperature polypropylene cup moved outside and dropped on concrete repeatedly at about -20 C. As the cup cools down through its glass transition temperature, it becomes more rigid and brittle and makes a higher pitched noise. Compare the noise the cup makes at the beginning and end of the video. When the cup is moved back to warmer temperatures the sound shifts back to a lower pitch.
How does temperature affect the glass transition of the cup?
The pattern is not perfect, but polypropylene cups tend to be more flexible and less likely to crack after being at +17 C indoors and more brittle and more likely to crack outside at -17 C (below their glass transition temperature). Now that's what we call a cold snap!
How are isotactic, syndiotactic, and atactic polystyrene illustrated?
Using a model (made from scrap polystyrene components) to illustrate isotactic, syndiotactic, and atactic polystyrene.
How does change in pressure affect the plastic bottle?
Five years ago I opened this plastic bottle at the summit of Pikes Peak, CO, (altitude ~4300 m) where the pressure is about 0.6 atm. When the bottle was brought down to Peoria, IL, (altitude ~150 m) where the pressure is about 1 atm, the bottle contracted and has stayed that way. When the bottle is placed in a vacuum dessicator and some of the air is removed, the bottle expands again. When air is let back into the dessicator, the bottle contracts again.
What causes the flashes in the rocks?
Two pieces of quartzite are struck together with glancing blows. When this happens, some of the quartz crystals in the rocks are squeezed, and the shifting of chemical bonds and dipoles cause electrical charges to build up. These discharge within the rocks to create brief flashes best viewed in a dark room. This conversion of mechanical stress to electrical charge is known as piezoelectricity. CAUTION: Wear eye protection. Sometimes when rocks are struck together, pieces fly off.
How does the liquid nitrogen affect the packing peanut?
Crushing a Starch Packing Peanut Soaked in Liquid Nitrogen
Crushing a starch packing peanut with a wooden block at room temperature squishes it more flat without much fanfare. Stepping on a starch packing peanut soaked in liquid nitrogen for about ten seconds with a wooden block or a shoe makes an interesting hissing/splatting/crushing noise as the starch structure breaks into small pieces and the liquid nitrogen is released.
Why does the packing peanut shrink when placed in liquid nitrogen?
Polystyrene Packing Peanut Shrinks Reversibly in Liquid Nitrogen
A polystyrene packing peanut shrinks when soaked in liquid nitrogen. The gas pockets shrink when cooled (Charles’s law). When the foam is warmed to room temperature, the peanut returns to its original size. The packing peanut does not really seem to become more rigid at cold temperatures, perhaps because the polystyrene is already in its glassy state.
Siphoning Bead Strand
Attempting siphoning strands of connected beads (also known as the chain fountain or Mould effect). I saw Gary Trammell from the University of Illinois-Springfield use this to illustrate long polymer chains. As this clip shows, you do not want to tip the container too far.
How are the octahedral and tetrahedral holes demonstrated with this fruit?
Modeling Octahedral and Tetrahedral Holes with Fruit
In these tasty models of octahedral and tetrahedral holes, anions are represented by Mandarin oranges and cations are represented by a grape and a blueberry.
How can you use a 3D model of a unit cell to determine the stoichiometry of a molecule?
NaCl Unit Cell Stoichiometry
A model showing the true unit cell boundaries for sodium chloride (blue spheres = sodium cations; white spheres = chloride anions) is unpacked into layers. The fractions of ions within the unit cell associated with each layer (z=0, 1/2, and 1) are added up to obtain the 1:1 ratio of sodium ions to chloride ions.
About how much of the tetrahedral holes do the zinc ions occupy?
Zinc Sulfide Crystal Model Comparison
Comparison of the arrangement of zinc ions (gray or white spheres) and sulfide ions (yellow spheres) in sphalerite (zinc blende) and wurtzite. Sphalerite has a cubic closest packed arrangement of sulfide ions and wurtzite has a hexagonal closest packed arrangement of sulfide ions. In both cases, the zinc ions can be thought of as occupying half of the tetrahedral holes in the sulfide ion lattice. Fun fact: If both the zinc ions and the sulfide ions were somehow changed to carbon atoms all tetrahedrally bonded together, the cubic sphalerite structure would become the diamond structure and the hexagonal wurtzite structure would become the mineral lonsdaleite.
How do the structures of different carbon materials differ?
Carbon Structure Models
Comparison of models of diamond, graphite (and graphene), a carbon nanotube (with a (3,3) configuration), and a buckminsterfullerene (C60). Samples of the real carbon structures are also shown.
How do the atomic arrangements change when at different corresponding planes?
LEGO brick models of face-centered cubic structures, showing atomic arrangements along planes corresponding to (100), (110), and (111) Miller indices.
How are exploding glass drops developed in the 17th century related to cell phone screens?
Prince Ruperts Drops and Gorilla Glass
Prince Rupert’s drops were used as party favors and practical jokes back in the 17th century. The drops are formed as molten glass cools quickly. As the drop cools, the exterior surface hardens first. As the glass on the inside cools and hardens more slowly, it gradually contracts so that the resulting drop has large compressive stress on the exterior surface and tension in the interior. Glass under compression prevents small cracks from widening, so the heads of the drops are very strong. Cracks spread very quickly in glass under tension, so breaking the tail off the drop can cause the glass to fly apart. For Gorilla Glass, used in some cell phones, the surface of the glass is strengthened by placing it under compression by exchanging sodium ions in the glass with larger potassium ions.
(CAUTION: This demonstration involves melted glass and flying bits of sharp solid glass. Use protective measures.)
Special thanks to Audrey Stoewer for scripting, narrating, and filming this video.
Why does one ball bounce while the other doesn't, even though they look identical?
Happy & Sad Balls
Description: Two similar balls are compared to test how their structures relate to their properties. The "happy" ball is made of polychloroprene and the "sad" ball is made of polynorbornene. See what happens when both balls are dropped from the same height!
Special thanks to Audrey Stoewer for making this video.
What do the cold temperatures do to the golf ball? Why?
A golf ball that has been physically altered breaks open in liquid nitrogen, breaking the glass beaker in which it was placed. This seems to be due to the cold temperatures both hardening and creating stress in the interior of the ball.
WARNING: This energetic process is dangerous. Do not attempt.
Liquid nitrogen cooled racquetball dropped into plastic bottle shield
Racquetballs dropped into shield made from large water bottle at room temperature (where it bounces) and when cooled below the glass transition temperature with liquid nitrogen (where it breaks).