Sciencemadness Discussion Board - Separating bromine gas from water vapor

Separating bromine gas from water vapor

Cou - 26-10-2013 at 12:50

I was able to make bromine by sodium bromide and concentrated sulfuric acid, and now it's brown gas, but it is also suspended in water vapor and when i put the flask in the freezer, it doesn't liquefy.

vulture - 26-10-2013 at 12:54

Can you be a little more specific about what's going on: reaction conditions and amounts of reagents?

Cou - 26-10-2013 at 13:04

I'm too lazy to use stochiometry, so first I poured in some sodium bromide, then sulfuric acid on top of it. It made this cloudy brown gas, which I assume is bromine and water vapor, and when I put it in the freezer, the bromine didn't condense.

Pyro - 26-10-2013 at 13:29

That's not the attitude to have when you are making Br2 (look who's talking

)
how dark is your gas? can you post a pic?

deltaH - 26-10-2013 at 13:30

Hi Cou, you can't make bromine that way, you would have made hydrogen bromide gas which only liquefies at -86.9C!

To make bromine, you need oxidising conditions. Your equation is:

H2SO4(l) + NaBr(s) => NaHSO4(s) + HBr(g)

You should be able to dissolve the gas in water to form hydrobromic acid.

[Edited on 26-10-2013 by deltaH]

bismuthate - 26-10-2013 at 13:32

I believe that that makes HBr not Bromine. Also' please do that outside not inside.
Try NaOCl+NaBr+HCl
EDIT oops deltaH posted while I typed sorry.

[Edited on 26-10-2013 by bismuthate]

[Edited on 26-10-2013 by bismuthate]

kristofvagyok - 26-10-2013 at 13:34

Quote: Originally posted by Cou

I'm too lazy to use stochiometry

Maybe it would be a good idea for you to study a bit more chemistry than messing with chemicals.

deltaH - 26-10-2013 at 13:37

If I'm not mistaken, pyro here is SM's resident bromine making expert

So ask nicely...

@bismuthate... yeah don't you just hate it when that happens? I know I do!

[Edited on 26-10-2013 by deltaH]

Pyro - 26-10-2013 at 13:38

You can make Br2 with NaBr and H2SO4.
it proceeds like this:
NaBr + H2SO4 -> Na2SO4 + Br2 + H2O + SO2
H2SO4 + NaBr -> NaHSO4 + HBr
2SO2+2H2O+2HBr->H2SO4+2Br2
If i'm not mistaken.
but lots of NaBr is wasted as HBr. It's a very inefficient method

CORRECTION:
2NaBr + 2H2SO4 -> Na2SO4 + Br2 + 2H2O + SO2
H2SO4 + NaBr -> NaHSO4 + HBr
2SO2+2H2O+2HBr->2H2SO4+Br2

[Edited on 26-10-2013 by Pyro]

deltaH - 26-10-2013 at 13:42

Ah ok, so sulfuric acid acts as the oxidant? Interesting, always thought that was kinetically useless. Hmm... well I learnt something new today... sorry cou looks like you can make some bromine that way.

Pyro, there's a problem with your last equation...

Quote:

2SO2+2H2O+2HBr->H2SO4+2Br2

Your first equation is also not balanced.

Ok, just checked out reduction potential tables, for sulfurc acid:

SO42- + 4 H+ + 2 e− <=>SO2(aq) + 2 H2O E=+0.17V

For bromine:

Br2(l) + 2 e− <=> 2 Br- E=+1.066V

So I don't see how you can make any bromine from the reduction of sulfuric acid to SO2?!

[Edited on 26-10-2013 by deltaH]

woelen - 26-10-2013 at 13:48

No, it is not a good method of making bromine. If you add NaBr or KBr to conc. H2SO4, then most of the bromine will escape as HBr and only a small part as Br2, while at the same time SO2 is formed. So, basically, you get a mix of mostly HBr, with some Br2 and some SO2 in it. There is enough Br2 though to see a clearly visible orange/brown color in the gas-mix.

When this gas mix comes in contact with water, then the SO2 and Br2 react again, to give H2SO4 and HBr. The fact that SO2 is more volatile than Br2 may lead to escape of some SO2, while Br2 remains behind. So, in practice, you get a little left-over Br2 in your water, with larger amounts of HBr and some H2SO4.

Summarizing: A useless crap method of making Br2.

