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Author: Subject: Bromine from mostly OTC chemicals
woelen
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[*] posted on 11-8-2011 at 12:39
Bromine from mostly OTC chemicals


A few days ago I made some PBr3 and this used up a lot of my bromine, so I decided to replenish my stock of bromine somewhat. This time I thought it would be a good idea to use only standard chemicals, which can be purchased at a hardware store, swimming pool place and which does not depend on the availability of strong acids like H2SO4 or oxidizers like chlorates or bromates. Just NaBr and NaHSO4 (pH-minus for swimming pools) and cheap equipment such as graphite rods and household glass jars.

From 100 grams of NaBr and 150 grams of NaHSO4 I could make appr. 60 grams of bromine (this is a yield of 75%).

http://woelen.homescience.net/science/chem/exps/OTC_bromine/...

Unfortunately I had to cheat a little bit, I also needed a few 100's of mg of potassium dichromate (or any other dichromate or chromate), but this little amount of dichromate is the only really non-OTC material I needed. This little amount is not part of the reaction, but it is essential for the electrolysis process described in the web page.

I hope that this write-up helps other people to make such an interesting chemical like Br2 from standard stuff and that this makes Br2 a more accessible chemical for home chemists.




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blogfast25
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[*] posted on 11-8-2011 at 12:45


Nice write up, as per usual :)
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MrHomeScientist
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[*] posted on 11-8-2011 at 13:34


Very nicely done! I love bromine and have for a long time wanted to make some for my element collection. So, I'm very interested in synthesis routes. The only reason I haven't tried the distillation method yet is because I don't have a fume hood, and I dont want to mess with all that Br vapor, even if I do it outside.

This method looks great for me because, as you say, it produces very little fumes (and I have all the materials!). Of course when the acid is added you'll get some Br gas, but this seems much more manageable to me than a distillation kit filled with the vapor. I'll have to try this as soon as I get a chance.

When I seal it in an ampoule for display, should I chill the bottom of the ampoule while sealing the neck? Or would that cause enough heat stress to break it? I want to minimize fuming while I seal it up.
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sternman318
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[*] posted on 11-8-2011 at 21:51


Can you not also make bromine from sodium bromide, sodium bisulfate and hydrogen peroxide? It is less work intensive, atleast when it comes to the set up. However, when I had done this ( with very diluted sulfuric acid), the bromine was dissolved in the water and I had bromine water instead :P It is interesting that yours collected together on the bottom...
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[*] posted on 12-8-2011 at 06:35


Very Nice! Great idea using electochemistry to create the correct ratio of bromide/bromate in situ.

Yes you can use hydrogen peroxide, Magpie has a method in the prepublications section. His reaction is very exothermic and the bromine distills from the water into the flask. Woelen's method recovers 70% of the bromine, the rest is dissolved in the water

Using bisulfate might cause solubility problems with sodium sulfate, so make sure there is enough water. Don't want to heat it, bromine vapors!




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sternman318
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[*] posted on 12-8-2011 at 07:35


Ah, I skimmed but happened to not read that part! So I guess elemental bromine has a solubility level in water, for some reason that never crossed my mind! I always thought I would have to do a distillation to get any pure bromine.

EDIT: After reading Magpie's method, people mention disliking the H2O2 method because other methods yield bromine that can be pipetted out. Why would the H2O2 method yield bromine dissolved in water, and other methods yield bromine that is seperated?
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[*] posted on 12-8-2011 at 07:49


Quote: Originally posted by sternman318  
...
EDIT: After reading Magpie's method, people mention disliking the H2O2 method because other methods yield bromine that can be pipetted out. Why would the H2O2 method yield bromine dissolved in water, and other methods yield bromine that is seperated?


Many people used OTC 3% H2O2, which brings a _lot_ of water into the mix. Given Br2 solubility in water of about 3.4 G / 100 g H2O, there is enough water to dissolve most if not all t he Br2 produced.
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woelen
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[*] posted on 12-8-2011 at 10:00


Another issue is that really all bromide must be converted to bromine. I also mention this in my web page in which I really urge people to assure that sufficient bromate is produced, such that on acidification no unreacted bromide remains in solution. Bromine dissolves in water much more than 3.4 gram per 100 ml if bromide is present. The complex ion Br3(-) is formed in that case. Many attempts at making bromine fail due to the presence of unreacted bromide.

Using sodium bisulfate did not cause any solubility issues in my experiment. No crystals of Na2SO4 were formed. But even if such crystals are formed, this is not a real issue. These crystals will float on top of the bromine layer and the bromine still can be isolated easily.

If you want to put bromine in an ampoule, then there is no need to chill the bottom part of the ampoule, just be sure that the flame does not go below the area which has to be melted and sealed.


[Edited on 12-8-11 by woelen]




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[*] posted on 12-8-2011 at 10:17


That is pretty neat. Looks quite simple, and a nice way to produce bromine for immediate use.

Storing that stuff in anything else than sealed glass ampoules is too complicated for me. Even if I had blank ampoules to play with, my glasswork skills are less than average and I feel that I would probably make an awful corrosive Hazmat mess rather than making lovely sealed containers for elemental Br. LOL

Robert




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[*] posted on 12-8-2011 at 12:02


Good point about solubility and complete conversion. An excess of bromate would be beneficial, it would decompose back to bromide with acid so no lost yield.

A flint glass tube sealed at both ends would make for a sturdy sample. Ampoules are pretty flimsy but the neck snaps off cleany if you actually need to use it. Check out Myst32YT's channel on youtube for a video of bromine




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[*] posted on 12-8-2011 at 13:44


Looks like a good method, any thoughts about running longer to isolate the Bromate?
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woelen
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[*] posted on 13-8-2011 at 06:29


When you want to make bromate, then it is easier to start from KBr instead of NaBr, due to lower solubility of KBrO3. The procedure for that is described in another web page on my website:

http://woelen.homescience.net/science/chem/exps/KBrO3_synth/...




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[*] posted on 13-8-2011 at 07:52


Nice writeup, woelen. I've been running an optimised chlorate cell and would love to give this a try after the current batch is done.

Is it OK to store the filtered bromate liquor for a few weeks or months or will it degrade? I have serious doubts about my ability to store Br2 in my climate and lack of good storage bottles. It wouldn't be so bad to acidify and draw out the Br2 as needed, though - if the bromate liquor will hold up in storage.

Tank
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[*] posted on 13-8-2011 at 09:41


Br2: freeze it (-18 C), it's solidifies at about -7, IIRW. Wrap tightly closed bottle in a couple of freezer bags and put it with the frozen lasagne. Frozen Br2 has low vapour pressure, like most solids...
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[*] posted on 13-8-2011 at 10:45


Excellent write-up, I will be sure to give this a try in the future! Can't right now, as my storage equipment is lacking, so any bromine I need, must be made immediately before the experiment necessary. Thanks woelen!



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[*] posted on 14-8-2011 at 14:23


Walmart has 1L bottles of 30% NaBr for spas. This would be a perfect feedstock.

I really like the idea of having an instant source of bromine. Just add acid!




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woelen
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[*] posted on 15-8-2011 at 01:21


Quote: Originally posted by m1tanker78  
Is it OK to store the filtered bromate liquor for a few weeks or months or will it degrade?

Yes, it is OK to store the filtered bromate liquor. You can keep it for years without degradation. I would add a few granules of NaOH to this liquor before storage, just to make it slightly alkaline (only slightly, so only add a few prills of NaOH). This slightly alkaline liquid does not give off any fumes and can be kept around in any decent bottle. Adding acid then releases the bromine.




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