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Author: Subject: I want to hear your favorite chemistry demonstrations
Scalebar
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[*] posted on 3-2-2017 at 06:35


Quote: Originally posted by Melgar  

Aluminum/gallium/indium alloy at 96:3:1 is air-stable, reacts vigorously with water to generate hydrogen, can be safely handled with bare hands, as long as they're dry, and even when they're wet, the worst that'd happen is a mild burn from the heat of the reaction.


Is that an alloy that can be home made? I've plenty of gallium and a frankly alarming quantity of aluminum powder.

Re: Igniting calcium - I put three or four pieces on a vermiculite tile and hit it with a pencil blow torch. It does take a couple of minutes to catch but it's lovely shade of red - if 'shade' is the right term for something so bright it's like taking a scarlet hammer to your retinas.
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[*] posted on 3-2-2017 at 16:28


Quote: Originally posted by Chlorine  
My absolute favorite demonstration is the formation of Aluminium tri Iodide.

3g of Iodine and 4g of powdered aluminum added to a wide mouthed crucible. Once thoroughly mixed, add enough water to wet the mixture. Since the reaction is extremely exothermic the excess iodine sublimes into a beautiful purple vapor.

Lovely! This was one of the demo experiments at the stsrt of our chemistry class in high school. It didn't ignite well, but after it was aided with a Bunsen burner, it went off with great vigour. Although the fume hood was closed right away, we enjoyed the slowly paling ocre stains on the ceiling for the remainder of that school year :)

A personal favourite is the chameleon reaction between solutions of Cr(III) and ammonium paramolybdate, which ends in an Er(III) like coloured solution.

What I love to demo is the boiling of tap water when pulling a vacuum. If you pull down to a mbar and wait untill boiling has ceased, the water will be around 15 centigrade. The influence of dissolved salts present in the water on the drop of the bp is just stunning.
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[*] posted on 3-2-2017 at 17:40


Aluminium in bromine looks neat but my favourite demo is sodium and lithium metals into liquid ammonia. I love the way these little blue tendrils reach out from the metal at first and then form that brilliant blue solution of solvated ions. When the metal first begins dissolving it looks awesome and it is equally cool to see a coppery mirror form when enough metal has been used.



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Melgar
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[*] posted on 4-2-2017 at 23:44


Quote: Originally posted by Scalebar  
Quote: Originally posted by Melgar  

Aluminum/gallium/indium alloy at 96:3:1 is air-stable, reacts vigorously with water to generate hydrogen, can be safely handled with bare hands, as long as they're dry, and even when they're wet, the worst that'd happen is a mild burn from the heat of the reaction.


Is that an alloy that can be home made? I've plenty of gallium and a frankly alarming quantity of aluminum powder.

Re: Igniting calcium - I put three or four pieces on a vermiculite tile and hit it with a pencil blow torch. It does take a couple of minutes to catch but it's lovely shade of red - if 'shade' is the right term for something so bright it's like taking a scarlet hammer to your retinas.

I've been making this alloy quite a lot recently, to test its usefulness in organic reductions. I just melt down the aluminum with a propane torch, then mix in eutectic gallium/indium (3:1 ratio, 15˚C mp) when it's molten, typically at a ratio of 20:1 or so. When it solidifies, the gallium and indium separate out along grain boundaries, which makes the resulting material very brittle. I can break it using two pairs of pliers easily.

Aluminum powder doesn't work for this though, at least not using the setup I have. The torch would blow your aluminum powder everywhere, and it's really hard to get the particles to melt together anyway. But if you have a kiln or can melt down your aluminum somehow, then it should work fine. However, I've found that 3004 aluminum alloy is much more reactive than every other alloy I've tried, probably because there's a small amount of magnesium in it. This is actually the same alloy that's in soda cans, but it's much easier to melt down those disposable aluminum serving trays, and I can get three 30-gram trays for $1 at my local dollar store. I usually twist them up into a rod shape, as tight as I can get it so that there aren't so many insulating air pockets, then hold the torch at the base while I push the rest of it into the molten aluminum puddle with a pair of pliers. I have a thread with pictures in the prepublication forum.

Incidentally, if you need any indium, I just got over a pound of it, and am selling it here for fifty cents a gram plus shipping from New York City.

[Edited on 2/5/17 by Melgar]
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[*] posted on 16-8-2017 at 12:55


I did this this morning, didn't amp up or modify the sound in any way yet it's incredible how loud a simple tube with some methanol in it can be. I'd put this up against the typical barking dogs almost, the ones with N2O or NO2 enhanced oxygen sources. It killed my ears even as small as it is. If you listen to it at half speed you can really hear the reverberation.

