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Jul 06 2011

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Cool Chemistry Demo’s

This is a set of cool Chemistry / Physics demos which can be quite exciting and dangerous. They are not mine so I take no resposibility for each one or how you apply it. I have only put them here for reference to give you some ideas!

Methane Bubbles. Methane from a natural gas line or a lecture cylinder is connected via a piece of rubber tubing to a very small funnel. After a slow flow is started, the funnel is put into a petri dish containing bubble solution. This takes practice but it is possible to produce bubbles which when shaken free of the funnel rise into the air. The bubbles are ignited with a Bunsen burner or a barbecue lighter. The same experiment is repeated with air if it is available. The burning bubbles are most dramatic in a darkened room. Be sure to have a fire extinguisher handy when you do this experiment and be careful not to ignite the methane anywhere but at the bubbles.

Liquid Nitrogen.

1. A balloon is attached to a piece of vacuum hose with a hose clamp. The other end of the hose is connected to a plastic bottle containing a small amount of liquid nitrogen.

2. An inflated sealed balloon is slowly pushed into liquid nitrogen. Balloons that have bulges or twists are preferred. After the balloon has shrunk to a minimal size, it is allowed to warm to room temperature. If a helium filled balloon is used and the balloon is released in the liquid nitrogen, it will eventually warm up and float to the ceiling.

3. After liquid nitrogen is added to a plastic bottle, a rubber stopper is securely inserted into the bottle. After several seconds it will shoot out into the audience if aimed properly.

4. Into the plastic bottle containing liquid nitrogen, insert a rubber stopper with a 25 cm long piece of 7 mm tubing that reaches to the bottom of the bottle. A fountain will quickly result and if sufficient nitrogen is used, it is possible to almost disappear in the descending fog. The rubber stopper should be held in carefully as on rare occasions, liquid nitrogen runs down the glass tube and can freeze your hand.

5. A marshmallow is placed on a copper wire and inserted into liquid nitrogen. After about 3 minutes, gentle tapping in a beaker will shatter the marshmallow.

6. Liquid nitrogen can be harmlessly poured quickly on the back of your hand for very short periods of time.

7. Have the children separate if the floor is carpeted and leave a wide aisle and throw some liquid nitrogen onto the floor between them.

Welcome School Sign. A 5% aqueous potassium ferrocyanide solution is used to write “Welcome” and a 5% aqueous potassium thiocyanate is use to write the name of the school. The sign is sprayed using a pump sprayer with a 1% aqueous solution of iron(III) chloride.

Paper chromatography. Felt tip pens are used to spot a piece of Whatman #1 chromatography paper cut appropriately (11 x 19.5 cm) to fit a 600 mL beaker. The paper is suspended with a large paper clip on a pencil. When water is used as the solvent, the separation is not complete but sufficient for students to see separation and differences between different colors and the same color of different brands. About 40 mL of a 1:1:1 mixture of 1-butanol, ethanol and 2 M ammonia works much better with some brands and the mixture seems to be stable for long periods of time. It does require more time for preparation and it smells.

Vacuum Experiments. Plastic bell jars and portable vacuum pumps are available form commercial lab supply companies. The latter are rather expensive and a relatively good one is needed to pop the balloon. Around Easter, it is advisable to stock up on marshmallow chickens and rabbits.

Molecular Motion. A drop food coloring is added to tall 200 maL beakers containing room temperature and very hot water. The heater stirrer unit should be one that heats rapidly and does not have the word magnetic printed on the front.

Endothermic Reaction. Vials containing 20 g of Ba(OH)28H2O and 10 g of NH4SCN (other chemicals can be substituted such as Sr(OH)28H2O and/or NH4Cl but the reaction is not quite as dramatic). The formation of water and frost can be observed and the presence of ammonia detected by smell. The flask gets cold enough (-20oC) to condense moisture form the air. The condensation can be demonstrated by rubbing some of the frost with a finger. Some students near the front can be allowed to touch the flask and tell the other students that it is cold. Some students assume all chemical reactions evolve heat and confuse the frost with steam. The flask gets cold enough to freeze water added to the bottom of the flask and the flask can be frozen to a smooth surface using ice as glue.

Blue Bottle Experiment. The following four solutions are prepared and stored in plastic bottles and dropper bottles.

Solution A: 32 g KOH/500 mL water
Solution B: 40 g dextrose/500 mL water
Solution C: 0.04 g methylene blue/100 mL water
Solution D: 1 g resaurzin (tablet form)/100 mL water

Mix about 30 mL of solution A, 30 mL of solution B, 10 drops of solution C and 10 drops of solution D. Stir, allow to sit and turn pink and then almost colorless (several minutes the first time and shorter amounts of time later depending on the amount of stirring). Pick up the flask very carefully and give it one quick swirl to turn it pink. Continued stirring will turn the solution purple. The cycle can be repeated many times.

Exothermic Reaction. Fill a vial with KMnO4 that has been ground up with a mortar and pestle. Place about a pop bottle cap full in a Pyrex Petri dish and add a few drops of glycerol to the KMnO4. After several seconds, the mixture will start to smoke, crackle and eventually ignite. Unfortunately, the reaction also give off a nasty smell.

