When Chemists Attack

[This is an update of an earlier post on this blog.  This version includes streaming video]

Let’s say you don’t want to do the thermite reaction, but you still want to see some flashy chemistry. The reaction between aluminum and bromine might fit the bill.

2Al(s) + 3Br₂(l) –> 2AlBr₃(s)

It’s a very simple-looking reaction – a little electron transfer from aluminum to bromine.  Like lots of these reactions, it’s exothermic.  Exothermic enough to put on an impressive show.

Enough heat is generated by the reaction to vaporize some of the unreacted bromine – throwing off orange smoke.  On top of that, the aluminum gets hot enough to melt and spark.  For obvious reasons, this reaction should only be done where you’ve got very good ventilation. I used my hood for these pictures and this video.

Here’s a still image of the reaction vessel containing only liquid bromine and its vapor.

Bromine is the dark red liquid at the bottom. Bromine is quite volatile, and you can see orange bromine vapor in the top of the beaker.

About ten seconds after adding some torn aluminum foil, things look more like this.

A little later …

And then …

… but you didn’t read all this way for still pictures, did you?  How about a video?

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After the reaction’s over, you’ll want to buy a new beaker.  The melted aluminum foil fuses with the bottom of the beaker.  (The sand bath is there to catch anything that gets through the bottom of the beaker when it breaks!)

So where’s the aluminum bromide?  Some of it has stuck to the sides of the beaker.

Aluminum bromide formed will react with water, causing the release of acidic hydrogen bromide vapors, so you need to be careful disposing of the product! That reaction is also very exothermic, so touching the product or adding water to it is not recommended. Leave it out long enough, though, and it will absorb water from the air on its own.

Ain’t chemistry neat?

Disclaimer: Do not try this reaction at home. In fact, do not try this reaction at all! You were warned.