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woelen
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[*] posted on 27-12-2021 at 13:50
fun with acetylene


Right now, near the end of the year, you can buy calcium carbide in the Netherlands at many places for cheap. The intended use is for so-called "carbid schieten", which is an old tradition over here, where people take a big metal bucket (usually a milk churn, 30 liters or 50 liters), which is tightly sealed and in which a little hole is made in the bottom. They put in a lump of calcium carbide, a little water, and wait a while. Then they ignite the gas mix in the bucket, which explodes with a deafening report and the lid of the bucket is ejected over a distance of tens (or close to 100) meters. Right now, this is our fireworks substitute, because of a total prohibition of real fireworks in the Netherlands this year.

The k3wl in me revived and I decided to buy some calcium carbide (2.5 kg) and play with acetylene in an other way. Some really funny experiments, very good for demos:
- Take a lump of calcium carbide (20 grams or so) and put this under a glass jar, which is completely filled with water. A lot of gas is produced and the glass jar is filled completely with acetylene gas. Next, take a syringe, filled with chlorine and a pasteur pipette and assure that the tip of the pipette is in the acetylene and then _slowly_ press the chlorine into the acetylene. The effect is spectacular. The gas autoignites and burns with a very bright red/orange flame, which produces an incredible amount of soot. So, you have chlorine gas, burning in an atmosphere of acetylene. This experiment also can be done the other way around, by slowly pressing acetylene gas in an atmosphere of chlorine.
If both gases are mixed too quickly, then this leads to an explosion, which can be quite scary!
A nice, but much more violent variation of this experiment, which definitely must be done outside is the following:
- Take 100 ml of 10% HCl and put this in a big glass jar.
- Add 50 ml of 12.5% NaOCl, cover the jar loosely with a cap, and wait until you have a lot of Cl2.
- Remove the cap and throw a lump of 10 grams or so of calcium carbide in the acid and step back.
Bubbles of acetylene are formed at the calcium carbide, which, as soon as they reach the surface and are mixed with the chlorine gas, lead to miniature explosions with a lot of soot. Very often (but not always), the experiment ends with a fairly large explosion, which ejects most of the liquid from the big jar. Big billowing clouds of soot are produced as well.

Another, much less violent, but more useful, experiment is reacting acetylene with bromine. For this experiment, it is best to bubble acetylene gas through a dilute and slightly acidic solution of CuSO4 in order to remove impurities like PH3, H2S and NH3 and then bubble the purified gas through a solution, containing a lot of bromine. If this is done, then the color of the bromine disappears and many small pale orange droplets of heavy liquid separate from the solution. These droplets are made of CHBr2-CHBr2, with a slight excess of Br2 dissolved in them.
Another interesting experiment is dripping pure bromine in a jar, full of acetylene gas. The drop of bromine quickly disappears and is replaced by a white mist. This white mist is CHBr=CHBr if excess acetylene is used. Unfortunately you don't get a pure compound, you get two isomers (cis-CHBr=CHBr) and trans-CHBr=CHBr), and almost certainly you also get a little CHBr2-CHBr2. If you use excess Br2, then you only get CHBr2-CHBr2.
This reaction can be used to make brominated alkenes or alkane. I made a few drops of these, which collect as a blob at the bottom of the aqueous layer. I have no immediate use for these compounds, but it is interesting to see their formation and the formation of the white mist.
With a little Na2CO3, any excess Br2 can be destroyed and you get colorless drops of CHBr2-CHBr2 under the water. You can extract these drops from under the water and dry and distill this liquid. I did not do that.

The difference between the reactivity of chlorine and the reactivity of bromine is remarkable in this reaction. Chlorine cannot be used to chlorinate acetylene, it completely destroys the molecule, producing soot and HCl. Bromine reacts quickly, but not violently with acetylene. Even pure liquid bromine does not inflame (I tried by dripping a few drops of bromine into pure acetylene gas).
Maybe you can make the chlorinated compounds if the chlorine is not used as a gas, but dissolved in a suitable solvent (e.g. CCl4), but I did not try that.

