Sciencemadness Discussion Board - Freezing Bromine: video

Freezing Bromine: video

metalresearcher - 8-12-2012 at 03:22

I tried to freeze bromine using table salt and snow outdoors in winter temperatures.

Here the video:

<iframe sandbox width="640" height="360" src="http://www.youtube.com/embed/ssM_jI4iSmk" frameborder="0" allowfullscreen></iframe>

smaerd - 8-12-2012 at 06:08

Pretty cool little demonstration. Working with frozen bromine sounds a lot better then the stanky liquid. Does that reagent bottle store Br2 without too much of an issue?

Manifest - 8-12-2012 at 07:53

Nice video, it would be alot easier to store it like that.

May I ask, what country are you from?

metalresearcher - 8-12-2012 at 08:12

From Holland where it is very cold now.

Endimion17 - 8-12-2012 at 18:32

Interesting, but far from being correct. You've got a mixture of wet bromine and water, not "bromine".
After the freezing, you get a slush of water ice contaminated with bromine, bromine hydrate, and solid bromine contaminated with water. That's where the first error comes to mind.

Also, you can't expect to get a proper reading using a pyrometer. Snow is incredibly effective as a thermal insulator.
Pyrometers are used for measuring hot gasses and hot surfaces, and if used for measuring temperature of bulk matter, they're employed when you've got a molten mass of metal or hot water, both quite effective in heat transfer.

You'd get a far more accurate reading if you just stucked a cheap digital cooking thermometer inside.

neptunium - 8-12-2012 at 18:52

i kept Br2 in a regular freezer for months...without much leakage at all ...been doing that for years

metalresearcher - 9-12-2012 at 01:06

Quote:

[quote=268131&tid=22640&author=Endimion17]Interesting, but far from being correct. You've got a mixture of wet bromine and water, not "bromine".
After the freezing, you get a slush of water ice contaminated with bromine, bromine hydrate, and solid bromine contaminated with water. That's where the first error comes to mind.

How can I separate the water layer from the Br2 ? Using a pipet and holding it carefully in the water layer still sucks some bromine with the water.

Quote:

Also, you can't expect to get a proper reading using a pyrometer. Snow is incredibly effective as a thermal insulator.
Pyrometers are used for measuring hot gasses and hot surfaces, and if used for measuring temperature of bulk matter, they're employed when you've got a molten mass of metal or hot water, both quite effective in heat transfer.

You'd get a far more accurate reading if you just stucked a cheap digital cooking thermometer inside.

That's why I used a mercury thermometer as well to measure the temperature *inside* the snow / salt mass. This one also recorded -20ºC as the stem was completely empty (lower limit -19ºC).
But I tested the pyrometer extensively before at freezing temperatures and the readings match +/- 2ºC with the readings of other thermometers.
And in this case I did not point the device to the snow but to the cold salty slush which is a much poorer insulator which favors temperature readings.

[Edited on 2012-12-9 by metalresearcher]

neptunium - 9-12-2012 at 05:26

separatory funnel and a good fume hood!...then put the bromine back in the funnel with conc sulfuric acid shake and vent often ...you already know it will get hot...get ready to run just in case!

always small amount so you dont get a lung bleed!

good luck!

metalresearcher - 10-12-2012 at 01:25

Quote: Originally posted by Np

then put the bromine back in the funnel with conc sulfuric acid shake and vent often ...you already know it will get hot...get ready to run just in case!

Thanks, but is CaCl2 not safer to remove water from the bromine ? And does Br2 not react with H2SO4 ?

Endimion17 - 10-12-2012 at 04:55

Quote: Originally posted by metalresearcher

How can I separate the water layer from the Br2 ? Using a pipet and holding it carefully in the water layer still sucks some bromine with the water.

Make a narrow pipette, cool both vessels in ice bath and start transfering, carefully. It's possible, but requires a steady hand and practice. Stray bubbles of water will merge together overnight and can be removed by the same pipette.
You'll end up with wet bromine. Depending on your needs, you can use various drying methods. Extraction of water using concentrated sulphuric acid, distillation and pulling bromine through various columns (the latter, when used as the last in a series of steps, gives extremely pure bromine) are common methods.

