Thirteen (mostly) Chemistry Demonstrations in 280 Characters Or Less

  1. Ground #helium balloons with a bunch of grapes. Then remove 1 grape at a time until the buoyant & gravitational forces balance out. The balloons will be suspended in the air. Children quickly catch on and have injected a little #science into an otherwise dull wedding reception.
  2. Add copper to HCl & watch nothing happen. Add Cu to HNO3, & NO2 or NO forms, depending on the acid’s concentration. Add CuO to citric acid, wait a few days & a (patina-like?) material forms.
  3. ZNO44To a beaker, add sand and a 50% solution of methanol. Then add spatula tips of zinc oxide powder. Close lights. Transitions are very temperature-dependent and different parts of the flame create a variety of colors. Students prefer demo to drugs.
  4. Add calcium to water & phenolphthalein. Collect H2. Ignite it. Color change in solution reveals hydroxide formation. White precipitate of CaO settles below fuchsia solution. Filter it. Blow into solution of Ca(OH)2 to form CaCO3. More CO2 forms acid, gets rids of cloudiness.
  5. ammoniaAdd 2 drops of bromothymol blue to a (pH ~ 4) solution in a flat-bottomed flask. Add dilute NaOH to beaker. Bring the flask to a boil for 3-5 minutes. Remove heat source & wrap a cold, wet rag around the flask. Be awed by work of ΔPV.
  6. Get a hand-held digital microscope. Use it to reveal  the sensuous surface of a grapefruit, an aborted seed; and the oxidation of copper in an old penny. 

SANYO DIGITAL CAMERAChip off 5 samples from a boulder. Use water displacement in large cylinder to find the volume of each piece. Mass each rock. Obtain average density. With latter & an estimate of the boulder’s volume, get an estimate of the boulder’s mass.
8. Get a thin flow from a water tap. Wrap cotton shirt around a plastic comb. Rub it. Move the comb towards the water without touching it. Watch the stream bend like a banana. Water is neutral, but something charged within it is attracted to the oppositely charged comb.Static 9. Demonstrate that old pieces of magnesium often won’t flash in a Bunsen burner flame. Their surface has reacted with air. Wipe a piece with a paper towel that’s wet with dilute acid. Dry, weigh, ignite& look away! After it flashes, reveal that white residue’s mass > than original.
10. CO2Add two drops of bromothymol blue to 4 different test tubes containing tap water. Add distilled water to the 1st; it remains green. Add baking soda to 2nd, get blue. To the 3rd and 4th add vinegar & dry ice (CO2). Both go yellow as both additives lead to H+.

11. Ignite a hydrogen-filled balloon. Note red color from excess H2 incandescing in heat of reaction. Fill a 2nd balloon with 2:1 ratio of H2 to O2 & ignite; observe no red color. Fill 3rd balloon with hydrogen and add a little copper sulfate. Explosion becomes green-colored.

12. Spread a few grams of iron filings on a filter paper. Place it a magnetic stirrer. Turn it on at medium speed. A beautiful display of a magnetic field in motion ensues. It resembles a living colony of microorganisms.

13. The calcium carbonate in blackboard chalk is long-baked, so it quickly settles, and more stays out of the respiratory system. Yet, if you examine any ledge or border high above the board, it fills with chalk dust over the school year. How? Brownian motion.

14. Imagine someone you has wronged you. Imagine taking a wet sheet of newspaper& sticking it on the guy’s windshield on a cold day. Due to H-bonding he’ll never be able to scrape it off, unless he has access to hot water. Imagine writing on the paper, “Revenge is best served cold.”

More to come.

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The Beautiful Display From Zinc Oxide in Methanol

When zinc oxide (ZnO) is added to burning methanol, we see blue emissions along with sparks and beautiful flashes of red and green. Why? One student had found it so incredulous that they thought our ZnO was contaminated with other substances. It’s unlikely, but you could check the hypothesis by using another source of zinc oxide to compare the results. Years ago, I originally didn’t have the answer to the question, and  it encouraged another student, Veronica Chudzinski,  to untangle the mystery! ZNO4

Of course we were already aware that electrons get promoted to different energy levels by the flame’s heat, and then depending on which level they are falling back from, we get different colors. We were also aware that the blue is from methanol’s emissions. After some research, Veronica learned that through electron-emissions, ZnO can produce two distinctive colours, red and green. But why two levels and an ensuing pair of colors?  The ZnO produces both colours because it is responding to different temperatures within the flame.  To be more precise:

  • ZnO leads to red emissions between 568 to 704 °C degrees Celsius
  • ZnO produces green between 704 to 948 °C

A methanol flame’s maximum temperature is 1152 Kelvin, which is about 880 degrees Celsius so this is consistent with the idea that both colours were produced by the ZnO.

Why the beautiful sparks?

The sparks observed result from ZnO particles that have fallen into the solution; then, as they were lifted with the flame, the methanol evaporated off them and the remaining dust particles produced the linear bursts of light through incandescence.

A word of caution. When using even a 50% solution of methanol in emission demonstrations and experiments, the high temperature of the burning methanol can easily break Pyrex glass. As a crucial precaution, use sand at the bottom of the beaker, which will make the glass more resistant to extreme heat. And do not have students sitting or standing any closer than about 10 to 12 feet from the flame. Equip them with goggles.

Veronica’s Sources:

Bulletin of the National Research Council Volume 5

If temperatures quoted seem high, they are in fact plausible. See: Flame Temperatures

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