Last-modified: 22 October 1999
See reader questions & answers on this topic! - Help others by sharing your knowledge
Subject: 15. Chemical Demonstrations 15.1 Are there any good compilations of demonstrations? Yes. Good places to start are the four volume "Chemical Demonstrations" by B.Z.Shakhashiri , the two volume "Chemical Demonstrations - A Sourcebook for teachers" by Summerlin and Ealy , or "Chemical Magic" by Ford and Grundmeier [2a]. The Journal of Chemical Education is also an excellent on-going source of novel demonstrations and developments of traditional demonstrations. 15.2 What are good outdoor demonstrations for under 12s? 15.3 What are good outdoor demonstrations for over 12s? 15.4 What are good indoor demonstrations for under 12s? 15.5 What are good indoor demonstrations for over 12s? While waiting for a promised contribution, here is my only contribution, and some from my sci.chem archives. Unfortunately, enthusiastic editing by others allows some of the culprits to go uncredited :-). The ability of water-miscible solvents to mask the hydrophobic nature of Goretex can be demonstrated. Goretex is just a porous PTFE, the same material as PTFE filters - such as Millipore HF. You can easily filter liquid water through porous PTFE, provided the filter is previously wetted with a water-miscible solvent ( usually ethanol ). If a filter is set up on a vacuum flask, ensure the filter is completely wetted with ethanol, turn on the vacuum, and immediately add water - it rapidly filters through. Once it has stopped, it only takes about 15 seconds for the air to dry the filter, then ask a student to filter more water from the same flask. No chance. Pour off the water, surreptitiously add a few mls of ethanol, immediately followed by the same water - and watch it filter through again :-). This is the nearest equivalent our laboratory has to the workshop practice of sending an apprentice out to purchase a spark plug for a diesel engine. It does relate slightly to the real world - indicating why "breathing" fabrics like Goretex should not be used with solvents. From: email@example.com (David Bromage) Date: Tue, 14 Sep 1993 Subj: Re: Need: A safe chemical display The so-called "Blue Bottle Reaction" might be useful. Half fill a 1 litre flask with water and add 10g of NaOH, then add 10g of glucose and up to 1ml of 1% methylene blue. Stopper the flask and swirl gently to dissolve the contents. On standing for a few minutes the solution should turn colourless. When the flask is shaken the solution will turn blue then decolorise on standing. Methylene blue exists in solution as a reduced colourless form and an oxidised blur form. The initially blue dye is reduced by the alkaline form of glucose and re-oxidised by dissolved oxygen. When the solution is shaken, atmospheric oxygen enters into solution at a more rapid rate than when left standing. The dye acts here as a catalyst whose colour indicates the redox state. [ This demonstration, and different coloured versions of it, have recently been discussed in the J.Chem.Ed.. ] How about a chemical garden? Make up (or dilute a commercial preparation) of sodium silicate to 1.1g/ml. Place this solution in a large glass container then add 'lumps' or large crystals of salts to be grown. Lumps should not be more than 0.5cm in diameter. As a salt dissolves it forms an insoluble silicate which forms a membrane around the lump of salt. The membrane is permeable to water which enters and dissolves more salt. The resulting pressure bursts the membrane releasing more salt solution to form more membrane. As the salt solution is less dense than the silicate solution, the membrane grows as a convoluted vertical tube. Salt Colour Growth time Ferric chloride brown 1 hour Ferrous sulphate grey-green 3 hours Cobalt chloride purple 5 hours Chromium chloride grey-green 6 hours Nickel sulphate yellow-green ~24 hours Cupric sulphate blue ~24 hours Potassium aluminium sulphate white ~1 day To produce a "garden" which is not completely overgrown with the faster species it is necessary to take growth rates into account. Distilled water should be used as Ca and Fe in tap water can cause cloudiness. If you really want oscillating reactions, I know of two. A. Iodate reaction. Make up 3 solutions 1) Dilute 200ml of 100 vol hydrogen peroxide to 500ml 2) dissolve 21g of potassium iodate (KIO3) and 1.5ml of conc sulphuric acid in 500ml of water. 3) Dissolve 7.8g of malonic acid and 1.4g of manganese sulphate in 400ml of water and add 1.5g of starch in 100ml of water. Add equal volumes (50-100ml) of each solution to a flask in any order. Colourless-blue oscillations should start within 2 minutes. If not, try 10-20% variations in relative volumes. (try increasing 2 first). Oscillations should last up to 10 minutes but I my experience have lasted up to 3 hours. B. The Belusov reaction Prepare 5 solutions. 