If you don't need pure bromine, don't do it. Purification is incredibly dangerous if not done in suitable apparatus (your glassware, at least the one I saw is completely ineffective for it) with powerful ventilation and cooling. It's something only pretty experienced experimenters should do.
Really, you can end up dead in hospital. Death from oedema can be delayed.

Quote:

That's why I used a mercury thermometer as well to measure the temperature *inside* the snow / salt mass. This one also recorded -20ºC as the stem was completely empty (lower limit -19ºC).But I tested the pyrometer extensively before at freezing temperatures and the readings match +/- 2ºC with the readings of other thermometers. And in this case I did not point the device to the snow but to the cold salty slush which is a much poorer insulator which favors temperature readings.

As long as you're sure the stuff is calibrated...
You'd be surprised how precise these things can be below 50 °C. Their precision is usually +/- 1 °C above 100 °C, but around water freezing point, they work great.

[Edited on 10-12-2012 by Endimion17]

woelen - 10-12-2012 at 06:31

Think the other way around. Pipette the bromine away from the lower layer instead of the water. I have done that several times before. I pipetted away the bromine from under the water layer and transferred this to another vial, which contained a few ml of concentrated H2SO4. I let the bromine run out of the pipette while the tip of the pipette is under the sulphuric acid. In this way, you can suck up all bromine, the blob of bromine simply becomes smaller and smaller while sucking away the bromine.
If you accidently suck up a little water as well, then that is not a real issue. That drop of water simply is absorbed by the H2SO4.

In this way you get perfectly dry bromine under a layer of H2SO4. Bromine does not mix with H2SO4. Some bromine (slowly) dissolves in H2SO4, the other way around, H2SO4 is practically insoluble in bromine. I tested this by taking a drop of the bromine and allowing this to evaporate. No visible film of H2SO4 remains behind.

smaerd - 10-12-2012 at 07:13

Woelen does that mean that bromine could be stored under H2SO4 to reduce it's volatile nature?

woelen - 10-12-2012 at 07:35

It can be stored under H2SO4, and indeed in some sense reduces its volatile nature. In the long run there will be the same amount of bromine vapor above the H2SO4-layer as when no H2SO4 is present, but when the bottle is opened and this vapor is gone, then release of new vapor from the H2SO4 is much slower than release of vapor from uncovered Br2.

Endimion17 - 10-12-2012 at 08:55

Quote: Originally posted by woelen

Think the other way around. Pipette the bromine away from the lower layer instead of the water. I have done that several times before. I pipetted away the bromine from under the water layer and transferred this to another vial, which contained a few ml of concentrated H2SO4. I let the bromine run out of the pipette while the tip of the pipette is under the sulphuric acid. In this way, you can suck up all bromine, the blob of bromine simply becomes smaller and smaller while sucking away the bromine.
If you accidently suck up a little water as well, then that is not a real issue. That drop of water simply is absorbed by the H2SO4.

In this way you get perfectly dry bromine under a layer of H2SO4. Bromine does not mix with H2SO4. Some bromine (slowly) dissolves in H2SO4, the other way around, H2SO4 is practically insoluble in bromine. I tested this by taking a drop of the bromine and allowing this to evaporate. No visible film of H2SO4 remains behind.

Well that's the general idea, to suck the bromine, not the water. I thought it was obvious.

However, you won't get perfectly dry bromine using your method. If it was enough, this (Armarego, Chai, Purification of Laboratory Chemicals) wouldn't exist:

Quote:

Refluxed with solid KBr and distd, dried by shaking with an equal volume of conc H2SO4, then distd. The H2SO4 treatment can be replaced by direct distn from BaO or P2O5. A more extensive purification [Hildenbrand et al. J Am Chem Suc 80 4129 19581 is to reflux about 1L of bromine for 1h with a mixture of 16g of CrO3 in 200mL of conc H2SO4 (to remove organic material). The bromine is distd into a clean, dry, glass-stoppered bottle, and chlorine is removed by dissolving ca 25g of freshly fused CsBr in 500mL of the bromine and standing overnight. To remove HBr and water, the bromine was then distd back and forth through a train containing alternate tubes of MgO and P2O5.

