Cambridge chemist Dr Peter Wothers offers 12 Key Stage 3 students the opportunity to join him in his laboratory to explore the four ancient elements: water, earth, air and fire.
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I'm Peter Wothers, a chemist.
Hundreds of years ago, I would have been called an alchemist.
I would have thought everything was made up of just four things -
earth, air, fire and water.
This is my lab in the University of Cambridge,
where I'm going to explore those four ancient elements,
using modern chemistry.
And to help me with this task,
I've invited 12 young students to become my apprentices.
Water. We drink it, we swim in it, but have you ever seen it explode?
Earth. We walk on it, we build houses from it,
but would you know how to make a metal out of it?
Air. It's all around us and we breathe it in,
but have you ever seen a solid lump of it?
Fire. We know it's dangerous, we're always told to be careful,
but how do you get the biggest bang?
Three students, one lab and the awesome force of water.
These are the Alchemist's Apprentices.
My name's Peter Wothers
and I'm a chemist here at the University of Cambridge.
And I'm joined today by three apprentices,
who are going to help me explore
some of the very strange properties of water.
-OK, so, what do you know about water?
-We drink it.
That's good. OK, what's the chemical formula?
-H2O. So you all know that.
Well, this here represents a little molecule of water.
-So, what's what in that? What do you reckon?
-What's the formula for water? You just told me.
So therefore, two hydrogens and one O.
-What if you cool water down, what do we get?
-What temperature do we have to cool it down to?
And this is what ice looks like.
But if we give this some energy... What happens if we heat up the ice?
-It turns back into water.
-It turns back into water.
So just give this one a jiggle, jiggle it around. OK.
Yeah, OK. You've certainly melted it now.
But what do you notice if we compare this one to this one?
-It's not as organised and as structured.
-It's not as organised.
-What about how much space it's taking up?
-It takes up less.
Yeah, it's more compact now. It takes up less space.
So in this ice structure, it's a very regular, ordered structure,
but actually, it does take up more space.
And this has very important consequences.
What does this mean if we compare solid water to liquid water?
-Well, OK, come over here.
'As my apprentices rightly pointed out, water expands when it freezes.
'This means solid ice takes up more space than liquid water
'and becomes less dense, allowing ice to float.
'But this is actually unusual.
'Normally, substances contract when they freeze
'and, like this cyclohexanol, sink.
'This unusual property explains why rivers and lakes
'don't completely freeze in winter, and how fish survive.'
Now, what do you think would happen
if we filled a container completely full of water
and then turned it into the solid form?
This would take up more space and then expand.
It might expand, yeah.
-The container might crack.
-It might crack.
But what if I used a really, really strong one?
What about using a strong one like this? What's it made of?
-Yes, it is. It's solid iron.
-So, would this be all right?
-What do you think?
-I hope so.
-This is the lid.
OK, so we're going to fill this completely with water
and then cool it down. So, we'll see what happens, shall we?
'So our cast-iron flask is filled with water
'and suspended over a beaker of freezing solution.
'We'll slowly lower the flask into the solution
'and observe what happens, as the water inside freezes.
'These experiments should never be carried out
'unless supervised in a proper laboratory.
'Do not try them at home.'
So this splashing around is just as it's cooling,
because, of course, the iron flask there is at room temperature.
So now it should be cooling down
and, hopefully, the water will be changing to ice.
And it's actually broken our beaker there.
This is what's left of our iron flask.
It's actually split into two.
It is the same expansive force which causes damage to homes during winter
if water is allowed to freeze in pipes and tanks.
But there's no risk of damage here
because this is behind a very strong safety screen.
So, what happens if we heat up the water,
the liquid water to higher temperatures?
What do we call gas water then?
-Steam, exactly. That's what we're going to do.
We're going to heat up some water
and see how much more space it takes up when we convert it into steam.
'Time to heat things up now
'as we explore another incredible property of water.'
This is forcing hot air over this inner tube.
There's a glass tube inside here,
all the way in here and it's coming out here. You can feel the hot air.
And in a moment, one of you is going to inject
one cubic centimetre of water using this syringe into here,
and we're going to see how many cubic centimetres of steam we get.
'So as our water turns to steam,
'it expands and pushes out the piston.
'This drives the dial and allows us
'to measure how much steam is generated.'
If you had to guess, how much do you think?
-So one cubic centimetre of water
goes into one cubic centimetre of steam.