I suggest you to use the search engine, use Google and use site:sciencemadness.org as part of your search query to limit search results to sciencemadness.org.

bismuthate - 26-10-2013 at 13:48

I see how could work. However there are many a thread on this.
P.S. as deltaH said where would the other sulfur atom go? This could be an intesesting reaction to react dry HBr an SO2.
Edit Would this reaction Work with SO3 or 03 or other gaseous oxidisers (I believe it would) ?

[Edited on 26-10-2013 by bismuthate]

deltaH - 26-10-2013 at 13:54

Ah... interesting woelen, so you definitely make some Br2 though, is it that the extremely acidic conditions shift that sulfate reduction half reaction so much that it works? That's pretty impressive, a whole volt shift!

Now I'm curious to work out what the reduction potential of 98% H2SO4 is... and I understand why blogfast25 said that he's conc. H2SO4 was too oxidising in his attempt to produce Ti alum.

[Edited on 26-10-2013 by deltaH]

Cou - 26-10-2013 at 13:56

So what is a better way of making bromine? I remember reading a method that uses electrolysis, sodium bisulfate and sodium dichromate but I can't find it

bismuthate - 26-10-2013 at 13:58

Bubble chlorine through NaBr, or as I said before mix HCl, bleach and NaBr. There are a ton of videos on youtube U2U me or post here if you want one. The electrolysis will be relatively hard I believe.
Oh yeah by the way here is the video for the way you mentioned which was made by mrhomescientist, a member of SM
http://www.youtube.com/watch?v=NKjyM2AkZSY

[Edited on 26-10-2013 by bismuthate]

[Edited on 26-10-2013 by bismuthate]

Pyro - 26-10-2013 at 14:06

oops,
I'll edit it. I misplaced the 2. it should be 2H2SO4+Br2.
thanks

Random - 26-10-2013 at 14:12

Quote: Originally posted by deltaH

If I'm not mistaken, pyro here is SM's resident bromine making expert

So ask nicely...

@bismuthate... yeah don't you just hate it when that happens? I know I do!

[Edited on 26-10-2013 by deltaH]

You know alot about forum members for 1.5 month old account. Perhaps this account wasn't the first one?

Metacelsus - 26-10-2013 at 14:12

When I isolated bromine, I electrolyzed my sodium bromide until 1/6 of it was converted to sodium bromate, and then added sulfuric acid:

5 Br^- + BrO₃^- + 6 H⁺ -> 3 Br₂ + 3 H₂O

My yield from 103 g NaBr was 25 ml of bromine, which is near theoretical.

bismuthate - 26-10-2013 at 14:16

Random I don't recognize him so he may have just been watching, this is most likely his first. I did for a year before I signed up.
Cheddite Cheese how long did it take and how much did you use?

Pyro - 26-10-2013 at 14:18

http://www.youtube.com/watch?v=AL9ehxTaYRs
Br2 by KMnO4+NaBr+H2SO4 (I do it like this

http://www.youtube.com/watch?v=OB4MmPTOBxg
Br2 by NaBr soln. and Cl2

http://www.youtube.com/watch?v=6L7hIWZzWE8
Br2 by NaBr+H2SO4

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

Br2 by KBr+KBrO3+H2SO4

http://www.sciencemadness.org/talk/viewthread.php?tid=13104

SM's own writeup on making Br2. Written by Magpie
[Edited on 26-10-2013 by Pyro]

[Edited on 26-10-2013 by Pyro]

Metacelsus - 26-10-2013 at 14:29

The electrolysis took 12 hours (overnight). The distillation of the bromine from the acidified solution took about 45 minutes. I ampouled the bromine, but when I was flame sealing the (cheap) ampoule the glass cracked and some spilled on my hand. I was able to save most of the bromine, though, and the bromine burn I got has healed completely.

WGTR - 26-10-2013 at 14:52

Here was my experience:

For about 1mL of liquid bromine (think carefully if you want to isolate more of this
at one time):

Make a saturated solution of NaBr in about 200mL of ice cold water that is kept on
an ice bath.

With graphite electrodes, electrolyze the solution. Make sure that the bottom of
the anode is close to the bottom of the beaker. The cathode can be up near the
top of the solution.

As the solution is electrolyzed, a bromine-colored solution will run off the anode
and settle to the bottom. Don't disturb this layer as it forms.

The current needs to be adjusted to as high a level as possible without forming
oxygen bubbles on the anode. No gas bubbles should be formed on the anode.