1) 58g of malonic acid on 500ml of water 2) 6M sulphuric acid 3) 21g of potassium bromate (KBrO3) in 500ml of water 4) Dilute 5ml of solution 2 to 500ml then add 1.75g of cerous sulphate. 5) 1.6g of 1,10-phenanthroline and 0.7g of ferrous sulphate in 100ml of water (or commercial ferroin solution to 0.025M) Mix together 50ml of 1 to 4 and 5ml of solution 5. Blue-pink oscillations should start within a few minutes. For either oscillating reaction the choice exists of complete mixing with uniform oscillations or waves of colour (eg in a measuring cylinder). Some interchange of reagents is possible. The Bray reaction omits malonic acid from the Iodate reaction. Malonic acid can be replaced by citric or succinic acids. [ There have been several good discussions [4,5], and recipe compilations , for many popular oscillating chemical reactions.] A particularly dramatic 'trick' is not to burn paper. Make up a solution containing 57% v/v ethanol and 43% v/v water with 5% w/w sodium chloride. Soak a filter circle in the solution and hold it near a flame (with tongs) just long enough to ignite. After the flames die down the filter circle will still be intact. The ethanol burns but just enough water remains in the paper to prevent ignition. NaCl is added to provide a more convincing flame. To add drama, 'burn' a banknote - but ensure that all of the note, especially the corners, is soaked. From: firstname.lastname@example.org (Lonnie C Martin) Date: 17 Feb 1993 Subj: Re: Growing a Silver Tree in Beaker? In article <...> email@example.com (kenneth k konvicka) writes: >Am trying to do a demo for elementary school kids. How do you grow a tree >of silver using copper wire(?) submerged in a solution of AgNO3? Saw one >in high school physics class about a thousand years ago at good ol' Reagan >HS, Austin, Tx. Was really beautiful. The silver formed nice large >plates. Any demonstration books you could steer me toward? What you have described is about all there is to it. I do this demonstration for the chemistry classes here at Berkeley about twice a year, or so. Just make a "tree" out of copper wire (you might clean it with sandpaper or steel wool) so that it will fit into a beaker of your choice (we use 4 litre here), and pour in the silver nitrate solution. I think we use 0.1 molar, but as long as the concentration is fairly close to that, it will work just fine. It is not necessary to make the tree very "bushy". The silver will fill it out nicely with fuzzy thick hanging globs of crystals. The solution will change from colourless to blue, as copper nitrate is formed. A very nice experiment. You can expect this to take on the order of an hour to get fully developed. From: firstname.lastname@example.org (Neil Flatter) Date: Tue, 14 Sep 1993 Subj: Re: Need: A safe chemical display We use cobalt (II) chloride in a saturated sodium chloride solution to demonstrate cooling coils. It changes from red/pink to a blue/purple when heated and reverses as it is cooled. We cycle it through a condenser from a distillation to illustrate that portion of a simple set-up. Subject: Stupid lab tricks -Compiled- VERY LONG Date: 7 Jul 92 From: Nazman <email@example.com> Ever try taking an empty ditto fluid can, put some water in it, heat it until steam is coming out, cap it back up and let it cool off?. You would be surprised what a little air pressure can do. That one amazed me when I was young. I was amazed again when I saw a brief description on TV of how science teachers are trying to make science fun again. Four teachers on stage, set up a few ring stands and a few bunsen burners, and placed a 55 gallon oil drum on top. Boiled the water, capped it. Put a hell of a dent in the drum when it collapsed. A favourite of mine requires a little preparation, but is great fun. Try tearing an aluminum can in half. Kinda difficult. Now, if you take an empty can, gently score around the circumference on the inside, (the inside is coated to prevent a reaction between the soda and the can) and fill the can with a solution of warm water and Copper(II)Chloride (CuCl2) so that the solution is just above the score mark. Let this sit for a few minutes. You are done with the solution when the outside of the can appears brownish (blackish) where the score mark is. Gently pour out the solution (keep it) and let the can sit. When ready, hold the top of the can in one hand and the bottom in the other, and break like you are breaking a stick in half. Two bits of advice : BE CAREFUL!. You will