-That means it will double in its volume,
which is quite substantial. And what do you think?
I suspect 100's there for a reason.
You think 100's there for a reason. Well, OK.
'Pretty confident in their guesses,
'Jude thinks it's going to be of equal size.
'Bish thinks it's going to double in size.
'While Ben thinks it's going to go up 100 times as much.
'Let's put it to the test.'
-Who's going to inject the water?
OK, do you want to come around here, then, please, Ben.
-Ready with the dial?
-Off you go then, Ben, push that in.
Are you watching it? How many cubic centimetres?
'In fact, none of their guesses were even close,
'as the dial keeps going and going.'
Just about stopping there, yeah.
How many cubic centimetres have we got?
2,300 and a bit over.
And a bit more. Wow!
So we've seen that one cubic centimetre of water
turns into more than 2,000 cubic centimetres of steam
at these temperatures.
But what do you think would happen if we didn't try this in a piston,
but in a closed little bottle? What do you think might happen?
The steam would escape.
Might escape. OK.
'This huge expansion is very important as it helps drive turbines
'which provide electricity for our homes and schools.
'Time now for one more experiment to see what happens
'if we try and contain this huge expansion.'
What we've got here is you've seen the little...the glass tube here,
this has again got one cubic centimetre of water in it,
but this time, it's in a sealed glass vessel,
which is something you should never do.
You should never usually heat things up in a sealed vessel.
OK, now if you just step back a bit, please.
So we've got our one cubic centimetre of water
and we're heating this up, OK.
And how many cubic centimetres of steam do we get? Over, 2,000, yeah.
-Yeah, over 2,000.
-So just keep an eye on this.
Because the pressure's building up inside there, OK,
and maybe the glass is just going to break.
-Did you hear it?
'As the water quickly gains energy and turns to steam,
'it has no room in which to expand, leading to the explosive result.
'This is the reason we never heat anything up in a sealed container
'and always need to have a release for the pressure.'
So there we have water, one of the most familiar substances to us
and, yet, well, as the young apprentices have just seen,
it has some really unusual properties.
And this makes it very useful.
Three students, one lab
and the ultimate goal of getting metal from rock.
These are the Alchemist's Apprentices.
My name is Peter Wothers
and this is my laboratory here in the University of Cambridge,
where I teach chemistry.
And now I'm joined by three apprentices.
And we're going to be looking
at how we can extract the modern elements from the earth.
Can you name a few elements, do you think?
-Do you know where we can find hydrogen?
Hydrogen's in water. Very good. Any other elements? Amy?
-Copper is an element, yes.
-Do you know where we get that from?
We do get it from the earth. Ed, any other ones?
-Gold. Where do we find gold?
Like rivers and streams and stuff.
-OK, also, yes, it may be in rocks and so on, as well.
'They're pretty good on elements,
'but how much do they know about metals?'
Now, do you know the difference between metals and non-metals, then?
Metals are magnetic sometimes.
And they're usually shiny.
They are usually shiny. Any other differences?
They have a high melting point.
'Another clue is that metals conduct electricity
'and we can use this fact to sort out metals from non-metals.
'I've laid out three pieces of material. Which one is the metal?'
Which one do you think is the metal?
OK, you think this one's definitely not metal?
Well, it kind of could be metal.
Because they're both kind of shiny,
like you've both got tiny bits of shine.
Now, I have some...
These are just some wires here, coming to a little buzzer
and there's a battery in here
and when we complete the circuit...
Would you like to test these, then?
Do you think this is going to conduct?
-I don't think it is.
-No? Well, we could try it.
OK. And what about this one?
-That one might.
-Right, do you want to try this one?
-Do you think this is going to conduct?
-Well, do you want to try it, then?
It definitely conducts. So this is our copper metal.
We want to see if we can get our copper,
our metal out of this malachite.
So this is the mineral, which is how we would find our copper.
This is the same mineral, actually, this is just polished.
But at the moment, doesn't conduct electricity,
but it has got copper in there,
but it's chemically combined with some other elements.
It's got the elements oxygen and carbon in there, as well.
'Now, then, time for some alchemy
'as we try to extract the copper metal from our rock.
'First, though, a little elbow grease.
'Crushing is just a physical change, but it's still the same substance.
'Extracting our metal will call for a chemical change.
'These experiments should never be carried out
'unless supervised in a proper laboratory.
