So today we’re going to look at bromine. So this is bromine, it’s a small
sample, about 2 or 3 grammes.
Bromine is a red liquid. There are not many elements that are actually
liquid: caesium, mercury, gallium and bromine. It’s this beautiful red
colour and it has an unpleasant smell. Bromine comes from the Greek
word bromos which means stench, a really horrible smell.
In fact this bromine probably comes from near where I did my degree
because in Europe, the second, well the largest producer of bromine in
Europe is the Octale Company which is based on Amlwch on Anglesey
which is where I went last weekend. So it’s a nice sample. We’re going to
get it out of this bottle now because it’s sealed in because it’s obviously
very, very volatile as a liquid and we’re going to cut the glass, get it out
and look at its chemistry. Thanks Neil.
Bromine is also quite a common element in the world. It is found in sea
water as bromide, it’s also found particularly in the Dead Sea between
Israel and Jordan where there are very concentrated solutions of
bromide. So you can make bromine just by bubbling chlorine into a
solution of bromide like Dead Sea water and the chlorine displaces the
bromine and forms chloride and the bromine just comes out as red
fumes which you can catch.
So Neil’s now using a glass knife to open the ampoule and he’s going to
pour the liquid bromine into this small evaporating dish inside our fume
hood. Now instantly you can see the vapour of the bromine coming off.
You see all those really nice orange fumes which are coming off from the
liquid and then they’re being drawn away by our fume hood.
Bromine has a number of uses, it is particularly used in plastics as an
additive to try and make them less flammable. If you’re watching your
videos on a screen which has a plastic surround almost certainly that
surround will contain bromine to make it less flammable.
Bromine itself is strongly oxidising so we thought we’d do an oxidation
reaction today. And that reaction is to take another element and here we
have aluminium, simple aluminium foil, like you wrap your dinner in, and
we’re now going to put some small amounts of aluminium foil into the
bromine liquid. So we put it in and it generally takes a few moments for
this reaction to start but as I said, the aluminium is strongly oxidising. It
oxidises and generates aluminium tribromide. Which is a beautiful nice
material but it’s a strongly exothermic reaction. So let’s see what
happens. This may initiate.
It is also an unusual element because elements have different isotopes
these are the same form of the element but with different numbers of
neutrons in the atoms so they weigh different amounts. Usually you get
one isotope that is very common and another one that is only a small
amount. Bromine is unusual because it has two isotopes 79 and 81 which
have almost equal quantities in nature so that they have approximately
51% of one and 49% of the other which is really quite unusual.
So here we see the exothermic oxidation and formation of aluminium
tribromide. So the reaction is strongly exothermic which
means it gives out energy and that energy then evaporates
off excess bromine which you can see coming off as a vapour. A wonderful
exothermic reaction: very, very fast, very, very rapid forming
aluminium tribromide.
Bromine is quite dangerous but it is less dangerous than chlorine because
it’s a liquid at room temperature. Chlorine is a gas so if you let out
chlorine it disperses everywhere. With bromine it is a heavy gas which
can disperse rather more slowly.
So now as the reaction cools down we can see that the volume of
bromine is significantly reduced.
Reacts with water quite well.