making potassium bromide

[hermanntrude]

OK so today I tried a new demo and i'm very excited.

 

Before I start I should remind everyone that this cannot be attempted outside of a proper chemistry laboratory. Bromine is extremely hazardous and hard to safely dispose of and handle and the same is true of potassium.

 

Anyway, what I did was this:

 

I took a long piece of metal (steel, i think), and bent the end downwards by 90°, so that the end part was just long enough to reach the bottom of a large beaker. To the end I attached a piece of copper wire. Into the large beaker I placed a small beaker with enough bromine in it to cover the bottom. To the top of the bent part of the metal stick I attached a DVD so that when the stick was fully inserted into the beaker, the DVD would cover the opening at the top of the beaker.

 

I then attached a very small (perhaps 2-3mm diameter) piece of potassium metal (washed in hexane and dried in air) to the wire at the tip of the metal stick. I then placed an explosion guard over the front of the beaker and lowered the sash of the fume hood as far as possible. Then I lowered the potassium into the bromine.

 

A small explosion ensued and copious quantities of white smoke floated gently away into the fume hood.

 

it was awesome.

 

Video to follow at a later date.

[John Cuthber]

I look forward to the video.

However, just in case anyone ever looks up this thread because they want some KBr and they have some bromine, here's a less "exciting" way to do it. (I have a rough idea how likely that is, but this post didn't cost much)

 

Pass bromine over heated iron filings to produce a mixture of iron bromides. (or dissolve the Br2 in a suitable solvent and react it with iron.) Leach the Fe bromides into water and add potassium hydroxide or carbonate until all the iron is precipitated.

filter off the Fe oxide/hydroxide/carbonate then evaporate down the solution to get KBr.

[hermanntrude]

nice method. Of course, KBr is dirt cheap anyway :0)