'Do not try them at home.'
So you're going to heat this up, Nick. OK.
And drive out some of the carbon dioxide from the ore.
We want to test to see if there's some carbon dioxide coming out,
so can we have some limewater?
'The beaker contains limewater,
'which is used to detect the presence of carbon dioxide.'
We're getting quite a few bubbles.
This is where we're driving out the carbon dioxide,
so our malachite,
it contains a carbon and oxygen, combined together with the copper.
We're seeing a colour change.
-OK. I think we're happy that there's carbon dioxide, yes?
Still haven't got our copper.
So we've got copper, combined with oxygen, copper oxide here.
And we need something else to take away this last little bit of oxygen,
to leave the copper behind.
'And that something is hydrogen.
'The hydrogen will combine with the oxygen in our copper oxide
'to make water, leaving just the copper behind.'
We've got copper oxide in here, a big balloon of hydrogen.
In a moment, I'm just going to open this, to let some hydrogen through
and I'm going to light it on here.
-That's a baby flame.
-And I'm just going to keep an eye on that.
-Look at that.
-It's clearly melting away.
'So our hydrogen has begun taking away the oxygen from the copper.
'But let's see if my apprentices have been paying attention.'
All the oxygen's going out.
-The oxygen is combining...
-With the hydrogen.
We can see some of the water collecting here, actually.
Look at that. What you're making here is very finely-divided copper.
'Perfect answers from the students. But have we succeeded?
'Time for the conductivity test.'
Let's see if we've got any metallic copper, at all.
It's definitely a metal now.
it'll be really nice, I think, if we can make
a little lump of solid metal, rather than the powder.
'And to do that, we need to heat our metal
'to over 1,000 degrees, to make it melt.
'And a piece of charcoal is the perfect surface to do this on.
'It won't melt, even at that high temperature.
'As always, when working at high temperatures,
'my apprentices stand back, to a safe distance.'
Oh, my God, that's so cool!
'After a few minutes heating our powder,
'a familiar substance starts to emerge.'
It's started to go harder now.
Yes. I think we've got more of a little lump there.
What do you think it feels like?
It feels like metal.
'Looks good, but will it pass the test?'
-It's quite conclusively metal, isn't it?
Nice and shiny on that side.
'Time to test our conductivity theory, one more time.'
So this is our mineral, our malachite.
Nothing at all. What about the copper oxide?
Nothing at all.
-And what about the metal?
Look at that. Beautiful. What do you think?
-It's pretty cool.
-Yeah, pretty cool.
It's quite strange, the way these two will equal this,
but they're all the same thing.
They've all got the same elements in there.
So this one has the copper, combined with oxygen, combined with carbon.
This has just the copper, combined with the oxygen,
and this is just the copper itself.
So they're all in this same mineral, but they do look very different.
We haven't been able to do what the alchemists wanted to do,
to turn one metal, say lead, into another, such as gold,
but we've done something equally exciting.
We've used chemistry to extract the metal copper from its ore,
from its mineral malachite.
And I think that's pretty exciting.
What do you think?
Three students, one lab and the incredible secrets of air.
These are the Alchemist's Apprentices.
My name is Peter Wothers and in my day job as a chemist,
I study the elements and how they make up everything around us.
But today I'm joined by three young apprentices
and we're going to be looking at the properties of the air.
How much air is in this room?
How much do you think all the air in this room would weigh?
How many grams?
2,000 or 3,000?
Well, actually, it would weigh around two million grams.
OK, and that's two tons, which is about the same weight as two cars,
so that's quite a lot of air here, isn't there?
'Thankfully, air is not very dense, so we don't really feel it.
'But what gases make up that air around us?'
So do you know what gases are in the air?
-Mainly nitrogen, what else?
-A little bit of argon.
Oxygen is the second most abundant. Any other gases?
That's the main components in the air.
'They certainly know a lot about air.
'Let's take a closer look at one of those gases they mentioned.'
What do you know about carbon dioxide then, what can you tell me?
If you burn fossil fuels, carbon dioxide is produced.
That's right. Anything else you know about carbon dioxide?
-You breathe it out and trees breathe it in.
'All good answers.
'Using my specially made balance, we're going to explore
'one of the properties of carbon dioxide - its density.'
-We've got two buckets either side, and what's in the buckets?
Air, oh, very good, yes.
There's nothing other than air, just the air around us in there.