One shake with equal volume of conc. acid can be replaced with two shakes using half the amount.
Distillation is essential, and MgO/P2O5 tubes are used for stubborn traces.

Whatever is done, it's very dangerous. In most cases, it's better just to buy the damn thing.

metalresearcher - 10-12-2012 at 10:39

And does CaCl2 work instead of H2SO4 ? I have both but I think CaCl2 is safer.

Endimion17 - 10-12-2012 at 15:10

Quote: Originally posted by metalresearcher

And does CaCl2 work instead of H2SO4 ? I have both but I think CaCl2 is safer.

Surface area is larger with two liquids. It's more effective and it's easier to work with using a separatory funnel and common organic chemistry lab practice.
Calcium chloride can create a gunk. I hate when that happens.

If you're going to use bromine for demonstration experiments showing its reactivity, just remove it using a pipette.

Lambda-Eyde - 10-12-2012 at 15:18

If you used calcium chloride you'd have to filter the bromine, an operation known to promote the sudden evacuation of chemists' bowels...

Endimion17 - 10-12-2012 at 15:32

Quote: Originally posted by Lambda-Eyde

If you used calcium chloride you'd have to filter the bromine, an operation known to promote the sudden evacuation of chemists' bowels...

It would float.

bromine 3.10 g/cm3

calcium chloride
2.15 g/cm3 (anhydrous)
1.835 g/cm3 (dihydrate)
1.83 g/cm3 (tetrahydrate)
1.71 g/cm3 (hexahydrate)

Gunk would have even lower overall density but stubborn emulsion could form easily upon shaking/stirring. Imagine that. Bromine and calcium chloride+water emulsion. Well fuck that.

I say - buy the damn thing if you can.

woelen - 11-12-2012 at 02:18

Quote: Originally posted by Endimion17

Quote: Originally posted by woelen

Well that's the general idea, to suck the bromine, not the water. I thought it was obvious.

However, you won't get perfectly dry bromine using your method. If it was enough, this (Armarego, Chai, Purification of Laboratory Chemicals) wouldn't exist:

Quote:

What you write about is quite extreme. If you want VERY pure bromine, then of course you need distillation and drying with strong drying agents or doing multiple drying sessions. But for most practical purposes a single shake with conc. H2SO4 or storing under conc. H2SO4 is good enough. I'm quite sure that general lab grade Br2 is not better or more pure than your home-made stuff, dried with H2SO4 and produced in an environment without chloride/chlorine. The material I made is more than good enough for synthesis purposes, demonstration purposes and making nice element samples, which nicely run off glass and do not wet the glass.

At the end of the following page you can see my home-made ampoules of Br2, using Br2 which I made at home as well.

http://woelen.homescience.net/science/chem/compounds/bromine...

Especially the shaking of the ampoules nicely shows that the Br2 does not stick to glass. This is made by drying under H2SO4.

DJF90 - 11-12-2012 at 03:56

Nice video Woelen, it was interesting to see. Whats your preferred method for making bromine from aqueous solutions, such that recovery of bromine by pipetting is viable (and in good yield?)?

woelen - 11-12-2012 at 04:12

I prefer the electrolytic method of electrolysing a strong solution of NaBr, such that appr. 1/6 of the bromide is converted to bromate and then adding an acid to the solution. No need to isolate bromate, just keep on electrolysing for the right amount of time.

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

This uses only OTC chemicals, except some chromate. Chromate can be made from chrome alum and bleach or chromium sulfate and bleach. Chrome alum and chromium sulfate are easy to obtain, frequently available on eBay. No need to isolate the chromate, just add a tiny amount of the chromate solution to the concentrated bromide solution. No problem if there is a small quantity of excess bleach or if there is slightly too little bleach, not critical at all.