Bromine is quite a bit soluble in NaBr solution (much less so in pure water), but as
this bromine-containing layer saturates, tiny bromine droplets will start flying off
the end of the anode, and collecting in a tiny puddle. Make sure that this little
puddle is close by to the tip of the anode (so the bromine doesn't dissolve so
much), but not directly touching it.

There is a limit to how much bromine you can get at one time with this solution, as
sodium hypobromite begins to form as the solution becomes significantly
alkaline. Once this happens, your anode starts to deteriorate.

After a sufficient amount of time (several hours), you should have enough product
to be able to pipette the bromine liquid from the small puddle at the bottom of the
beaker, and transfer it to a small container with pure water in it. As long as the
water is kept below the boiling point of bromine, the bromine's limited water
solubility will keep it sitting happily at the bottom for a considerable time (maybe
not long enough for permanent storage, but certainly long enough for you to use
it).

For extra credit, you can pipette the bromine-rich NaBr solution to a boiling flask,
and gently distill the extra bromine out of the solution. Dark bits of Br2 will start
coalescing in the condenser, and can be collected in cold water.

[Edited on 26-10-2013 by WGTR]

deltaH - 26-10-2013 at 15:14

random, I beleive it had something to do with the romanians...

Pyro - 26-10-2013 at 15:17

well, yes. but I have a history with Br2

In my mind it's the second coolest thing I have, the coolest being P4!

see: http://www.sciencemadness.org/talk/viewthread.php?tid=22645#...
that plante1999 so gentlemanly posted without my permission.

(jeez, makes me look incompetent

, just one fuck up after another, seems fate isn't on my side)

[Edited on 26-10-2013 by Pyro]

deltaH - 26-10-2013 at 15:26

Don't worry Pyro, we've all had our moments, I've had many worse lol

Pyro - 26-10-2013 at 15:37

how about an out of control P fire involving 1kg P and a near death?
http://www.sciencemadness.org/talk/viewthread.php?tid=23941#...

bismuthate - 26-10-2013 at 15:50

I accidentaly spilled lead acetate on my desk and dissolved my socks in acid last week. Everyone has their moments.

P.S. in another thread you said that there is still phosphoric acid in the air in your lab. How did it last that long?

Pyro - 26-10-2013 at 16:13

The breath stinging stayed around for a week or so. perhaps you mistook it for bromine vapor

How did you dissolve your socks???

bismuthate - 26-10-2013 at 16:18

They fell in a nitrating bath. It made NO2 and turned to a green chunky mixture.

deltaH - 26-10-2013 at 16:28

lol bismuthate classic!

Cou - 26-10-2013 at 21:33

Quote: Originally posted by Cheddite Cheese

The electrolysis took 12 hours (overnight). The distillation of the bromine from the acidified solution took about 45 minutes. I ampouled the bromine, but when I was flame sealing the (cheap) ampoule the glass cracked and some spilled on my hand. I was able to save most of the bromine, though, and the bromine burn I got has healed completely.

In the video posted above, it took almost 26 hours

unionised - 27-10-2013 at 01:57

Quote: Originally posted by Cheddite Cheese

I was able to save most of the bromine, though, and the bromine burn I got has healed completely.

Love the sense of priorities. :-)

MrHomeScientist - 28-10-2013 at 06:55

Man my videos are showing up all over SM today. My fame is growing

My electrolysis took 26 hours because that is how the math worked out to produce the optimum ratio of bromide to bromate. You could certainly run for less time, but you would get accordingly less product. When it must be electrolyzed for so much time regardless, why not run it to completion?

Quote:

I remember reading a method that uses electrolysis, sodium bisulfate and sodium dichromate but I can't find it

With a bare minimum of effort, you can find all that you seek through Google. Typing in words copied from your description, "bromine electrolysis sodium bisulfate," yields my video on this method as the first hit.

Quote:

I'm too lazy to use stochiometry

This is a terrible way to approach chemistry. There are some hobbies, like cooking, where exact measurements aren't completely necessary, but chemistry is not one of them. If you do not do your stoichiometry, very bad things can happen. You waste chemicals, lose products, and can cause dangerous runaways or unexpected side reactions. Having the skill and patience to do the math beforehand is absolutely essential here.
You also must understand how the reaction works before attempting it. What are the possible products? Does it need cooling/heating? Write out the balanced equation before you do anything, and see if your plan makes sense. Chemistry is a lot of fun and a great hobby, but can literally kill you if you do not respect it. If you really are "too lazy," put your chemicals away for a few years before you seriously hurt yourself.

