Archive-name: sci/chem-faq/part4 Posting-Frequency: monthly Last-modified: 2 October 1997 Version: 1.16 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 [1], or the two volume Chemical Demonstrations - A Sourcebook for teachers by Summerlin and Ealy [2]. 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: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it (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.[3]. ]   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 [6], 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: lmar...@uc_link_.berkeley.edu (Lonnie C Martin) Date: 17 Feb 1993 Subj: Re: Growing a Silver Tree in Beaker?   In article <... This e-mail address is being protected from spam bots, you need JavaScript enabled to view it (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: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it (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 < This e-mail address is being protected from spam bots, you need JavaScript enabled to view it   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 de_script_ion 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,
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