NaBr to Br

How difficult is it to change NaBr back to Br? What easy ways can this be done?


Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

It's real easy; there are

It's real easy; there are three common methods.

1) Electrolysis

Dissolve the NaBr in water and apply an electric current; the negatively charged Br- ions will migrate to the anode; then Br2 can be collected in a tube over the anode as gas if the temperature is high enough. The tube can be routed to a container in an ice bath and the Br(g) will condense into reddish brown Br(l). When all of the Br is electrolyzed, the solute will be NaOH. Be careful, the cathode will produce hydrogen, which will spark if you are stupid enough to smoke around it; you'll just get emphysema or lung cancer if you are stupid enough to smoke elsewhere.

2) Displacement

Dissolve NaBr in water, keep it warm and pass Cl2 gas through the solution. Br2 will come out as a gas that can be collected like distillation in a container kept in an ice bath. You can make the Cl2 at home simply by adding a little spare NaHSO4 to liquid chlorine bleach and directing the evolved gas into the NaBr solution. I believe that historically this was the way that Br and I were first identified.

3) Oxidation

You can also heat NaBr in a retort with H2SO4 and a powerful oxidant like MnO2 and distill the Br(g) that way, but it isn't much fun.

Do remember that Br(g) and Cl(g) are not good for the lungs, so plenty of ventilation is required.

While those above methods

While those above methods would work, they are far from ideal. Perhaps the easiest route to elemental, diatomic bromine is wet chem. oxidation as electrolysis of NaBr (also an oxidation!) is not exactly the most efficient process because there are competing reactions occurring. Anyone who has actually done the electrolysis of NaBr can comment that little to no bromine is formed. Most likely you will get bromate from bromide or perhaps bromine water rather than the element itself (depends on cell temperature).

Displacement sounds nice but it doesn't work quite as well either because 1.) bromine is quite soluble in water forming quite a few aqueous species, and 2.) chlorine reacts with bromine to form bromine chlorides.

Oxidation is probably one's best bet for elemental bromine. The best method which is nigh on quantitative for yield is to use potassium bromate as the oxidiser. Potassium bromate is made simply from the electrolysis of KBr with a platinum or carbon anode (titanium, even platinised doesn't work!). This bromate is reacted at room temperature with conc. HBr to give elemental bromine which is either sep-funneled off or pipetted off from the bottom. 80% yields can be realised without distillation, to get the rest, one must distill the bromine water and then shake the product with conc. sulfuric to rid it of water.

Alternatively, one may use any alkali chlorate, alkali bromide, and any common proton source as follows:

NaClO[sub]3[/sub] + 6NaBr + 6 HCl --> 7 NaCl + 3Br[sub]2[/sub] + 3H[sub]2[/sub]O

which will also give high yields of bromine. Of course chlorate can be replaced with bromate, just adjust the equation accordingly. Hope this sets the record straight!

For displacement you heat

For displacement you heat the evolved Br(g) and pass it through CaCl to absorb the H2O and then run the Br(g) through a Leibig condenser to get Br(l). Most of these things can be found by consulting old chem books and lab manuals from the times when the students were actually supposed to work with the substances rather than read gauges.

WebElements: the periodic table on the WWW []

Copyright 1993-20010 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.