Of course, you can substitute pH minus with H2SO4, but I liked to use OTC chemicals only.

DJF90 - 14-12-2012 at 22:44

So one thing that has suprised me is that noone seems to have mentioned the lachrymatory effects of bromine, though I found out first hand over the past hour or two, eyes continuously watering as I prepared and isolated it using a method related to Woelen's (NaBr + NaBrO3 + NaHSO4). It also made my nose rather runny, which was also unpleasant. It probably would have been nicer to run the reaction in a distillation setup, rather than a beaker covered with a RBF. Pipetting off the lower bromine layer took time (whilst crying) and then as I was using the Br2 crudely as a solution in DCM for a reaction, I figured I'd give an extraction with DCM a go, though this did not seem as efficient as I had imagined (aqueous layer was still strongly red-brown).

But yea, if you're doing this you might want to do it outdoors or in a fumehood. I found a half-face gas mask was of some comfort, but it still did not protect me from the earlier mentioned effects.

Endimion17 - 15-12-2012 at 00:52

Quote: Originally posted by DJF90

So one thing that has suprised me is that noone seems to have mentioned the lachrymatory effects of bromine, though I found out first hand over the past hour or two, eyes continuously watering as I prepared and isolated it using a method related to Woelen's (NaBr + NaBrO3 + NaHSO4). It also made my nose rather runny, which was also unpleasant. It probably would have been nicer to run the reaction in a distillation setup, rather than a beaker covered with a RBF. Pipetting off the lower bromine layer took time (whilst crying) and then as I was using the Br2 crudely as a solution in DCM for a reaction, I figured I'd give an extraction with DCM a go, though this did not seem as efficient as I had imagined (aqueous layer was still strongly red-brown).

But yea, if you're doing this you might want to do it outdoors or in a fumehood. I found a half-face gas mask was of some comfort, but it still did not protect me from the earlier mentioned effects.

I think those effects were mentioned few times. All halogens are quite powerful lachrymatory agents, but they need time to act. I once had this accident where a clearly visible cloud enveloped my face when a sudden change of air current occured (windy day, not enough exhaust power, wind overpressure in the system). I could sense the warm feeling halogen vapours are known for when oxydizing tissues (chlorine is way worse) so I immediatelly stopped breathing, stoppered the flask and ran like hell to reach water cause I knew I had like half a minute before I lose ability to open my eyelids. The pain was incredible and lasted half an hour despite copious flushing with water.

The important thing is that lachrymatory effects require air concentrations so high that they crossed the limit of being acutely poisonous via inhalation. If your eyes are burning up while working with bromine, you're obviously doing it wrong. You're in a great deal of danger and need to immediately cease your work and get fresh air.

Runny nose effect has two stages. The first one is sudden. The mucosa swells up and starts pushing water over cell membranes to wash out the irritant. The second one comes the day after (few days at most) if the exposure was higher, and is actually a viral infection of upper respiratory system. Bromine destroys the mucosa and destroys our defense cells that wander around and represent the first line of defense of our immune system. Viruses are just everywhere, so they attack first and you get a viral infection.

While this bromine thing seems like fun to amateurs, most of people here don't understand how dangerous its vapors are. Yes, it's less oxidizing than chlorine, but it's way more dense and the net effect is similar. Working unprepared with this is like going to WW1 while Haber is mounting his gas cyllinders on a nearby hill.

If one doesn't have a proper equipment (fully closed glass apparatus, ice cold coolant, strong exhaust system), one shouldn't perform this except as a demonstration experiment on a micro scale.

When pipetting this nasty liquid it is important to remember its fumes are heavy, but also that gas diffuses. Any manipulation which exposes bromine to atmosphere should be done next to a strong ventilation system previously tested for turbulence using smoke or perfume. You need a neat, laminar flow.

Bear in mind that quantities as small as 1 ml dropped on a floor of a tightly closed mid-sized room will probably kill by pulmonary oedema, given enough time is spent inside. Talking about a true Saw scenario...

[Edited on 15-12-2012 by Endimion17]