end up with the sharp edge of the can, which can cut severely! Try this ahead of time just to make sure you get it right. Wait too long, and when you pick up the can, it will split due to the weight of the solution. Don't wait long enough and it won't work. My guess is about 5 minutes P.S. This is more of a demonstration of structure of an aluminum can, but if you want to demonstrate the "strength" before you rip it in half, place the can on the floor, so it is sitting like it normally would, and balance on one foot off the top of the can. It helps to have something nearby to hold on to, and the can cannot have any dents. You would be surprised how strong an empty can is. I weigh about 190 lbs, and have stood on an empty soda can for 30 seconds, get off the can, and not have it collapse. This takes some practice, so give it a try. From: A_ROSATI@GUVAX.GEORGETOWN.EDU <Anthony V. Rosati> You can followup the bromophenol blue trick by brewing a cup of tea and, while they watch, add some lemon juice. The color will lighten. There is an indicator in tea that changes with the acidity of ascorbic acid. Another neat trick is to demonstrate the dehydration capacity of concentrated sulfuric acid. Take a 500 mL beaker about one third full of white table-sugar. Then add about a half-inch to one inches worth of concentrated sulfuric acid. (This demonstration _MUST_ be conducted in a hood) Let it sit for about five minutes. Within that time, the sulfuric acid will seep in, start turning the color of the sugar brown, and then black, followed by an intense, hot dehydration. The sugar will start to form a jet black, smelly, sticky column that rises out of the beaker. It is really impressive..... You might want to also look up "oscillating reactions" in your chemistry library. Many of these are simple to set up and generate neat color cycles that would impress the kids! From: firstname.lastname@example.org < Lyn Francisco > 1. Take a balloon, blow it up, tie it, then stick it in a vat of liquid nitrogen. Wait until it shrinks (around 3 s or so), take it out, and then watch it inflate in your hands. This will very nicely illustrate the relation between temperature and pressure. 2. We did this during a demonstration to let the world know about ACS on campus. Take a large container (like one of those 10-gallon water containers, cut in half or something), fill it up with water, then put in one can of the original Coke and one can of diet Coke. Make sure that both cans are unopened. Now, drop a few pieces of dry ice in the container. The original Coke should drop to the bottom, and the diet Coke stay up toward the top. It was cool, and attracted all the frat-types and non-science people to our table. From: email@example.com < Dan Field > If you really want to fire them up, my favorite has always been the hydrogen balloons. Just fill up several balloons, one color with air or He, another with H2, and another with 2H2 + O2. You can fill them ahead of time, or better yet if demonstration time allows, use the products of one of your demonstration reactions to fill the balloons. Light a candle on a L O N G stick, dim the lights, and pop!, boom!, B O O O M !!. You'll have instantly created little monsters, young pyromaniacs virtually guaranteed to associate some excitement with chemistry. [ Warning - the sound level of such explosions has recently been found to exceed health and safety guidelines, and people should read the article before demonstrating this experiment to students or children . ] From: edremy@d31ha0.Stanford.edu < Eric R.> There are lots of things you can do with liquid N2. Try freezing a banana and using it as a hammer. (Follow by using an unfrozen banana: kids love it!) Simply adding some to a test tube and (lightly!) corking it is fun, provided you're careful with the cork. Shattering a superball is also good. However, my personal favorite for spectacular demos is the HCl fountain. Ascii graphics follow --------- \ / Top flask is filled with HCl gas \ S S=rubber stopper w/ hole for needle \ / -|- / | \ Run tube from top into bottom /--|--\ Bottom flask filled with water and / | \ acid/base indicator. ----------- MAKE SURE THAT THESE FLASKS ARE VACUUM SAFE!!! To start this whole extravaganza, inject 20-30 cc of water into the top flask. The HCl gas goes into solution, creating a partial vacuum, sucking the water up from the bottom. As the water spurts out of the tube, it collects more HCl (And changes color as it becomes acid) and accelerates the reaction... Quite impressive. We used to do this for our chemistry magic show every year. The only problem is that the failure mode is somewhat dangerous: One year the top flask had a flaw