I'm really excited. We've got two beautiful demonstrations to show you
One's a real classic - the ammonia fountain.
The other one is a completely new one we've invented ourselves called Neil's balloon
They're both based on the fact that ammonia gas is very soluble in water
and when it dissolves in water the water goes alkaline.
So if you put in an indicator that is colourless in water and red in alkaline.
When the ammonia goes in, the water goes red.
And we use the indicator Phenolphthalein.
The classic experiment is called the ammonia fountain.
It consists of a large glass bowl filled with ammonia
which has a cork or bung in the bottom with a glass tube going through it about halfway up the flask.
And the idea is, if you put the bottom of the tube into water, the ammonia starts dissolving in the water.
It creates a partial vacuum because you're absorbing gas and so the pressures going down
and the pressure of the atmosphere pushes more water into the flask.
More ammonia dissolves, so more water goes in.
Now the problem was we set it all up,
Neil set it all up. He put ammonia into the flask.
Ammonia is lighter than air. So you can just fill the flask in up by putting the tube inside it
And he then put the bung into the flask
And then before we started, we had the tube just above the surface of a large jar of water
And enough ammonia was coming out to start triggering the indicator
And the most beautiful red threads started appearing in the jar
I was so excited I nearly wanted to stop there
Then, we lowered the tube into the water,
But, there wasn't enough difference in pressure to get it started
So Neil and I decided to pour some liquid nitrogen over the top
which cooled the ammonia, reduced its pressure
and therefore began to suck in the water
And once the water started going in, it was really beautiful
[Music]
Neither Neil or I had ever seen it before
There was a slight problem that the bung hadn't been pushed in quite hard enough
So little air was leaking in as well
But that caused bubbling which probably added to the effect
And for reasons that I don't quite understand
that as it went on, the form of the liquid film that was on the glass surface changed a bit
So there was an ever-changing patterns
And also the color of the indicator changed quite a bit So it was really nice
Before we go on to the next one, just let me remind you
the reaction here is ammonia dissolving in water making it slightly alkaline
And the red colour is not part of the reaction - that's an indicator to show you that the water is alkaline
The next demonstration ...or really it's an experiment because we didn't know whether it would work,
began with my idea that we should try filling a balloon with ammonia
because ammonia is lighter than air, so I just wondered whether a balloon of ammonia would float
Not something you'd want to use at a party because if it bursts, there'd be a smell, but it does float quite nicely
Then we remembered that if you put sticky tape onto a balloon
you can then stick a pin or a needle through the tape into the balloon without bursting it
The reason for this is that when you normally prick a balloon...
when you make the first hole, the fabric runs from that hole and a slit goes up through the fabric and it breaks
But if you have the rubber held by sticky tape, it can't move
So we had the idea that we should try injecting water with Phenolphthalein into the balloon
What we hoped was that
the water would absorb the ammonia so the pressure would go down and the balloon would shrink
Of course, with the fountain, the size of the flask can't change and of course it fills up with just more and more water
So the idea here was [this'd] be a much simpler demonstration that we could do perhaps more quickly
Before we started filming, Neil practiced with a syringe needle in a nitrogen balloon
Just sticking the needle in - it worked perfectly
But then when we started filming, the first balloon, needle went in, there was an enormous bang
[bang]
And we all ran out of the room because of the smell of ammonia
The ammonia disperses very quickly so it's not dangerous
[bang]
So for the third time, I suggested we went to cello tape or scotch tape rather than plastic tape
And we used a bigger needle so we could inject the liquid faster
And it worked beautifully
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When the liquid went in, the ammonia started being absorbed and the balloon beautifully shrank
But what we didn't realize - because Neil was holding it - was that
when ammonia dissolves in water, it produces a lot of heat
There is a positive heat of dissolution - a heat of reaction
So the balloon was actually getting hotter and hotter and Neil nearly dropped it
However he managed to hang on till the balloon went from this sort of size to about the size of my clasped hands
We were all really very pleased
In a way, it's a nicer demonstration to show how the gas is disappearing into the liquid than the traditional ammonia fountain
Because in that, the size of the flask doesn't change
But really, both of them are fun and I hope you enjoyed them
[Music]