(Piano music)
Vanadium, element number 23,
the third of the so-called "transition metals,"
so it lies between titanium and chromium
in the Periodic Table.
I don't know a huge amount about the chemistry
of vanadium. I've never actually seen vanadium metal,
so let's have a look at it.
It's in a really quite historic box.
It's wire; it's not easy to open.
And you can see there's a coil
of fairly black-ish coloured wire.
There are several things that interest me:
first of all that you can make wire as thin as that,
and secondly, that it doesn't look very shiny,
possibly it's got an oxide layer on the surface.
I've been given another sample: of vanadium powder,
but vanadium powder can catch fire quite easily,
and so I don't really want to take it out
because we might have a fire here on the table
in my office!
Vanadium metal is quite light,
and it is used in a variety of alloys.
It is also like many of the transition metals,
you can have different so-called "oxidation states"
with different numbers of electrons
around the vanadium atom.
Now, there's a really nice demonstration
which you should watch carefully
because it's what our first-year students do.
So if you come to this university, and several others,
if you know this,
you'll get better marks on your Practical!
Darren, my colleague, really enjoys doing this reaction.
[Dr. Darren Walsh] Vanadium five.
It's a yellow solution of ammonium metavanadate.
As you can see, it's a nice yellow colour,
and one of the really nice things about
the various oxidation states of vanadium
is that they're different colours.
So what we have here is we have a metal amalgam.
Now this is mercury, as you can see
we have mercury with some zinc in it.
The really nice thing about this amalgam is
that we can convince some electrons to jump
from this metal amalgam onto some other species.
So remember: vanadium five,
and I'm gonna put in here a glug of vanadium five.
It's not a scientific quantity, that's... that's,
that's uh... A glug is... It's a good glug.
The vanadium solution is sitting on top
of the mercury-zinc amalgam,
and hopefully, what I'm a-gonna do is by shaking it up
I'm gonna convince some of the electrons in the metal
to jump onto the vanadium species,
changing the oxidation state of the vanadium.
As I do it, hopefully we'll see a colour change.
Can you see the yellow?
[Brady Haran] Yeah I can, yeah.
[Dr. Walsh] Alright, so let's see...
So now: a nice blue colour, right?
And the blue colour, I happen to know, is vanadium four.
Alright? So each of the vanadium species
has gained one electron, changing its oxidation state,
or it has been "reduced."
So if I shake it a bit more, I'm gonna see
can we convince more of the metal to give up electrons.
Alright? So I think we're looking for
a nice green colour,
and you can see it's got a kind of a green colour there,
Can you see that as green?
We've gone from vanadium five, to four, to three.
OK, so now I need to shake it up
a lot to see can I convince another electron to go
and access vanadium two.
So, let's see. And this is... 'cos mercury is so heavy!
This is slightly hard work.
So there we go!
Purple.
Vanadium two, so we've gone vanadium 5, 4, 3, 2.
Four different oxidation states of vanadium,
resulting in the really nice purple
vanadium two species.
And then what would happen is,
if we put that on the bench
and left the lid off,
oxygen can obviously...the air can get into the container,
and what will happen is we will oxidize
this solution again. So if we waited for long enough,
we would see the colours go in reverse.
[Sir Martyn] You can find vanadium in nature.
There are mushrooms:
the sort of red ones with white spots
that faeries and elves sit on in faery tales
(I never know the difference
between mushrooms and toadstools...
the things that grow in forests),
and in this mushroom, or maybe toadstool,
nobody's quite sure
why there are vanadium compounds.
One idea is they just may be a poison
to discourage people from eating it --
or not people, but animals, slugs, worms.
The other theory is that the vanadium
may react with hydrogen peroxide,
which can sometimes be formed
in biochemical processes, and which would otherwise
attack more important molecules
to the life of the mushroom. Or toadstool.
But I think it's really quite interesting
that a mushroom, or a toadstool,
can do good vanadium chemistry.
...match on a stick to blow up balloons with hydrogen.
And the thing that's always puzzled me
is that when they blow up,
the flame has a reddish colour,
and it's well known that hydrogen, when it burns,
for example in a Bunson burner or something like that,
gives an almost colourless flame.