Barking Dog Chemistry Demonstration With Methanol
https://www.youtube.com/watch?v=gxtllHrFTjU

[Edited on 16-8-2017 by Morgan]
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[*] posted on 16-8-2017 at 15:44


Disappearing potassium permanganate:
Add a pitch of KMnO4 to 100 ml of water. Then add 10 ml of vinegar. Now ad some thiosulfate solution while stirring.
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[*] posted on 17-8-2017 at 01:07


Some simple precipitation reactions. Mixing colourless substances to form a coloured precipitate or to give different coloured precipitates. The only problem is the most striking ones use hazardous compounds :-

Lead salts + iodide (colourless) > lead iodide (yellow). This can then be warmed and some lead iodide will dissolve separating out in golden plates as the solution cools.

Silver nitrate + potassium chromate (yellow) > silver chromate (brick red)

Another one is the classic crystal garden setup. Dilute water glass down and drop crystals of coloured salts (copper, cobalt, iron etc) in and "growths" of tubes of silicate will slowly form in the solution.




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[*] posted on 17-8-2017 at 11:44


CaSO4 + aluminum powder is very powerful.
The CaSO4 is obtained from crushed plasterboard which I heated to 400 C te remove all the water and then powdered it.

I tried it yesterday. See here a video which is similar to a reversed rocket engine.

https://www.youtube.com/watch?v=HsZvbJInNCw

[Edited on 2017-8-17 by metalresearcher]




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[*] posted on 18-8-2017 at 19:58


I also do an annual demonstration for K-5 students, and although these aren't my favorites, they're quite popular among my audience:

Nitrogen triiodide
Flame color tests of various metal salts (I honestly hate doing this one, but they seemed to like it the year I did it)
Oscillating iodine reaction (aka "iodine clock"; this on e gets a great reaction, especially the time I didn't get it to initiate and I told them it must not have worked, and it near instantaneously turned back to elemental iodine while my back was turned, which is apparently hilarious to elementary schoolers)
Electroplating a quarter with copper (Dunno why that's amusing to them)
Showing the energy in sugar by burning KNO3/Sucrose
Those are pretty consistently a hit, although I only do this once a year.

As for my favorites, ETN synthesis and other nitrations are always fun, and catalytic synthesis of formaldehyde over copper or platinum is fun too.




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[*] posted on 17-10-2017 at 07:48


A cute little effect. Imagine enhancing it for a toy of some sort.
"I honestly have no idea how I made this. I was just experimenting around with empty tealights and pure ethanol and suddenly it started pulsing."
https://www.youtube.com/watch?v=HxsJna3tMF4
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[*] posted on 17-10-2017 at 09:38


Never actually seen this one, but it was described in an old Edgar Allan Poe story and I've always wondered if it was for real. Maybe somebody here knows.

Pour sulfuric acid into a red-hot platinum crucible and after a moment add a few drops of water.

The acid is supposed to boil off so rapidly it leaves the water behind as ice which can be quickly dumped out of the crucible before it melts.

I would be very reluctant to try this even if I had a platinum crucible for reasons that must be all too obvious (water poured into hot H2SO4, H2SO4 boiling off in great clouds, etc), but has anybody else heard of this other than from Poe?

Please don't just try this unless you've seen it before or really know what you're doing. It sounds like a recipe for disaster to me and I only have the word of a long-dead mentally unstable alcoholic and opiate enthusiast that it even works. (And even if he was right, some editor might have screwed up the details as this was just part of a short story and not a report in a scientific journal)

The story was: The Thousand and Second Tale of Scheherazaad (sp?)

On re-reading that post I realized something:
Boy, that was one hell of a disclaimer, wasn't it?

Comment added several hours later:
Posting this renewed my curiosity so I checked the original Poe quote and found that he describes Sulfuric acid as, "the most volatile of bodies", which it obviously isn't.

Perhaps he was confusing sulfuric acid with sulfuric ether, an old name for diethyl ether. I suppose ether poured into a red hot crucible might briefly do that thing where it skitters around on a bed of vapor (I forget what it's called technically, but that's what it looks like), and that adding the water might result in a change in surface tension or something that would make it flash off quickly cooling the water to the freezing point.

He does refer to the vapors given off as 'sulphurous', but maybe Poe, being no chemist, just assumed sulfuric ether would boil off into sulfurous fumes of some sort.

Of course he may have just been well into his second pint of Monongahela whiskey and made the whole thing up.






[Edited on 17-10-2017 by SWIM]

[Edited on 17-10-2017 by SWIM]
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[*] posted on 17-10-2017 at 09:44


Crystal garden in water glass, drop crystals of metal salts into water glass, and watch little towers grow from seemingly very little. Plus you get the different colours, i love colbalt ones but obviously not an environmentally friendly one.

Elephant toothpaste we did, we used 12% peroxide with MnO2 (i think), and just a tiny amount of decent washing up liquid. It was done in a large measuring cylinder and shot all over the place :D.

