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chemistry demonstrations


hermanntrude
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I am a new chemistry instructor at a college. I teach first year university transfer courses in chemistry and science.

 

I've been developing a list of demonstrations to provide throughout the year. So far i've got

 

  • elephant toothpaste (decomposition of H2O2 in presence of a catalyst and some dish detergent)-- requires a laboratory because of the mess
  • nitrogen triiodide-explosive decomposition. good demonstration of exothermic reaction and unstable compound. Also requires a laboratory since it gives off a large cloud of iodine and a bang loud enough to leave your ears ringing
  • barium hydroxide octahydrate and ammonium thiocyanate. Two solids mixed together create a lot of water which dissolves the other products of the reaction. Entropy driven and very endothermic. Requires a laboratory due to toxicity of barium hydroxide and the smell of the thiocyanate
  • ammonium dichromate combustion. Good fun but already included in the labs part of the course.
  • cobalt chloride equilibrium with complex ion. Also included in lab section of the course. good demo of le chatelier principle

 

Can anyone list any more? they need to be fairly safe and demonstrate something that's covered at first year level.

 

I'd be particularly interested in anything that could be done in a lecture theatre safely.

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Luminol / Cyalume make nice demos

 

KMnO4 and Glycerol is also interesting (the Delay before rxn is an attn grabber.

 

molten KClO3 and a jelly baby shows of O2 quite nicely.

 

Transition metal chemistry with different oxidation states (and thus colors) is fascinating also.

 

Ammonium hydroxide and HCl show an interesting Gas to Solid phase transition.

 

there are Zillions of neat things really ;)

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yes i was considering luminol, although the courses are fairly basic. It might fit somewhere although i don't think they actually cover luminescence... it's fun anyway, but i am trying my best to demonstrations for reasons, rather than for fun.

 

Not come across glycerol/KMnO4 before... redox, i suppose? flames or just spitting and smoke?

 

I've heard of the jelly baby one before. I'll probably do that sometime but might have to be next year. I came into the position in the middle of term so some topics were already covered before i got my chance.

 

I'm also going to do an oscillating reaction but we didn't have any malonic acid in the stores so i've ordered some. and some fresh H2O2 to make a better elephant toothpaste... Perhaps if i can buy a small enough quantity i'll get some potassium for next year's alkali metal demo.

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it is a redox yes, and after about 5-10 seconds it bursts into lovely purple flames.

 

the Spitting and "smoke" is likely the dehydration reaction of Conc sulphuric and sugar, also Fascinating to watch as this expanding black spongy mass grows with steam blowing out of every pore in it :)

 

to be honest though, unless you give us an idea of what this First year covers, all anyone can do is speculate as to what may be suitable.

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true, good point. Unfortunately, that'd take about a year :0)

 

I'm grateful for your ideas so far. keep them coming and i'll eventually have a list of good'uns.

 

I remember the sulphuric and sugar demo from high school. I'll have to do that some time.

 

bump (is that forbidden here?)

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I can recomend "Chemical Demonstrations: A handbook for teachers of Chemistry" v.1 and v.2 written by Bassam Z. Shakhashiri

 

ISBN 0-299-08890-1 (v.1)

ISBN 0-299-10130-4 (v.2)

 

A must for any Chemistry teacher

 

thanks. I'll see about getting it

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a more specific question:

 

Has anyone here ever added rubidium to water? Most chemistry instructors only go as far as potassium when demonstrating alkali metals with water. i want to try rubidium but want to stay safe. how much is safe to add at any one time? I know that it's not safe to store so i dont want to buy more than i can use at one time

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  • 1 year later...

I can't answer you question, but I'd like to ask: If I add sodium to water, and I take my class out doors in an open area, what would be good amounts of sodium to use: maybe, one small amount to get them excited, and then a larger quantity to really spice things up?

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a more specific question:

 

Has anyone here ever added rubidium to water? Most chemistry instructors only go as far as potassium when demonstrating alkali metals with water. i want to try rubidium but want to stay safe. how much is safe to add at any one time? I know that it's not safe to store so i dont want to buy more than i can use at one time

 

That's because Rb and Cs are generally very expensive in comparison and don't really offer much bang for your buck.

 

This page has videos of everything: http://theodoregray.com/periodictable/AlkaliBangs/index.html

 

^^^ yes, I realize he asked over a year ago, but just for reference.

 

As for the sodium, take a look at these videos and tell me if you think this is safe to do with a group of students: http://www.periodictable.com/Stories/011.2/index.html

 

The explosions scatter both unreacted sodium and lye everywhere, so plan on killing off a large patch of grass and building something to release the Na from a distance.

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I can't answer you question, but I'd like to ask: If I add sodium to water, and I take my class out doors in an open area, what would be good amounts of sodium to use: maybe, one small amount to get them excited, and then a larger quantity to really spice things up?

 

Ive used sodium and potassium. I've found that the potassium is more violent but much more predictable... the sodium can give you nasty surprises.

 

Generally what I do is this: cut off a chunk of metal about the same volume as a cube 3 or 4mm on a side, no more. Then put that chunk in some hexane to wash off the oil. Then take the original stock back into the flammables cupboard. Then get a large, plastic container of water, with a bit of phenolphthalein in it and put it behind my explosion guard. Then make sure my entire audience is standing well back and prepared, then put on my goggles and lab coat, then use some tongs to drop the metal in. The sodium has a tendency to explode if it melts onto the side of the container. If that happens, be prepared to wash molten sodium off your explosion guard. the potassium is much nicer because it burns with a lilac flame, but too much and it WILL go bang.

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