spong
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Weird bromine contaminant
Hi  I made some bromine yesterday by bubbling chlorine through KBr solution, I
distilled it today and noticed a weird solid forming in the receiving flask, as each drop of bromine came over, it would hit the pile of solid and add
to it, at first I thought it might have been the bromine freezing as it was in a salt ice bath.
I ended up having to redistill it after I forgot to let the boiling flask cool and added a boiling chip and the Br+KCl water boiled over into the
receiving flask so I dumped the solid plus the rest of the bromine back into the flask and started again I distilled it again and noticed the solid
forming at the end of the condenser as well as a little bit floating in the bromine.
What on earth is this stuff :/
It's hard to see but a little bit of it ended up in the receiving flask again, it looks like lumps on the surface of the liquid in the reflection from
the light.
Sorry about the blurry photos, it was hard to hold the camera steady, I had to hold my breath whenever I went into the shed because it stunk of
bromine.
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woelen
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I think it is just plain water. I also had this when I distilled bromine. Water is much less dense than bromine and hardly is soluble in it (only
0.03% by weight can be dissolved in bromine, the other way around the solublity is appr. 3.5% by weight). The water floats on it and also contracts
into spheres, which look like solid particles. When the bromine is swirled, then the water droplets stick to the glass.
At the temperature at which bromine boils over (almost 60 C), also quite some water vapor goes with the bromine (just take a beaker of water at 60 C,
you'll see a lot of steam above this beaker, indicating that quite a lot of water vapor escapes from this liquid). If you want dry bromine, then shake
the bromine with some concentrated H2SO4 and redistill. You can also keep the bromine under the H2SO4.
Have a look at this webpage, which I wrote about bromine distillation. It also contains a picture of the receiving flask with the water droplets,
which look like some solid:
http://woelen.homescience.net/science/chem/exps/raw_material...
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spong
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I thought it could have been water or ice but when I first distilled it I had a problem with suckback (I was trying to bubble any excess bromine gas
through cold water to get some bromine water for testing for alkenes) so some water made it back into the receiving flask and the solid was still
there, just under water the whole time.
Plus if it was just water it shouldn't have formed that clump at the end of the condenser, it's probably a bit hard to see in those pictures. I'm also
quite sure the lump is getting smaller.
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woelen
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Try to make more clear pictures. From the pictures you have now it is not possible to see what you really have. Is the material colorless? If the
solid exists under water, then it definitely is not water.
How did you make the chlorine? Could it be that some other compound is formed as well, which is bubbled through the solution of KBr? Is your
KBr-solution a pure solution in clean water?
If the material is very cold, then the solid also could be bromine hydrate. This is a solid compound, but it only is stable up to 10 C or so. If you
heat the bromine to over 25 C then surely all of the bromine hydrate is destroyed and split into bromine and water.
If it is not bromine hydrate nor water and if all of your chemicals, including the bubbled Cl2 are pure, then I have no clue anymore.
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spong
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I went out to then and it was gone, there's nothing but bromine fumes in there. I couldn't see the colour of it, it was either red/brown or another
colour which was overpowered by the bromine.
Bromine hydrate could make sense, it would have decomposed once the cold water was gone from the condenser and it warmed up a bit, decomposing back
into bromine and water. I think the lump is still in the liquid bromine but it could just be blobs of water, I'll squirt some sulfuric acid in on top
tomorrow and see if it is.
I used the bromine from the lump decomposing to make bromine water by blowing in one end of the condenser and bubbling the bromine/air from the vacuum
adapter through water and there's nothing left in there but water.
The chlorine gas was from HCl and Ca(OCl)2, not the best way to do it but I didn't want to waste my sulfuric acid.
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woelen
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Your way of making Cl2 is perfectly OK for this purpose. There may be some CO2 in it as well (due to calcium carbonate contamination in the calcium
hypochlorite), but that does no harm in your process. CO2 simply will escape to the air.
Was the water going along your condenser very cold as well? That could explain the formation of the solid blok of material instead of drops of water.
In my distillation process I just used tap water for cooling and that means that the temperature will not be below 15 C or so. This, however, is
perfectly suitable for condensing bromine.
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spong
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Ohh yes that would explain it, I used salt, ice and water pumped from the foam box the bromine flask was sitting on in that photo. I thought I'd try
to minimize the amount of bromine escaping. Of course it didn't matter when I was stupid enough to throw a boiling stone into hot bromine water  bromine water, gas and KCl shot straight out the top, somehow missing my hand
luckily.
I'll try a bigger batch soon once the uni homework is out of the way and I have some way of storing it.
Edit: I added the sulfuric acid, the lumps in the bromine were indeed water. Thanks
[Edited on 12-8-2010 by spong]
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