and imploded, sending glass and HCl everywhere. Best to do behind a shield From: Bill I believe that the same thing can be done with ammonia. The same precautions apply. From: ? Bubble H2 through a soap solution and you get bubbles that float up. Have them float through a bunsen burner flame suspended over the table and they explode. VERY NEAT effect. From: firstname.lastname@example.org <Joe> USUAL WARNINGS: many chemicals are poisonous and some reactions may be difficult to control. Use your head. Best done indoors ----------------- Dissolve silver nitrate in warm water. Get some copper wire and clean it with steel wool. Insert copper wire (preferably coiled at one end) in the solution and it will immediately dull. Some time later, silver crystals will be CLEARLY visibly growing on the copper. The best effect is to let it sit overnight. The resulting effect is downright beautiful Dissolve Cobalt Chloride in warm water. Put some Aluminum foil in it and watch it tarnish. Clean, polished Aluminum works best but household aluminum foil also works (just slower). The Aluminum slowly disappears and Cobalt metal shows up at the bottom. This is a slow one but it does work. Light an alcohol lamp, i.e. denatured alcohol and bring a magnet near the flame but not above it- to the side. Watch the flame get pulled in the direction of the magnet. Sprinkle iron filings over the same alcohol lamp and watch sparks fly! Ignite some Magnesium ribbon and drop into an atmosphere of CO2. It will continue to burn with lots of noise and sparks. Carbon dust will rain down as a byproduct. Mix water and household (3 in 1) oil. Note the phase boundary. Add soap and shake. Watch the phase boundary disappear. Heat up a piece of blackboard chalk with a propane torch. Chalk is CaCO3 - heating it up will drive off CO2, leaving CaO (also known as lime). Heating up lime will cause the it to emit a whitish light, which is where the phrase 'limelight' comes from. [ Note - not all blackboard chalk is CaCO3 - test carefully first ] Do these outdoors: ------------------ Get some KMnO4 and pour into a small pile. Depress the center of the pile slightly and add a drop or two of Glycerine and stand back. Something between 1-5 minutes later, it will burst into flame. When it dies down, drop some more glycerine on it to have it flare up again. Be careful disposing of the KMnO4 left over - its a powerful oxidizer. We also do THERMITE periodically (Aluminum powder and rust). Details for those who ask - it burns *BRIGHT* and *HOT*. Drop some dry ice chunks into a 2 liter PLASTIC soda bottle 1/2 full with warm water which is then quickly sealed. Get at least 50' ft back rather quickly. The pressure will build up and detonate with a LOUD *BOOM* after a brief and unpredictable time. The bottle will break into many hundreds of parts (don't use GLASS!) and you will get a mist cloud some 20-30' across. Note: It is quite LOUD and may scare a younger audience. Make Hydrogen soap bubbles and set them off. Get an erlenmeyer flask and fit a cork into the top and route a glass tube through the tube and have it bend down and into a jay of soapy water. Remove the cork and drop in Zinc metal and pour in somewhat dilute HCl. Put the cork back in and let the H2 bubble into the soapy water. This will make H2 soap bubbles. Let them break free and ignite them with a light match on long pole. Thermite reaction First of all....this is a fairly vigorous reaction so take the usual precautions: 1-Do it outside, preferably on sand or dirt. Since it burns at 4000 degrees fahrenheit, it will melt most anything. By the way, a nuclear explosion burns at 8000 and the surface of our Sun burns at 10000. It will readily melt rock salt, beach sand, etc. You get the idea. 2-It can spray sparks around. Keep it away from combustible materials. The burning sparks are either molten Aluminum or molten Iron. 3-It is VERY bright so you shouldn't stare at it. 4-It puts out lots of smoke. Here is how I do it. Ingredients: 1-Aluminum powder 2-Iron Rust (Red-Fe2O3). Grind carefully and separately into a powder-like consistency. Mix in roughly equal proportions, by volume with an excess of rust. Mix thoroughly to get an even color. Pour the powder mixture on the ground in a pile. Get magnesium ribbon and lay it on top of the pile, and press partially into the pile. Do not smother the Mg ribbon. Ignite the ribbon with a propane torch and get back quickly. When done, be careful...it will leave molten, glowing red iron as a byproduct. You can make rust by mixing household clorox with steel wool pads and let sit overnight and then filtering out the rust. Have fun and be careful. Usual disclaimers apply From: email@example.com < Justin Gallivan > This works nicely with soap bubbles in a dish. If you have the H2 and O2 tanks available, Try a few with the H2 only which makes a nice quiet flame and add the O2 later for a little shock value. You may want to try this first for safety's sake but it always went off without a hitch in my general chemistry days. From: Rob I hope I'm not too late. An extremely simple trick is done with a chunk of styrofoam (larger the better) and some acetone, which is an excellent theta-solvent for styrofoam. Simply spray the acetone out of a bottle onto the styrofoam, and the styrofoam rapidly decomposes, losing its structure, and appears to actually be melting. It is quite a "dramatic" demonstration, and can be offset against how nicely styrofoam coffee cups hold water/coffee, but not acetone. From: ? I thought this one was neat... Take a bottle (should be reasonable size, like a ketchup bottle) fill it to within 2" of the top, color light blue (not opaque!) with methylene blue. Drop in a NaOH pellet and a few drops of Karo clear syrup. Other reducing sugars might work; I just know it works with this syrup. (Or did; the last time I tried it was almost 20 years ago, and they may have changed the formula since then.) Over a period of a few minutes, the blue color will fade. Shake the bottle, and suddenly it's blue again. Leave it, and it will slowly fade. It'll last for a couple of days, until random microbes do in the sugar I suppose. From: ? A "Bottle of fire" for lighting bunsen burners and such: Get a dark, heat-resistant glass bottle, and put just enough pentane in it to wet the sides. (i.e., rinse it with pentane and dump out the excess.) Light the top of the bottle. The flame will burn down into the neck of the bottle a little, but be almost invisible to the audience. Pick up the bottle, turn it over, and flames will pour out. Set it down, and the flames seem to go out. When Dr. Toffel did this, someone said "There's something in the bottle!" He said "Nope," poured some water from the faucet into the bottle, dumped fire and water into the sink, then showed that the bottle would still "pour fire". (This probably takes some practice.) From: firstname.lastname@example.org < Mike Van Pelt > Portable bunsen burner: Bubble air through a test tube of pentane, and run this to your bunsen burner. You can use a large balloon as your air source, or have a vict... I mean, volunteer, blow through the tube. From: Howard Clase. One experiment that I like was you make a solution of lead nitrate, which is clear, and a solution of some iodide salt (potassium iodide), which is also clear. When you mix the two of them together you form a yellow solid - lead iodide. This is only half of it! If you don't use too much of the chemicals to produce your "instant orange juice" - but DON'T let anyone drink it. You will find that the lead iodide will dissolve if you heat the solution. On Cooling it re-precipitates as beautiful golden spangles. From: email@example.com < Matthew Gray > Another exciting and easy impress all trick is to get two solutions, one of Ag(I) and another of Cu(I), usually both hexamine complexes. When these two are mixed, a redox reaction takes place, producing a silver mirror effect. Other reducing metals can be used, such as iron, but I haven't tried these myself. From: ? Grind some potassium permanganate to a fine powder (to speed up the reaction). Put it in a small heap (1 teaspoon) on a tile, make a dent in the top and pour one drop of glycerine in the hole. After about 10-15 seconds the heap will catch fire. From: firstname.lastname@example.org Here are some that are rather interesting. All of these tests have been performed in my workshop and are all safe (with the exception of the handling of HCl and the irritating effect of experiment #2). Experiment #3 is by far the most fascinating. 1 Copper Sulfate couple grams in a test tube. Sodium Bicarbonate - same as above. These two liquids are transparent but when mixed, turn into a soft blue opaque suspension. 2 Glycerin and HCl Takes a long time (couple of hours) to complete but when these two clear liquids are mixed together, it turns from clear to a deep transparent red and slowly goes brown. Warning - this is extremely irritating to the eyes if you are exposed to it for a while - usually, an hour is enough to really get you annoyed. 