Nice experiment with bromine

[woelen]

Last week I made some KBrO3 by means of electrolysis of NaBr and crystallizing this with KCl. See this thread on SFN:

 

http://www.scienceforums.net/forums/showthread.php?t=16254

 

This stuff is too violent for pyro-experiments, so I searched for another use of this. I converted this stuff to pure bromine by adding NaBr and hydrochloric acid and the resulting bromine I collected in a small vial:

 

http://woelen.scheikunde.net/science/chem/compounds/bromine.html

 

Unfortunately I see no good way to store it for any length of time, so I used it for experiments. One of the experiments is so nice, that I want to share it with others:

 

http://woelen.scheikunde.net/science/chem/exps/Al+Br2/index.html

 

If you attempt to repeat this experiment, please be VERY careful. It is a dangerous experiment, if not performed in the right way. You are warned. Safety info is added in the experiment description on the page.

[silkworm]

I witnessed this about a month ago and it is pretty neat. Just stay cool if it doesn't go right away and proceed with caution.

 

If you've never witnessed liquid bromine too, it's truly something to behold. It's nasty stuff reminiscent of chlorosulfonic acid which is the nastiest stuff I've ever worked with. Be careful with it.

 

Can't you just store the bromine in a capped "potion" bottle? (If that makes sense) That's how we keep it in our lab and it works pretty well. You just want to keep it cool to keep the lid on.

[RyanJ]

Can't you just store the bromine in a capped "potion" bottle? (If that makes sense) That's how we keep it in our lab and it works pretty well. You just want to keep it cool to keep the lid on.

 

Yes you can - its very hard to store in any because easily vapourises and seeing as it vapourises easily you see the problem...

 

@woelen: Sounds like an interesting experiment, I'll either try it in school or when my new chemical equiptment and supplies arrive I have some Bromine in an ampoule and its pretty wierd stuff its also unique in that its one of only two liquid elements and the only non-metalic liquid one!

 

Cheers,

 

Ryan Jones

[akcapr]

Its also very corrosive, after time it tends to corrode caps. My teacher at school spilled some because over a few years the bromine ate away at the seal.

[jdurg]

Yeah, bromine will eat through typical caps. The ONLY way to store it without any fear of it eating through its container is to seal it in a glass ampoule. Over time, it will eat through any cap and eventually leach out as it evaporates very readily forming a very corrosive and hard to contain gas. I know this from experience as I had bromine eat its way through two containers, one of which was designed for bromine storage. (I ordered quite a bit of bromine from a seller on E-Bay a few years ago and when the bromine arrived it was perfectly fine. A few days later, I noticed a strange stench coming from where I was storing it and could see the bromine vapor leaching out. I quickly contacted the seller who overnighted a new bottle with a teflon cap and various other 'bromine stopping' measures. The bottle arrived the next day and I made the transfer, but the bromine STILL leached through the cap and was corroding the metal container it was then stored in. I finally just wound up sealing a few mL in an ampoule and trading the rest of my bromine for some harder to get elements).

 

The other way to store bromine is to solidify it. If you keep it in an openable container, just store it inside another container in a freezer. As a solid, it's much easier to store.

 

BTW, if you wind up with more Br2 that you want to get rid of, try adding a small piece of Na or K to the bromine. You'll REALLY see a neat reaction take off there.

[woelen]

BTW, if you wind up with more Br2 that you want to get rid of, try adding a small piece of Na or K to the bromine. You'll REALLY see a neat reaction take off there.

I have used up some more bromine in an experiment with phosphorous . Really spectacular.

 

http://woelen.scheikunde.net/science/chem/exps/P+Br2/index.html

 

I now have 0.5 ml left. I'll consider the sodium experiment.

[woelen]

I've done the experiment by adding freshly cut sodium metal to bromine. Surprisingly, no reaction at all. The sodium is completely wetted by the bromine and then remains floating on the bromine.

 

Next, I added a very small drop of water. If that is done, then the sodium reacts very violently, with fire-like things and little explosions. Probably the bromine makes the reaction between sodium and water more violent.

 

But, very surprising to see that sodium and bromine do not react at all.

[akcapr]

i think the oxide layer screwed thigns up. My teacher did the exact thing and it worked fine. It may take a while sometimes tho, just need somehtign to get it going.

[woelen]

i think the oxide layer screwed thigns up. My teacher did the exact thing and it worked fine. It may take a while sometimes tho, just need somehtign to get it going.

No, I don't think so. In the meantime I have done some studies on this subject in my book "Chemistry of the Elements" by Earnshaw and Greenwood. This book states that sodium metal can be stored in liquid bromine indefinitely, as long as no moisture is present. I was surprised to read about this, but my observations perfectly confirm this.