The other one i cant always get to work, is the super cold water in a bottle, (cant remember the term) then bang the bottle on a table and it freezes instantly.

super cooled water
https://www.youtube.com/watch?v=Fot3m7kyLn4
[Edited on 17-10-2017 by NEMO-Chemistry]

[Edited on 17-10-2017 by NEMO-Chemistry]
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[*] posted on 17-10-2017 at 10:33


Quote: Originally posted by SWIM  
Never actually seen this one, but it was described in an old Edgar Allan Poe story and I've always wondered if it was for real. Maybe somebody here knows.

Pour sulfuric acid into a red-hot platinum crucible and after a moment add a few drops of water.

The acid is supposed to boil off so rapidly it leaves the water behind as ice which can be quickly dumped out of the crucible before it melts.

I would be very reluctant to try this even if I had a platinum crucible for reasons that must be all too obvious (water poured into hot H2SO4, H2SO4 boiling off in great clouds, etc), but has anybody else heard of this other than from Poe?

Please don't just try this unless you've seen it before or really know what you're doing. It sounds like a recipe for disaster to me and I only have the word of a long-dead mentally unstable alcoholic and opiate enthusiast that it even works. (And even if he was right, some editor might have screwed up the details as this was just part of a short story and not a report in a scientific journal)

The story was: The Thousand and Second Tale of Scheherazaad (sp?)

On re-reading that post I realized something:
Boy, that was one hell of a disclaimer, wasn't it?

[Edited on 17-10-2017 by SWIM]


I remember reading the story, and figuring that he had no idea what he was talking about.




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[*] posted on 17-10-2017 at 16:07


I wonder if this property has something to do with the mystery. As an aside, the 1851 text doesn't mention sulfuric acid but rather sulfurous acid. And the boiling point of the said acid is nothing along the lines of sulfuric acid. Couple the below effect with an "insulating" Leidenfrost effect and maybe a frozen mass comes about in this way.

"When trying to concentrate the solution by evaporation to produce waterless sulfurous acid it will decompose (reversing the forming reaction). In cooling down a clathrate SO2 · 5.75 H2O will crystallise which decomposes again at 7 °C. Thus sulfurous acid H2SO3 cannot be isolated."
https://en.wikipedia.org/wiki/Sulfurous_acid


From 1851
https://books.google.com/books?id=PDFRAAAAYAAJ&pg=PA541&...

[Edited on 18-10-2017 by Morgan]
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[*] posted on 17-10-2017 at 16:19


Quote: Originally posted by Morgan  
I wonder if this property has something to do with the mystery. As an aside, the 1851 text doesn't mention sulfuric acid but rather sulfurous acid. And the boiling point of the said acid is nothing along the lines of sulfuric acid

"When trying to concentrate the solution by evaporation to produce waterless sulfurous acid it will decompose (reversing the forming reaction). In cooling down a clathrate SO2 · 5.75 H2O will crystallise which decomposes again at 7 °C. Thus sulfurous acid H2SO3 cannot be isolated."
https://en.wikipedia.org/wiki/Sulfurous_acid



From 1851
https://books.google.com/books?id=PDFRAAAAYAAJ&pg=PA541&...


Thanks, I bet that's the answer.
Even explains the 'sulphurous vapors' line that confused me.

The version I read was probably the result of some editor who didn't know about sulfurous acid assuming it was a typo for sulfuric.

Seems like there are several versions floating around out there for many of poe's stories.

[Edited on 18-10-2017 by SWIM]
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[*] posted on 17-10-2017 at 17:12


Near the bottom of the page
"*(5) Place a platina crucible over a spirit lamp, and keep it a red heat; pour in some sulphuric acid, which, though the most volatile of bodies at a common temperature, will be found to become completely fixed in a hot crucible, and not a drop evaporates- being surrounded by an atmosphere of its own, it does not, in fact, touch the sides. A few drops of water are now introduced, when the acid, immediately coming in contact with the heated sides of the crucible, flies off in sulphurous acid vapor, and so rapid is its progress, that the caloric of the water passes off with it, which falls a lump of ice to the bottom; by taking advantage of the moment before it is allowed to remelt, it may be turned out a lump of ice from a red-hot vessel."
http://xroads.virginia.edu/~hyper/poe/shehera.html

Summary
https://en.wikipedia.org/wiki/The_Thousand-and-Second_Tale_o...
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[*] posted on 18-10-2017 at 03:27


Sounds like he could be describing SO3 when he's talking about "sulfurous acid". After all, it's boiling point is what? 45C? This is all pre-IUPAC naming conventions of course, when both pure substances and mixtures could have any of a number of overlapping common names. I could certainly imagine hot SO3 reacting violently when coming in contact with a few drops of water.