3 (My favorite) Acetone (you can buy large tins of this stuff (1L) at a hardware store in the automotive section (usually with the bondo and other body repair supplies) and styrofoam (a large bag of popcorn type packaging filler will be needed.) When styrofoam is placed in acetone, the styrofoam ( large volume of styrofoam for a small volume of acetone ) dissolves and becomes a wet, play-dough like substance that feels cold to the touch. This experiment is harmless unless swallowed :-) and should prove to be quite interesting to the students. The coldness is due to the evaporation of the acetone from your skin (ever use nail polish remover? That's acetone.) The acetone will eventually all evaporate (a 2 inch sphere of this will take a day or two) and the result will be a porous (trapped acetone bubbles) material that can be molded to any shape you wish. From; David O'Driscoll. University of Central Queensland... Hope someone hasn't already done this one, I have been studying for exams so have not been reading all of them. The one we use at our high school demos are pH clocks.... quite good as they are not static displays. First, take three or four large (1L) beakers and 3/4 fill them then take your favourite pH indicators (ones with good colours), and add a few drops to them, then add some dilute sodium hydroxide or something to make them slightly basic. Next add a handful of dry ice to each beaker. This creates a nice bubbling mixture with good visual effects, what happens is obvious (I hope!!!). Some of the CO2 is dissolved in the water, turning the mixture acidic and when the end-point of the indicator is reached the colour changes - sometimes quite dramatically. The kids seem to like it and the chemistry is not too involved. From:webbb@mbf.UUCP ( Bryan Webb ) I didn't see the originating message of this thread, but from the responses that have made it here, I think this is the kind of stuff you might be looking for. In earlier times, I've done these: 1) Place a small pile (several grams) of powdered magnesium on a surface you don't care about in an environment provided with plenty of ventilation. On top of this, place a couple of grams of powdered iodine (well, as close as you can get to it, though that might not be crucial). Now, put a couple drops of water on the iodine ... enough to also contact the magnesium ... and stand back. The heat of the reaction vaporizes some of the remaining iodine into a purple vapor. 2) This is pretty dangerous, so be very careful. Take a couple of grams of red phosphorous and place on top of a couple of grams of potassium iodate. Rapidly stand back... spontaneous combustion. My experience was a time delay of a couple of seconds, but I wouldn't want to count on it... I discovered this accidentally... boy was I surprised. The speed of the reaction may be related to the humidity. 3) Potassium dichromate is normally bright orange at room temperatures. If it is cooled to liquid nitrogen temperatures, it becomes yellow. If heated, it becomes a deeper red color. I'm not aware of any other inorganics that have this range of color change when the temperature is varied. 4) Ahhh, my favorite... When I was in high school, I took the 2nd year chemistry class that was offered. We had the resources of the school at our disposal, so long as the experiment we wanted to do was "in a book". The book I had was "Chemistry Magic", and described an "experiment" where some cotton balls were placed on a fireproof surface, a few grams of Sodium Peroxide was placed on top, and then you put a drop or two of water that will wet at least a little bit of both the peroxide and the cotton. It's a long story, but I this experiment worked, at least on other cellulose objects like paper towels. In fact, the fire in the metal trash basket was hot enough to melt/burn away the bottom, the linoleum underneath, and some of the concrete in the floor. The flames formed a "solid" yellow flame and lots of thick white smoke (containing NaOH dust). You really don't want to breathe this stuff. We didn't, anyway :-) 5) Oh, another thing we did in that class was take the gas outlet used for the bunsen burners and direct it into a test tube that was partially submerged in liquid nitrogen. (The whole system was sealed.) The gas condenses into a liquid... the only problem was safe disposal. It helps to plan ahead! :-) [ Note that email@example.com subsequently supplied the following warning ] " If you decide to try this be aware that liquid nitrogen will condense liquid oxygen in a vessel open to the air immersed in it. Liquid O2 forms explosive mixtures with many organics. IF you still want to try it, immerse the tube in the nitrogen and then immediately run the gas in. only do a little bit. How much you get depends on what proportion of weights of low hydrocarbons the gas contains ( I think methane condenses at this temp, but not quantitatively like some stuff, unless there is a large surface area)." 