In our last high-speed video you saw Caesium, and it was really good
the way it reacted quite violently,
but then we thought we should have put an indicator in the water
To see what happened water. Did it go alkali as one might expect
and how fast as the indicator change?
So now we're going to show you rubidium
and in this experiment we put Phenolphthalein and indicate into the water
which has the advantage, it is colorless in mildly acidic water and pink if the water's okay.
It's quite complicated, what happened. So I want you to watch with me on my computer and I'll try and explain to what I can see
and then you can look at the videos and see what else you can see as well.
So what we've got here, and it's almost life-size because this is the actual... Umm... trough here but with no water in it.
We've got a trough of water and then ampoule with five grams, I think it was five grams, of rubidium here
It had almost melted by the time the experiment started and the hammer is just coming down here.
The hammer you remember is our so small metallic collider for breaking glass ampoules and here it's coming.
and it hits the ampoule and breaks it
It is broken the ampoule about here above the metal
So there's a large lump of ampoule falling down with some rubidium inside it.
Here, I put some metal things in to pretend it's rubidium,
and you can see it is hitting the water just about there,
and there's some tiny pieces of Rubidium coming down here
with white smoke trails because that's reacting with the water vapor in the air.
But what I think is exciting is that this whole trough
starts flexing around, and it's really hard to bend!
And even Brady who's tougher than me Can't bend it very much.
So and it's jumping about really very strongly
and now The reaction continues. There is a small piece of rubidium metal that is jumped out.
When the rubidium lands it hits some water and itself explodes on the ground
Now I should have explained that in front of this there was a plastic shield
So you will see bits of water hitting the shield, rather like the water hitting the windshield of a car.
Now the interesting thing is if you watch carefully there's another explosion.
So not just one, but the whole thing starts all over again
and there's another eruption with the flexing of the Plastic Bowl
so what I think has happened is That when this Tube goes into the water
water rushes in and reacts with the rubidium producing explosively in amount of hydrogen
and that this great rush of gas blows all the water out of the Tube so the reaction stops
and then the water goes back in again and you get another reaction and perhaps that happens two or three times
by luck Because we didn't smash the Tube at the bottom so all the metal got wet at the same time
we've got a repeat performance without having to have an action replay or whatever.
So you get several reactions for the price of one.
So I'm just winding it back again because there's something else which you might have noticed
but I only want noticed on the second or third time
So what you'll see in various points Is that there is a strong purple color or perhaps lilac might be better.
Which is actually the emission of light.
from the vapor of the rubidium
in fact rubidium is well known to give this rather nice color
and everything is getting so hot that you can see emissions here here and so on
of this light which is perhaps slightly masked by the pink color of the indicator
indicators like this one are acids which react with an alkali
and change their structure and change their color in
this particular case with phenolphthalein the acid is colorless
and when you change structure it gets red
Brady: Neil get cleaning mate
and the reason it goes red is that as the structure changes the energy levels of the electrons
within the molecule also change and so they absorb visible light
and it looks red because in fact it's absorbing blue light so the red light can still get through
and this reaction is very fast because what happens is that
H+, and OH- ions are moving around very rapidly and they move through water at a very high speed
and so the reaction takes place very much faster than the speed of our camera
the rubidium hydroxide is reacting with the acid
the colorless indicator to make rubidium phenolphthalate plus water
so in effect H+ is leaving the acid and reacting with OH- to give water