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[*] posted on 18-10-2017 at 08:46


Quote: Originally posted by Melgar  
Sounds like he could be describing SO3 when he's talking about "sulfurous acid". After all, it's boiling point is what? 45C? This is all pre-IUPAC naming conventions of course, when both pure substances and mixtures could have any of a number of overlapping common names. I could certainly imagine hot SO3 reacting violently when coming in contact with a few drops of water.


I did wonder about that possibility too, but I had a hard time coming up with a way that that would produce ice. Seems to me the result would more probably be best described as a cloud of agony. Not as bad as the Nazis opening the Ark Of The Covenant in Raiders Of The Lost Ark, but still pretty nasty.

Hell, I've really derailed this thread, sorry. Maybe this Poe stuff should be split off and put somewhere more appropriate.
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[*] posted on 18-10-2017 at 10:10


Quote: Originally posted by SWIM  
I did wonder about that possibility too, but I had a hard time coming up with a way that that would produce ice. Seems to me the result would more probably be best described as a cloud of agony. Not as bad as the Nazis opening the Ark Of The Covenant in Raiders Of The Lost Ark, but still pretty nasty.

Could be sulfuric acid ice. That is, the SO3 is superheated, water is added, which not only adds heat, but messes up the whole superheating phenomenon. All the SO3 boils away at once, removing enough heat from the system to freeze the fraction of the SO3 that has been turned into H2SO4 by the water.

It's weird hearing it described in terms that aren't what anyone would use today, but that seems to be a good contender.




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[*] posted on 19-10-2017 at 09:16


Nitrogen triiodide has to be one of my favourite demonstrations. A tiny amount of solid that can detonate simply by dropping a feather on it, releasing a vast purple cloud of iodine vapour. Also along those lines, watching the direct deposition of iodine vapour is also cool. To a beaker is placed a gram or so of iodine and on top, a round bottom flask filled with ice cold water is placed. The iodine is heated so it sublimes, and as it comes into contact with the flask, 'hairs' of crystalline iodine form - this can also be done on a smaller scale using a test tube and boiling tube (image attached). This is also a great way to purify iodine.

IMG_0222.JPG - 191kB

[Edited on 19-10-2017 by LearnedAmateur]




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[*] posted on 19-10-2017 at 20:58


I found a nice demonstration that might be interesting, i intend doing the experiment this weekend. The experiment is from JCE, it uses magnetized bio char to remove Salicylic Acid and 4-Nitroaniline from water. However it might work at removing a food dye instead.

Sounds boring but basically you add the biochar to the coloured water, then use a magnet to remove the biochar and colour from the water.

The reference is
Karunanayake, A. G. et al. (2016) ‘Salicylic Acid and 4-Nitroaniline Removal from Water Using Magnetic Biochar: An Environmental and Analytical Experiment for the Undergraduate Laboratory’, Journal of Chemical Education, 93(11), pp. 1935–1938. doi: 10.1021/acs.jchemed.6b00154.

Might be neat if you can remove say blue dye from water with a magnet and should be cheap.



[Edited on 20-10-2017 by NEMO-Chemistry]

bio.png - 362kB
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[*] posted on 31-1-2018 at 09:18


Bird defeats Einstein
The Engineering of the Drinking Bird
https://www.youtube.com/watch?v=UCKC-QVcVn0
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[*] posted on 31-1-2018 at 10:15


Quote: Originally posted by Morgan  
A cute little effect. Imagine enhancing it for a toy of some sort.
"I honestly have no idea how I made this. I was just experimenting around with empty tealights and pure ethanol and suddenly it started pulsing."
https://www.youtube.com/watch?v=HxsJna3tMF4


Congratulations ...you just re-invented https://en.wikipedia.org/wiki/Pulse_detonation_engine

may be a good one to send to the SloMoGuys ?




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[*] posted on 31-1-2018 at 14:12


Quote: Originally posted by Morgan  
Bird defeats Einstein
The Engineering of the Drinking Bird
https://www.youtube.com/watch?v=UCKC-QVcVn0

Yay! Someone else is subscribed to engineerguy.
I like his stuff.




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[*] posted on 31-1-2018 at 15:16


Quote: Originally posted by j_sum1  
Quote: Originally posted by Morgan  
Bird defeats Einstein
The Engineering of the Drinking Bird
https://www.youtube.com/watch?v=UCKC-QVcVn0

Yay! Someone else is subscribed to engineerguy.
I like his stuff.



Related subject matter maybe of interest ...

"I used ordinary acetone as the working fluid. I also made some "bubblers" that worked at room temperature using evaporative cooling at the top end.
http://nfttu.blogspot.com/2009/04/methylene-chloride-and-dip...

Some sort of something here
https://www.youtube.com/watch?v=b9JFr6pEJco
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