between iron 26 and nickel 28,

and like most elements, it's really quite interesting

It is a catalyst

It can be used in magnets

It is important in the batteries that we have in all our modern electronic equipments and

Above all it is associated with the color blue.

The element or its compounds has been known for a long time because it's been used for coloring glass.

I found in my cupboard at home quite a nice glass jar which

everybody has told me is a 19th century

Christmas tree light with a candle in it though i'm sure some viewers will tell me it's something more boring

But i still think it's a Christmas tree light and you can see it has got this glorious, blue color.

Brady - "Did you buy it in the 19th century?"

I can't remember when I bought it but it was a long time ago. They add a small amount of cobalt

Into the melt when they're making the glass and so you get isolated

Ions of cobalt, which have this nice blue color. Cobalt itself is a

shiny metal if it's polished and

It's relatively, dense. It's quite heavy to hold. It's used principally in alloys with other

Metals it used to be used a lot in making magnets though now

You can get more powerful magnets using rare earths

Because cobalt is a so-called transition metal

The ions of cobalt say cobalt 2+, that's cobalt with two electrons removed

it's usually not naked, it will be

coordinated by other compounds

For example if you, make it using water

You get six water molecules round the cobalt,

so here you can see cobalt in the middle with six water molecules around it.

Now you might ask, how can you form so many bonds,

and the answer is that the interaction is partly electrostatic.

The negative oxygen interacting with the positive cobalt.

If you heat cobalt chloride, which is beautiful red colored crystals to high temperature,

you can drive off the water and make a sort of purplish powder.

We found a lovely really old sample of anhydrous (without water), cobalt chloride

in a bottle that still sealed up with its original wrapping.

We felt we really didn't have the heart to destroy this historic sample to destroy the wrapping, so you'll have to look at it through the glass.

We had another sample of anhydrous cobalt chloride,

where the bottle had split so air and water could get in and you can see it goes back to the pinkish color

So we've got two demonstrations for you the first one is to demonstrate

how in solution you can remove the water and substitute it with chloride ions,

by using concentrated hydrochloric acid.

We were so excited to do this that the first time, we didn't do it very, well

We had a test tube of cobalt chloride solution

Nice the pinkish color, and try dropping in concentrated hydrochloric acid

but although you could see some changes of color,

the concentration of the acid was not enough.

So, we reversed it

and dropped the pink solution into the colorless hydrochloric acid

so now we had a whole test tube of hydrochloric acid

And what we saw and I hope you can,

is that as the pink solution goes in it goes bright blue

and the bright blue is color is due to

Cobalt ions with four chloride ions so it goes to (CoCl4)2-

going from cobalt 2+ to 2- ions.

And the striking thing is of course that it's a much darker color, even though we're diluting it

If you drop the cobalt chloride into water, you see almost no color, because it's so dilute.

So the reason why you get this very intense color is because of

the change of the shape of the atoms immediately around the cobalt,

going from six round the cobalt to only four.

And this change of shape changes the quantum mechanical rules,

in which the electrons are interacting with light

So in the second experiment i want you to see what happens if you drop

cobalt chloride solution into sodium hydroxide, quite concentrated

and you would expect to see a precipitate of cobalt hydroxide, which is pink.

Now watch carefully.

As it goes in you get a precipitate a, solid but it's bright blue!

And then as you watch,

really quite slowly and satisfyingly,

it gradually goes pink to make the product that you expect.

So this is an example of a reaction,

where the starting material goes through some sort of intermediate compound and then makes the product.

And it makes the intermediate very quickly and then slowly it goes to the product

And what's happening is that

first of all, you get a mixed salt where you have both hydroxide and chloride

which is still insoluble so it precipitates.

And then, slowly, and it's slow

because it's in the solid state and has to redissolve,

the chloride is replaced by hydroxide to give you the pink color.

and it's really quite mesmerizing, how these pink crystals rain down

Cobalt is also very important as a catalyst

It is used in a variety of industrial processes,

particularly a process for converting natural gas,

or rather a mixture of carbon monoxide and hydrogen,

which can be made from natural gas,

and has the rather amusing name of syngas for synthesis gas,

and using a cobalt catalyst you can then convert it to liquid fuels for cars or lorries

And the advantage is that you can take isolated gas fields,

where there's natural gas (methane) and convert it into liquid fuel that can then be transported

Cobalt is also very toxic

We had some powdered cobalt, so-called cobalt sponge

And Neil, our technician, was really quite nervous of this poisonous powder,

but cobalt is also vital for life.

It occurs in a molecule called vitamin B12

which is present in living organisms in rather a low concentration,

but catalyzes a whole series of important biological reactions

And the structure vitamin B12, was determined, by the british chemist Dorothy Hodgkin,

who was the only woman who's won the Nobel Prize for Chemistry from the UK

So it is really a very historic structure.

So this is Neil's new device. It's a very very fancy erection.

Potentially we've used a laboratory stand, and we have an eyelet.

So this is just to act as a point, which we can raise up our cesium on a piece of string.