 

A very similar thing exists for many other reactions. Another example on my website is the reaction between iodine and magnesium and as far as I remember, Jdurg's experiment with sodium and iodine also required some water to start the reaction (or heating).

 

My experiment: http://woelen.scheikunde.net/science/chem/exps/mg+iodine/index.html

Jdurgs experiment: http://www.chemicalforums.com/index.php?op=articles;id=22

 

In my experiment I also said, that the piece of sodium was freshly cut. I cut a small piece from a larger piece, rinsed it in low boiling ligroin (40 - 60 degrees C), took out the piece of sodium, allowing the ligroin to evaporate (just takes seconds) and then put it in the bromine. So, it was not heavily oxidized (at least not at one side).

[jdurg]

I'd have to take a look into the reaction between bromine and sodium oxide/hydroxide as the sodium metal will react immediately to form an incredibly thin layer of Na2O on the surface of the metal as soon as you expose it to air. Even if it's just for a few seconds, in the time it takes to wipe off the oil and move the sodium into the bromine, a layer of oxide will form. To really check out whether it's the oxide formation or not, you would need to cut a piece of sodium metal underneath some bromine. However, that could be a VERY dangerous prospect so you may want to avoid that.

 

Another thing to do is to make the sodium molten, and then add the bromine. When I did my NaI synthesis experiment, there were two ways to get the reaction going. One was to add one tiny speck of water, and the other was to heat the metal up to the point of melting. Once molten, adding one tiny crystal of iodine got it roaring. If this is the same as with bromine, then you should be able to test the theory out.

 

If there is any hydroxide on the surface of the metal (which again can form in an instant if there is water vapor in the air), then the halogen will just react with the hydroxide and form a hypo-halogen ion which can further protect the surface of the metal.

[woelen]

Now I first need to make new bromine. I used up my last small amount of bromine in an experiment with selenium. It is good that all bromine is gone again. It is nasty stuff on storage, as jdurg stated already.

 

If I make bromine again, then I'll try to see what happens if I add it to molten sodium metal. Cutting sodium metal under a thin layer of bromine does not seem a very wise thing to me. Being with my nose over all these fumes and having the risk that the sodium/bromine mix bites at me... no, not this time .

 

Right now, I've had a lot of fun with just 1 ml of bromine . My final experiment with the selenium also was very nice. Adding selenium to bromine results in a violent reaction (while sulphur only reacts very slowly in the course of a day). The reaction product is a rust-like solid powder, SeBr4. With a little heating, driving off all excess bromine, a nice dry powder of SeBr4 can be obtained and then it really looks like rust, brown with an orange hue.

 

When SeBr4 is added to water, then it dissolves, leaving a colorless solution with H2SeO3 and HBr in it. When some Na2SO3 is added, again amorphous red selenium is produced. This is not the way to make red selenium, but it is very interesting to have made a strange compound like SeBr4 and seeing this as a pure compound.

 

It really is a pity that bromine is so bad on storage, otherwise I would make much more. You only need NaBr, electrolysis and a little acid.

 

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Yet, a nice suggestion, which does not require isolation of liquid bromine.

 

Make a solution of NaBr or KBr and add some dilute hydrochloric acid.

Add some bleach, such that the liquid becomes deep red and red vapors are above the liquid.

Carefully tap a small amount of red phosphorous into the red vapor. The phosphorous ignites.

 

@Jdurg: A similar experiment can be done with chlorine gas. Take a very small pinch of your red P (just 10 mg or so, not more) and tap this in a bottle with some chlorine gas in it. Quite spectacular. The chlorine does not need to be pure. This experiment is also on my website: http://woelen.scheikunde.net/science/chem/exps/P+Br2+Cl2/index.html .

[jdurg]

Yeah, I would also not want to cut sodium under bromine. If my hypothesis that the reaction is stopped by the ultra thin coating of sodium oxide is true, once the pure metal is exposed to the bromine it will rapidly react and you may not be able to get away in time before the bromine is flung onto your skin. In addition, the bromine would probably react with whatever metal your cutting instrument is made out of.

 

With the molten sodium, just be very careful. You may want to melt the sodium in a heat resistant test tube with argon gas sitting over the top of it. (This way the sodium doesn't ignite due to H2O and/or O2 in the air). When you add the bromine just do it one drop at a time. The one problem you may run into is the bromine vaporizing before it can come in contact with the sodium. I myself would also try out this experiment, but my bromine is sealed in a glass ampoule and I also don't have a good place to do any vapor containing experiments as winter is approaching and it's starting to get too cold outside.

 

If you want to have a nice supply of bromine quickly available, I'd suggest getting a small little freezer for your chemicals. Bromine solidifies at 266 K, so if you make a good deal of it you can keep it in a freezer where it exist as a solid and be MUCH less prone to eating through everything. When you need to use some of it, just let it liquify, extract what you need, and place it back in the chemical freezer.