Metacelsus - 28-10-2013 at 07:06

I electrolyzed for less time than you did, but at higher current. I calculated the total amount of charge I needed by Faraday's Law of Electrolysis, so I'm pretty sure I electrolyzed it for long enough.

MrHomeScientist - 28-10-2013 at 07:33

Of course - you can certainly change parameters around and get the same results as long as the math works out. In my comment I meant that if everything else was kept the same as my setup but run time was reduced, you'd obtain less bromine at the end. It's also detrimental to run it too long!

Cou - 28-10-2013 at 16:03

Quote: Originally posted by Cheddite Cheese

I electrolyzed for less time than you did, but at higher current. I calculated the total amount of charge I needed by Faraday's Law of Electrolysis, so I'm pretty sure I electrolyzed it for long enough.

Just made the solution with 100 grams of sodium bromide in 300 ml of water, and half a gram of sodium dichromate. I was going to do this with a 1 amp power supply for 40 hours, but I can't start because I only got 1 carbon electrode instead of 2 >_<

Also does the amount of electrode exposed to the solution matter? What if I only submerged a tiny amount of electrode, vs the whole thing? If it doesn't matter, I can just snap the one carbon electrode I have in two pieces, and use those

[Edited on 29-10-2013 by Cou]

WGTR - 28-10-2013 at 16:18

Quote: Originally posted by Cou

I can just snap the one carbon electrode I have in two pieces, and use those

[Edited on 29-10-2013 by Cou]

You might want to hold off snapping your precious carbon
electrode in two. The anode material is more important than
the cathode material, and you can probably use something else
for the cathode.

Metacelsus - 28-10-2013 at 16:32

The amount of electrode in contact with the solution does matter. You don't want to be operating at too high of a current density, or else you will get side reactions, like formation of oxygen, and excessive anode erosion. As for the electrodes, WGTR is right: you should use something else, like stainless steel, for your cathode. Personally, I used a MMO anode and titanium cathode, but I'm guessing you don't have those.

Cou - 28-10-2013 at 18:56

Well I already snapped my carbon electrode in two >:-( wonder if there is a place i can buy more, because elemental scientific takes forever to ship

ParadoxChem126 - 28-10-2013 at 20:58

For the carbon electrode:

http://www.youtube.com/watch?v=knc1lSupAwQ

woelen - 29-10-2013 at 09:47

Here is a write-up of the NaBr/NaHSO4 method. I have made this write-up a few years ago, with the goal of making bromine a more accessible chemical for many home chemists.

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

The hexavalent chromium, needed in the experiment, now also is not a problem anymore. Use some bleach and chromium sulfate or chrome alum (which both are available on eBay frequently and are not suspected and have no hazmat properties) to make a solution of hexavalent chromium, which can be added to the concentrated solution of NaBr as is, without the need to isolate the hexavalent chromium.

[Edited on 29-10-13 by woelen]

Cou - 29-10-2013 at 12:59

Quote: Originally posted by woelen

Here is a write-up of the NaBr/NaHSO4 method. I have made this write-up a few years ago, with the goal of making bromine a more accessible chemical for many home chemists.

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

The hexavalent chromium, needed in the experiment, now also is not a problem anymore. Use some bleach and chromium sulfate or chrome alum (which both are available on eBay frequently and are not suspected and have no hazmat properties) to make a solution of hexavalent chromium, which can be added to the concentrated solution of NaBr as is, without the need to isolate the hexavalent chromium.

[Edited on 29-10-13 by woelen]

YES, that's the website I was looking for. Just curious, what happens to the hexavalent chromium after you get the bromine? And in the part where the bromine pools in the bottom, what is all the foamy stuff above it?

woelen - 29-10-2013 at 13:12

The hexavalent chromium simply remains in the aqueous layer. It might be that some of it is converted to trivalent chromium. It only plays a role during the electrolysis, it largely prevents the back-reduction of bromate to bromide.

The 'foamy stuff' above the bromine is not really foam. It is an aqueous layer. It looks foamy, due to small bubbles of air, sticking to the glass under the liquid, combined with the very bright light of the flash unit from my camera. The lighting of that picture is sub-optimal, it could have been better.