In a final experiment, I made some gas mix, with appr. 2 volumes of O2 and one volume of acetylene. If bubbles of this gas mix are ignited, then you get a really loud bang, even from small bubbles. The theoretic optimum ratio is 2.5 : 1, but acetylene dissolves somewhat in water, so for maximum effect it is best to take only 2 volumes of oxygen to one volume of acetylene. In the time between bubbling it to the surface and igniting the bubbles some acetylene dissolves, hence the use of a little excess acetylene. BEWARE: Only use small bubbles (a few cm diameter) on the surface of some water with a little dishwashing soap in it. NEVER ignite mixes of acetylene and oxygen in a glass bottle or test tube if you value your eyes and fingers!!! The reaction of acetylene with oxygen is one of the most powerful reactions I have ever witnessed. An unconfined soap-bubble of a few cm diameter gives a really loud BANG when ignited. Nice demo-stuff!


[Edited on 27-12-21 by woelen]




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Metacelsus
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[*] posted on 27-12-2021 at 15:25


In the organic chemistry lab where I worked as an undergrad, someone once generated dichloroacetylene by mistake, which caused a small explosion. I'd recommend staying away from such things.



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[*] posted on 27-12-2021 at 16:15


Here is a comment courtesy of Science Direct at https://www.sciencedirect.com/topics/chemical-engineering/ac... :

"Acetylene reacts with active metals (e.g., copper, silver, and mercury) to form explosive acetylide compounds. Acetylene manufactured from calcium carbide can contain impurities such as phosphine and arsine that are responsible for the ethereal to garlic-like odor of commercial acetylene and pose a greater human health risk than acetylene alone. Maintaining acetylene levels below 3000 ppm can minimize these secondary toxic effects."

So, more "fun" in an energetic material sense from say the copper and silver forming explosive acetylides. However, I suspect, some of the latter, are more likely "discovered" post there incidental formation and subsequent rapid decomposition.

I further suspect that there are many "surprised" by the impurity sourced phosphine and arsine.

Personally, I am far less likely to be "surprised" by fireworks.
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[*] posted on 27-12-2021 at 17:07


Nice experiments! Speaking of experiments with acetylene, have you ever heard about linear acetylenic carbon? It's allotrope of carbon with straigh -C≡C- chain.

https://en.wikipedia.org/wiki/Linear_acetylenic_carbon




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[*] posted on 27-12-2021 at 23:26


Another experiment (to be performed outdoors !) if you have 30% (or even 12% H2O2):
If you have old plastic film canisters (metal of glass is too dangerous for shrapnel), fill it half with the H2O2, then put a few lumps of CaC2, as small as possible to get more surface in it, close the lid and QUICKLY throw it away. Wait and it will probably explode. The CaC2 should act both as a reactant and as a catalyst to decompose the H2O2, so both C2H2 and O2 will be formed in a confined space and due to the instability of pressurized C2H2 which probably will BOOM. Headphones or earmuffs required.

Note: This is theory, I have never done it.



[Edited on 2021-12-28 by metalresearcher]
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[*] posted on 28-12-2021 at 04:13


@Metacelsus: I also once made dichloroacetylene by accident, but that cannot be made from acetylene. Dichloroacetylene can be made from trichloroethene and NaOH, when mixed in such a way that there is quite some contact (e.g. in alcoholic solution). I once made this and as soon as this comes in contact with air, it ignites, giving a red flame with an amazing amount of soot.

@AJKOER: I know of the impurities of PH3, H2S and NH3 (no AsH3 I assume, otherwise I cannot imagine that many tonnes of this stuff would be sold in the Netherlands every December to private individuals). The amounts of PH3 and H2S are small, but noticeable. Especially the PH3 you can easily smell. These impurities can be held back with an acidified solution of CuSO4. PH3 is oxidized by the Cu(2+) ions, H2S forms an insoluble precipitate of CuS in a slightly acidic solution and NH3 is converted to ammonium ion. No copper acetylide is formed in acidic solution, the acetylene simply passes through the solution. I tried this and it works like a charm.