Canned Heat. In a Pyrex Petri dish, put a few mL of saturated aqueous calcium acetate solution (about 35g/100 mL). Add ethanol, mix, and pour off the excess alcohol from the gel formed. Ignite with a match and sprinkle some boric acid on the flame.

Clock Reaction. Prepare the following two solutions in plastic bottles:

Solution A: Dissolve 4 g of soluble starch in 1 L of boiling water. After cooling, add 2 g of Na2S2O5.
Solution B: Dissolve 2 g KIO3 in 1 L of water containing 0.3 mL of concentrated sulfuric acid.

Mix: 25 mL of solution A and 25 mL of solution B (about 13 seconds for color change)
Mix: 25 mL of solution A and 50 mL of water and then add 25 mL of solution B (about 55 sec.)
Mix: 25 mL of solution A and 50 mL of very hot water and then add 25 mL of solution B (about 30 seconds)

    To turn this reaction into the Old Nassau (Halloween) reaction, add 10 mL of a mercuric chloride solution
          (0.15 g HgCl2 per 100 mL H2O) to a flask followed by 25 mL each of A and B.  After about 0.5 minutes,
          the solution will turn orange and another 0.5 minutes later, dark purple.  Be aware of the disposal hazards
          of mercury(II) ion.

Oscillating Clock Reaction. Prepare the following solutions in plastic bottles:

Solution A: Dilute 206 mL of 30% H2O2 to 500 mL with water.  [Note:  Walter Rohr informs me that 27%hydrogen peroxide can be purchased under the trade name Baquacil Shock and Oxidizer from pool stores.  Check with http://www.archchemicals.com/Fed/BAQCIL  for location of stores.]
Solution B: Dissolve 21.4 g of KIO3 in 500 mL of water containing 2.2 mL of 18 M H2SO4.
Solution C: Dissolve 3 g of soluble starch in 750 mL of boiling water. To the cooled solution, add 11.7 g of malonic acid and 2.5 g of MnSO4H2O.

Mix: Equal volumes (for small audiences, 25 mL of each is sufficient) of solutions A, B, C in an Erlenmeyer flask. While the demonstration is dramatic in an Erlenmeyer flask, it is even more impressive if the solution is quickly transferred to a graduated cylinder as there is a spatial effect to the oscillations easily observable.

Nylon. In a glass bottle, prepare a 0.25 M adipyl chloride solution in cyclohexane. Transfer about 20 mL of this solution to a plastic dropper bottle. In a plastic bottle, prepare an aqueous solution containing 0.5 M 1,6-diaminohexane and 0.5 M NaOH. Put about 2 mL of the amine solution in a shallow dish or watch glass and while adding the acid chloride solution dropwise, slowly pull out the nylon with a looped copper wire.

Chemilumescence. Prepare the following solutions in plastic bottles:

Solution A: Dissolve 2 g of luminol (aminophthalhydrazide) and 2.5 g of NaOH in 1 L of water.
Solution B: 0.15% H2O2

Mix: 40 mL each of solutions A and B in a graduated cylinder. Sprinkle a few crystals of K3Fe(CN)6 into the cylinder for an interesting effect and then add a larger quantity for maximum light output. For a yellow emission, add after the blue emission is observed, a few drops of a solution of 1 g of fluorescein and 1 g NaOH in 100 mL of water.

Mercury shadowgraph. Fluorescence is demonstrated first using a precoated thin layer chromatography sheet with a fluorescent indicator. A short wave (254 nm) mineral is a convenient portable light source. Next, a shallow plastic bottle of mercury opened and placed between the light and the fluorescent screen. In a sufficiently darkened room, the shadows of the mercury vapor are easily observed on the screen. A little blowing on the mercury sometimes enhances the demonstration.

Fluorescence and Phosphorescence. Fluorescence can be conveniently demonstrated by writing on Whatman No. 1 filter paper with solutions containing 0.02% methanol solutions of Rhodamine B (caution – suspected carcinogen), fluorescein, or acridine orange. For phosphorescence, write on the filter paper with a 5×10-3 M solution of a polynuclear aromatic acid ( e.g., naphthoic acid, naphthalene sulfonic acid) in a 1 M NaOH solution. 2-Naphthol gives both fluorescence and phosphorescence under these conditions. After drying irradiate with the 254 nm line of a mineral light in a dark room.

Electric Pickle. This experiment should be performed in a well ventilated area or for a very short time only. Cut off the female end of an inexpensive cord and split the wires. Solder large sheet metal screws to each of the wires. Support a large dill pickle in some way that won’t require touching (we use a ring stand and a clamp) and insert the sheet metal screws into opposite ends of the pickle. Plug the cord directly into a socket and after several seconds smoke should start coming out of the pickle and shortly thereafter, it should start glowing. At this point, the lights should be turned out but remember to run this for a short period of time and be very careful not to electrocute yourself. Students should definitely be cautioned not to try this one at home. There have been several articles in the Journal of Chemical Education on this reaction in the mid 1990’s.

 

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