So now you can see the reactionís really going and itís really exothermic,
weíre forming aluminium triiodide, and the exotherm is actually heating
and starting to sublime off the excess iodine which you can see coming
off as this really nice purple plume.
Iodine is this beautifully-coloured element. It has this beautiful purple
colour. If you put it in solution, the colour of the solution varies
depending what you dissolve it in. If you dissolve it in water, itís a sort-of
dirty brown colour. If you dissolve it in an organic material like
chloroform or carbon tetrachloride it is a beautiful purple colour.
Iodine is halide, a halogen element from the far right-hand side of the
periodic table and it's strongly oxidising in nature. Likes to nick electrons
off other atoms, so what weíre going to do is we are going to do a
reaction with iodine, and today weíve ground some iodine. So itís
normally found from chemical suppliers as really nice large crystals. But
what we want to do as a reaction with it, well we need to make sure that
the surface area of the iodine is really, really large so that all of it can
react very very quickly with the other component.
Iodine also occurs quite widely in nature and is absolutely essential to
life. If you donít have iodine, your thyroid gland, which is a small gland
that controls development of all sorts of things in your body, doesnít
operate properly. Nowadays, iodide is added to table salt in countries like
the UK and most other developed countries so nearly everybody has
enough iodine. In the old days iodine had to be got from the
environment and usually from the spray from the sea that was blown
across the land, and so in Nottingham, which is really near the centre of
England a long way from the sea, or relatively long way from the sea,
there were serious illnesses caused by people not having enough iodine.
So-called goiter, which caused a swelling, the thyroid gland gets bigger,
and this used to be called Derbyshire neck this unpleasant illness,
because it happened in this area of Nottingham and Derbyshire.
So what weíre going to do is that we are going to mix it now with
another element and that element is aluminium. So aluminium has
electrons to give away. Iodineís gonna nab ëem. Going to see some
oxidation chemistry in the formation of a new compound, which is
aluminium triiodide. Itís a really nice chemical reaction. But the way that
we do it is that we mix the two together and we have to add water which
acts a bit like solvent and also the oxygen in the water activates the
iodine so that it becomes more strongly oxidising and then hopefully weíll
see the new reaction. So Iím going to just put some out into this small
vessel.
You can see this development effect of iodine really well that if you had
tadpoles, baby frogs, they donít develop their legs and turn into frogs
unless there is iodine in the water.
The other component in this reaction is aluminium, ok; and weíre using
very, very finely powdered aluminium. Not foil or not a rather large
lump. This has been especially powdered for us, so again it has a very,
very high surface area.
One of my favourite chemical equations is ëtadpoles plus iodine goes to
frogsí. So you can see the aluminium and the iodine mixed within this
solid mixture. Now still, these two components, these two elements they
are still held away from one another they canít react. So what we need
to do is add a small amount of water, which actually acts like a solvent
but actually activates the iodine and then weíll wait and see what
happens with the chemical reaction.
Iodine can be used as a disinfectant, in fact chlorine can be as well, but
solution of iodine is often used when people have cuts. So if you cut
yourself, fortunately I havenít any cuts at the moment, you can paint on
iodine and because of its rather red colour it made cuts often look much
worse. Children would come home from school and their whole hand
would be red and this would cause some excitement at home but it is
quite an effective antiseptic.
Water: just take a small amount and add it to the reaction. So you can
see itís starting to go now the chemical reaction because we are seeing
the excess iodine subliming in the form of a vapour. Now if we go in
close we can hear it fizzing because this is actually an oxidation reaction
and the formation of the new aluminium triiodide. Now Iím going to just
mix this slightly to try and increase the rate of the chemical reaction
slightly. So now you can see the reactionís really going and itís really
exothermic, weíre forming aluminium triiodide, and the exotherm is
actually heating and starting to sublime off the excess iodine which you
can see coming off as this really nice purple plume. Now deep inside the
reaction now you can see the exothermic or the energy coming out and
starting to cause a flame. Really, really nice, really rapid chemical
reaction: really beautiful. So weíre forming aluminium triiodide here
which again is a very, very delicate compound; quite reactive in itself.
So you can see now the really nice new crystalline material. So, sadly,
weíve managed to stain Stigís fume cupboard. All of this really nice
iodine forming a very fine layer across this fume cupboard.
What do you think about that?
Looks like a thorough cleaning job coming to be honest.