@metalresearcher: That experiment of yours sounds incredibly dangerous. What chance do you have that the thing explodes in your hand, before it is thrown away?

@Bedlasky: Interesting read about the linear allotrope of carbon. Unfortunately the Wiki-article only contains hints of possible methods for making this and for detecting this. Probably beyond reach of the average home scientist, but definitely worth looking at in more detail. Maybe more info can be found with a suitable internet search.




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[*] posted on 28-12-2021 at 04:48


Quote: Originally posted by woelen  

@metalresearcher: That experiment of yours sounds incredibly dangerous. What chance do you have that the thing explodes in your hand, before it is thrown away?


That is the reason I did not try it. I already thought it might be scary.
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[*] posted on 28-12-2021 at 08:31


Neat stuff! I once saw a version of the first demo, which was carried out in a long, sturdy glass tube. Carbide was tossed in and chlorine slowly bubbled in from a tank, forming underwater explosions as the bubbles merged. The headspace of the tube not occupied by water would accumulate gas and every now and then it would go WOOMP. The size/safety of those big explosions would probably be modulated by how full the tube was.



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[*] posted on 28-12-2021 at 11:37


Quote: Originally posted by woelen  

@Bedlasky: Interesting read about the linear allotrope of carbon. Unfortunately the Wiki-article only contains hints of possible methods for making this and for detecting this. Probably beyond reach of the average home scientist, but definitely worth looking at in more detail. Maybe more info can be found with a suitable internet search.


In 1999, it was reported that copper(I) acetylide (Cu2C2
), after partial oxidation by exposure to air or copper(II) ions followed by decomposition with hydrochloric acid, leaves a "carbonaceous" residue with the spectral signature of (−C≡C−)n chains with n=2–6.

Finally, the oxidation of copper acetylide in ammoniacal solution (Glaser's reaction) produces a carbonaceous residue that was claimed to consist of "polyacetylide" anions capped with residual copper(I) ions,

Cu+ C−(≡C−C≡)nC− Cu+.
On the basis of the residual amount of copper, the mean number of units n was estimated to be around 230.


This should be easy to do in home setting.

[Edited on 28-12-2021 by Bedlasky]




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[*] posted on 28-12-2021 at 11:59


I did yet only the boom version of acetylene experiment decades ago. I filled 2,5 L PET bottle with O2 and little of water, inserted a wire through 2 holes in the cap and glued the holes. On the place outside I unscrewed the cap, tossed a little of CaC2 into the bottle, screwed the cap. It did not ignite spontaneously after few minutes so I used a battery and wire to trigger the detonation.
My father used to fill plastic bags of big volume like 50 L with acetylene and O2 from welding tanks and ignited that with a long piece of paper but that was prior I was born, I know that only from his talks.
Now I would like to do something more chemical like C2H2+2Br2 and maybe some condensations with ketones and aldehydes like acetone, acetaldehyde, formaldehyde. And maybe reaction with 100% HNO3 to tetranitromethane.




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[*] posted on 28-12-2021 at 13:08


If you have a tank of oxygen, ordinary methanol makes a pretty good "fuel/air" bang in leu of acetylene. I remember dissolving a silver dollar in nitric acid and making silver acetylide long ago, watching a paper pulp looking white substance form from the bubbles of acetylene rising up in the silver nitrate solution.
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[*] posted on 29-12-2021 at 04:54


Quote: Originally posted by Bedlasky  
Quote: Originally posted by woelen  

@Bedlasky: Interesting read about the linear allotrope of carbon. Unfortunately the Wiki-article only contains hints of possible methods for making this and for detecting this. Probably beyond reach of the average home scientist, but definitely worth looking at in more detail. Maybe more info can be found with a suitable internet search.


