As we shift to phenomena based teaching it is important to have phenomena that can inspire quality thinking and discussion. Here are some chemistry demonstrations that have short set up times and can be used for instruction in a variety of topics. If you are not a teacher trained in lab safety, please consult MSDS for chemicals used in these demonstrations before attempting anything.
Take a round flask (with flat bottom) and mark a pumpkin face. To the flask add 8 g of KOH and 10 g of dextrose and enough water to mostly fill the container when sealed with a rubber stopper. Once the dextrose and KOH have dissolved, add a small amount of methylene blue solution. The solution will be blue and should fade to colorless. Now add in 2 drops of red and 2 drops of yellow food coloring to create the orange pumpkin. Fix the rubber stopper securely in place and shake the pumpkin. The turbulence will cause more oxygen to dissolve in the solution and alter the color of the dye back to blue creating a black container that slowly fades back to the orange pumpkin.
2. Firetube
Isopropyl alcohol (propan-2-ol) is added to a glass tube so that it coats the inside of the tube. After sitting for a minute the alcohol is poured out of one end of the tube being careful not to get any on the outside. Then the tube is placed over a candle igniting the vapors in the tube. The tube does get hot so make sure to wear a heat glove. You’ll want the room mostly dark (just enough light to see what you’re doing) and very quiet.
A rabbit fur is used to charge a large piece of foam (pool noodle) or PVC pipe. The charged foam is placed near a ruler that is balanced on an upside down evaporating dish. The charged foam is attracted to the neutral ruler causing it to spin.
This is a great demonstration of polarization as the charge in the neutral ruler is not even distributed and the positive charges of the ruler are closer to the negative charges of the foam than the negative charges on the foam. Thus we experience a net force since the repulsion is smaller than the attraction. This is similar to how dispersion forces happen.
4. Fire tornado
A mesh trash can is placed on a rotating platform. A pyrex bowl is placed in the trashcan with a small amount of fuel. Isopropyl alcohol is recommended for the fuel. Methanol will work best if you are trying to make a colorful fire tornado, but methanol is commonly involved in lab accidents where the methanol container ignites from a distance and causes an explosion and severe burns. Ignite the fuel using a splint and tongs. When the platform rotates the air will be pushed inwards by the mesh trashcan causing a tornado to form. The fuel will eventually run out and the flame will extinguish.
The photoelectric effect kit is a great way to show how different types of light cause different accelerations of electrons and how light and chemicals interact. This can be enhanced by using a UV light and a clear container that has been covered in spray sunscreen. The sunscreen will absorb the UV light preventing excitation of electrons in the glow in the dark strip. While you have your UV light out, it can be a fun activity to check various types of currency to see what patterns are hidden in them.
To further enhance the relationship between light and chemicals, have students throw photons to you (an electron) and move into higher energy states when you absorb the photons. When you return to the ground state, emit the photon. Move to various levels depending on which photon you absorb. The energy levels can even get closer together as you move to higher levels.
Take iodine and put it into a large test tube. Take a smaller test tube and put it part way into the larger test tube with iodine. Wrap tape around the smaller test tube so that it remains in place and a seal exists between the two test tubes. Now put the test tube into a warm water bath. The iodine will begin to sublimate and the vapor will undergo deposition on the smaller test tube forming iodine crystals. This will be enhanced if you put cool water in the smaller test tube.
This is a great demonstration for discussing enthalpy, entropy and Gibb’s free energy.
The superheated steam coil is set up and then flash cotton is used to enhance the demonstration. This is a great demonstration to counter the misconception that steam is visible. As the steam gets hotter, it gets hot enough that it is not able to turn back into small liquid droplets that we see as a cloud.
Test tubes are partially filled with zinc sulfate in one and manganous sulfate in the other. The test tubes are suspended from a string and left until they become very still. A strong Neodymium magnet will cause the manganese salt to shift, but it will not affect the zinc salt. This is because manganese ions are paramagnetic due to having unpaired electrons. The zinc ions have a full 3d shell and thus are diamagnetic.
Here malachite is reduced to copper oxide and then copper using a coke reduction. The malachite is mixed with charcoal in a crucible and heated using a meker burner. A small amount of carbon monoxide is produced so only perform this in a room with proper ventilation. The reaction can be used in learning stoichiometry and is a common historical process.
Burning steel wool is a very good demonstration because the mass increases after burning even though small sparks are emitted from the fire. If you care to scale up the demonstration tie steel wool to a piece of string and swing the lit steel wool around in a circle outside clear of brush or anything that could be damaged.
11. Colorful Salts
Equal concentration solutions of Cu2+, Fe3+ and OH- are prepared. Put a small amount of water and a few drops of phenolphthalein into a test tube. Then add 10 drops of the copper (II) solution. Add 10 drops of hydroxide solution and swirl the test tube. It should be blue. Add 10 more drops and again it should be blue after swirling. At this point there is exactly twice as much hydroxide as copper (II) and the hydroxide is bonded to the copper (II) ions (Cu(OH)2). The 21st drop of hydroxide should cause the mixture to turn pink and stay pink.
This can be repeated with the iron (III) solution and this time it will take 31 drops to change to pink. This is a great demonstration when introducing naming and formula writing.
No comments:
Post a Comment