If you remember back to the last caesium video, Pete and Neil tried to launch a bit of caesium
metal into water with the small metallic collider and they had a few problems with surface area
and caesium still being stuck in the glass as well.
What I have been asked to do today, is take this ampoule of caesium into this piece of
machinery here which is one of our glove boxes, try and get it out of the glass so that we
can put it in as is.
Caesium has quite a surprising use, it is used to measure time. I don’t know if you
have ever thought about it but you could define one second as a fraction of a day, one sixtieth
of a minute which is which is a sixtieth of an hour which is then a twenty fourth of a
day. But the trouble with that is that you will never be able to tell if the earth was
going slower or speeding up because the length of the day would change and you would not
notice it so scientists have to have an independent way of defining the second and this is where
caesium comes in.
And so now the caesium is going in as well. Alright, so we will shut the port door
So the way in which scientists define the second is in terms of microwaves and the frequency
of the microwaves, we need a standard, something that can define a radiowave very very precisely,
and this is where caesium comes in.
So what I need to do now is open up this door here.
The point about caesium is that it is a big atom it can absorb microwaves, the absorption
of the microwave causes an electron to move from one energy level to another and the advantage
of caesium over all other materials is that this frequency is enormously precise.
It is pretty cool it is really good, it is sort of a really pale gold colour. It is still
molten at the moment.
It is rather like tuning a radio, I don’t know if you’ve ever tuned a radio but as
you turn the knob, sometimes, you don’t have to be very precise , you can put it almost
anywhere and you get your favourite station, but there are some stations where you have
to adjust it very very accurately and there is just one tiny place where you can get the
right radio station and caesium is like that, it defines the frequency very very accurately,
if you don’t hit it right it does not absorb the radiowaves and so you can use it as a
standard, so make sure so make sure that everybody has exactly the same frequency of their microwave
and then once everybody has got the same, then it is quite easy for everybody to agree
that they will count a certain number of waves as being a second.
We are going to store the caesium under oil so that it does not react with air when it
comes out. So this is ready now for Pete to chuck it in some water and we will stand very
far back when he does it.
So we have got caesium, we have taken it out of the ampoule, Neil did that the other day
with Debbie in their glove box, they have put it into a small plastic weighing boat
and immersed it in oil so it can’t react with air . Now what we need to do is a very
technical operation is to punch a hole into the plastic boat so that we can lift it out
with a piece of string so we can drop it into some water.
I’ve got my friend, Dr Red.
It is always good to be very very careful when you are doing chemistry like this, just
in case it goes wrong we have the safety procedures in place for us, in case we get surprised.
So now Neil is going to pass a piece of string through the hole so that we can put it at
the end of a pretty long fishing line so that we can drop it into water.
So this is Neil’s new device, it’s a very very fancy erection. Essentially we have used
a laboratory stand, and we have an eyelet so this is just to act as a point where we
can raise up our caesium on a piece of string. At the moment, the caesium you can see is
a lovely gold colour. Would you believe me, it’s melting.
Look at it. Oh yeah it’s very warm here today and the caesium’s melted. So we are
just going to try and freeze it again.
Well we are going to try and refreeze the caesium by cooling it with liquid nitrogen.
Ok everybody be careful.
So we have our caesium under oil. We now need to lift it up using the new device, and then
drop it in the water, and let’s see what kind of chemical reaction it does today.
Everybody ready? Neil?
Yep!
Wow, quite a spectacular reaction. As the caesium reacted with the water, gave away
its electron, off she goes, it’s caesium plus.
Awesome, it was pretty good.
Yeah, it’s pretty great you know when, when Debbie and Neil took the caesium out of the
ampoule they were really really good for us because they gave us a really large surface
area, so it could react quickly as soon as it went in the water. Generating all that
lovely hydrogen ready to explode and make a bang. Great, good chemistry.
Well, the reason that caesium reacts so violently is that it is a very large atom, so an electron
can be removed very easily, in fact if you dissolve caesium in water, on a very short
time scale, a millionth of a second or so, it dissociates into caesium-plus and an electron,
and the energy of the electron interacting with the water is enough to separate the two
and once the electron is in the water, it then reacts with the water so that H2O dissociates
into a hydrogen atom and OH-minus, so in fact what you are making is a caesium salt which
is rather like caustic soda, it’s a strong alkali and hydrogen, and it is the rapid formation
of hydrogen gas that causes part of the shock of the reaction and then the hydrogen will
usually catch fire and react with the oxygen in the air to give you a small explosion or
a big one depending how much caesium you’ve used.