In 1999, it was reported that copper(I) acetylide (Cu2C2
), after partial oxidation by exposure to air or copper(II) ions followed by decomposition with hydrochloric acid, leaves a "carbonaceous" residue with the spectral signature of (−C≡C−)n chains with n=2–6.

Finally, the oxidation of copper acetylide in ammoniacal solution (Glaser's reaction) produces a carbonaceous residue that was claimed to consist of "polyacetylide" anions capped with residual copper(I) ions,

Cu+ C−(≡C−C≡)nC− Cu+.
On the basis of the residual amount of copper, the mean number of units n was estimated to be around 230.


This should be easy to do in home setting.

[Edited on 28-12-2021 by Bedlasky]

It might be possible to do this in a home setting, but how do I know that I don't have simply some wet soot? if the material you get cannot be distinguished from ordinary black soot without equipment to get a spectral signature of the material, then I consider it not really worth while to do at home. There must be something special, which can be observed.




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[*] posted on 29-12-2021 at 10:04


Karbidschießen!

Here, they prohibited fireworks too, second year in a row.... the over 300 year old fireworks factory here has to close now.... :(

This sounds like a fun alternative and once again the dutch are a nose length ahead of us :D




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[*] posted on 29-12-2021 at 12:50


I once was convinced by a friend from the east of the Netherlands carbid schieten was a good thing to do in within the singels of Leiden. Well, it was fun to do, twice after the first shot was shit :D then we almost blew out the single layer windows across the water.

You can overdo it.

https://youtu.be/aIrWH3BQ1FI
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[*] posted on 29-12-2021 at 19:20


Quote: Originally posted by woelen  

A nice, but much more violent variation of this experiment, which definitely must be done outside is the following:
- Take 100 ml of 10% HCl and put this in a big glass jar.
- Add 50 ml of 12.5% NaOCl, cover the jar loosely with a cap, and wait until you have a lot of Cl2.
- Remove the cap and throw a lump of 10 grams or so of calcium carbide in the acid and step back.
Bubbles of acetylene are formed at the calcium carbide, which, as soon as they reach the surface and are mixed with the chlorine gas, lead to miniature explosions with a lot of soot. Very often (but not always), the experiment ends with a fairly large explosion, which ejects most of the liquid from the big jar. Big billowing clouds of soot are produced as well.

I have a version of this in one of my books.
Page 164, demonstration 101.
Enjoy.
(And there are a lot of other cool things in that book too.)

Attachment: Chemical Demonstrations Resource Book 2.pdf (6MB)
This file has been downloaded 92 times

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[*] posted on 30-12-2021 at 05:27


Quote: Originally posted by metalresearcher  
fill it half with the H2O2, then put a few lumps of CaC2,
Note: This is theory, I have never done it.

In my mid-teens (c1970) a friend and I, working in his bedroom, made a small oxy-acetylene torch,
H2O2 with MnO2 in one side arm test tube
and CaC2 with H2O in another,
rubber tubes led the gasses to a drawn out glass tube as a torch,
very interesting, and lots of things got burned or melted.

I had the 'genius' idea of putting CaC2 in H2O2 guessing that we would get a usable oxy-acetylene mix.
It worked !
A beautiful flame, that got noisier and noisier and smaller and smaller ...
we both instinctively turned away just before the BOOM !
The test tube and the beaker it was resting in turned to shrapnel.
Amazingly neither of us were hurt,
but we had quite a lot of glass shards to clean up.
Definitely "DO NOT TRY THIS AT HOME" ... OR ANYWHERE, EVER.




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[*] posted on 30-12-2021 at 14:16


What you need is some translucent or clear wire sleeving several meters long with a ID of about a millimeter. Fill with the oxygen acetylene mixture. Ignite one end and the flame propagates along the tube not so fast that it can be easily seen.

You can also terminate the sleeving in a small plastic bag also filled with the gas mixture so you get a bang when the flame reached the bag.




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