6) One of my classmates made luciferin [sic]. It's a liquid that glows in the dark for about 12 hours. That was fun too! Happy researching! Standard disclaimers apply; I'm not sure my company would have hired me if they had the foregoing admissions before them. Non-standard disclaimers too: I don't recommend you do any of these things either. From: firstname.lastname@example.org < fred > If you would like to condense out methane gas in a relatively safe way, fill a balloon with the gas and THEN condense the gas with liquid N2. You can use scissors to cut the balloon, and pour the liquid CH4 into a beaker with water in it (notice that it floats, forms ice, etc.) and light it. Only the fumes burn as they mix with atmospheric oxygen. This makes a fair "olympic torch." Wear goggles etc. From: Larry (Call me "Lefty") C One that can be safely performed with a long enough spatula. Mix Calcium Carbide with any strong oxidizer (KMnO4, NaNO3, even MnO2 works). Proportions aren't real important here. Using face shield, gloves, lab coat and long spatula, drop a SMALL amount (say, 1 gram or so) of this into common household bleach. Acetylene and chlorine are evolved, which immediately, uh... exploded Delightful chlorinated hydrocarbons result, unfortunately :( 15.6 How do I safely perform the Glowing Pickle experiment? This experiment consists of electrically heating a vegetable that has been soaked in a brine solution to conduct electricity. Because this experiment involves electricity at dangerous voltages, the experiment should be performed on special apparatus under qualified supervision. I'm not going to detail the equipment and procedures, as they have been described in an Journal of Chemical Education article . The experiment has not just been limited to table salt and pickles, many other vegetables and salts that produce different colours have been investigated and described in the same issue of the Journal of Chemical Education . People intending to perform the experiment should obtain both articles. 15.7 How do I make Slime?. " Slime " is a trademarked commodity obtained by cross-linking guar gum and borax, and is marketed by the Mattel Toy Corporation. The slime produced for demonstrations is usually made by cross-linking a poly vinyl alcohol (PVA) product using borate. The normal method is to carefully prepare a 4% mass/volume aqueous solution of a hydrolysed high molecular weight PVA ( >100,000 ) - available from Eastman Kodak. Commercial PVA-based adhesives ( such as Elmer's Glue ) will also produce a reasonable quality slime, as will polymeric materials that have multiple hydroxyl groups and can form highly-hydrated gels, such as guar gum - but some experimentation may be required to ascertain optimum ratios. High MW polymers are difficult to dissolve in solvents ( including water ), and the best method is to carefully sprinkle the powder over a beaker of water that is being gently stirred, and continue gentle stirring until a uniform solution with no gelatinous lumps is obtained. Any grade of borax ( Na2B4O7.10H2O ) can be used to prepare a 4% mass/mass aqueous solution. The slime is made by vigorously mixing the two solutions in the ratio of 1-2 parts of the borax solution to 10 parts of the PVA solution using a paddle stirrer. Details of a suitable procedure for use in classrooms have been published . A firmer, less messy, slime can be prepared from an 8% PVA solution - using equal ratios of the 4% borax solution . The properties of slime indicate that the cross-linking mechanism does not consist of strong covalent bonds. Borax hydrolyses in water to form a boric acid-borate buffer with an approximate pH of 9. B(OH)3 + 2H2O <==> (B(OH)4)- + H3O+ pK = 9.2 The borate ion is tetrafunctional when interacting with the alcohol groups of polyols, and thus builds the cross-linking structure. PVA has about 1-2% of 1,2 diols amongst the remaining 98-99% of 1,3 diols. To obtain the desired properties, the bonds between the borate and the PVA must be weak, and it is believed they are hydrogen bonds ( shown as ... below ). PVA Borate PVA H H | | O-H...O O-H...O \ / \ / \ / H-C \ / C-H / B- \ CH2 / \ CH2 \ / \ / H-C-O...H-O O...H-O-C-H / | | \ H H Although individual hydrogen bonds are weak, the large number of available OH groups in highly-hydrolysed PVA will result in a hydrated, 3-dimensional, gel, rather than a borate precipitate. The continual breaking and reforming of the bonds under low mechanical stress, and the large amount of water incorporated into the gel, are responsible for the rheological properties of the hydrated gel. Slime can be broken down by reducing the concentration of borate by titration with a strong acid, and details of such a procedure have been recently published .