'Let's see what happens
'when we introduce a bucket of pure carbon dioxide gas.'
See if you can pour that into there.
Look at that.
So you've actually just poured invisible carbon dioxide
from this bucket into that bucket there.
'The oxygen molecules in the air we breathe
'consist of two oxygen atoms.
'Carbon dioxide is made up of two oxygen atoms
'and a carbon atom, so it's heavier.
'This heavier gas tips the balance over.'
So we've seen some of the properties of carbon dioxide,
and now we'll see if we can actually make some carbon dioxide.
'Carbon dioxide can be made in many ways, even just by breathing out.
'For this experiment we are going to make the gas from a rock
'called calcium carbonate.
'First, though, my apprentices need to earn their keep as we set about
'breaking up the rock.
'These experiments should never be carried out,
'unless supervised in a proper laboratory.
'Inside our test-tube, we've got our calcium carbonate rock.
'That contains calcium, carbon and oxygen, and shortly I'll be
'testing my apprentices, to see if they know what it's made from.'
We're going to try and collect some of the carbon dioxide.
We're going to force it out of the calcium carbonate, OK,
and we want to see if we can trap it.
-Now how do you think we can do that?
We could use some liquid nitrogen and that would cool it down
and convert it in to the solid form. That's what we'll do.
'Using freezing liquid nitrogen,
'we can cool down our carbon dioxide gas as it's produced.
'This will change its state, into a solid,
'and capture it in a test-tube, before it can escape.'
Now we need pretty high temperatures for this, so I'm going to use 1,000
degrees C, this particular flame, so the calcium carbonate contains...
..well, which elements do you think it's got in, calcium carbonate?
-Calcium, yes, clearly.
Carbon, yes. And there's one other one.
-Oxygen, that's right.
Now, I wonder if we're getting anything forming on this side?
Well, we've got some white on the sides, there.
That could be some carbon dioxide.
I think we'll stop heating this, in a moment.
And I'm going to attach a balloon to here, in a minute,
and, then, maybe, when we remove this, as the CO2 turns back into
the gas, it might blow up the balloon. We'll see.
'As we take away the freezing liquid nitrogen,
'the carbon dioxide quickly expands back to its gaseous state.
'This is quite normal, as carbon dioxide is a gas
'at room temperature.
'But there is something unusual happening.'
This is a little block of solid carbon dioxide,
and all it's doing there is turning directly in to carbon dioxide gas.
That's quite cool. It's not melting, at all.
And does anyone know what this is called,
when a solid goes directly to a gas?
-Very good, yes, this is subliming.
'Sublimation is the name of the process when a substance changes
'from it solid state to its gaseous state, without becoming a liquid.
'Because there's never any messy liquid,
'solid carbon dioxide is also known as dry ice.
'So that's the carbon dioxide produced in our experiment.
'But what about the calcium oxide left in the test-tube?
'How has THAT changed?'
This started off just like the rock that you chipped away.
That was calcium carbonate.
We've heated this one up, it's cooled down again now,
but it's changed, so it's no longer calcium carbonate, what is it?
And I'm just going to put some water on this, so put some water on here.
What's going to happen? What do we get?
-Wet rock, OK.
But if I give you the watering can, what I'd like you to do,
just sprinkle a little bit on the rocks, both on the rocks there.
And what have we got now?
No, it's not carbon dioxide. There's no carbon dioxide left in this.
It was only calcium oxide.
'As the water reacts with the calcium oxide ,it gives out heat,
'in what's called an exothermic process.
'The heat turns some of the water to steam.
'And what's being made?
'It's a substance called calcium hydroxide,
'which, when dissolved in water, is called limewater.
'Limewater is used as a test for carbon dioxide.'
The early alchemists thought that the air was a single substance
but, of course, we now know it's a mixture of different gases,
and if we cool these gases down, we can make first the liquids
and then, at even lower temperatures, the solids.
And these gases that make up the air have very different properties.
We've seen the carbon dioxide is heavier than air,
and we can form this by driving it out of some of the minerals
around us, like the calcium carbonate.
'Three students, one lab and lots of fire.
'These are the Alchemist's Apprentices.
My name is Peter Wothers and I'm joined
here in the Department of Chemistry at the University of Cambridge
by three new apprentices,
and we're going to be looking at fire.
So what can you tell me about fire, then?
Isn't it an element?
The Greeks used to think it was an element,
and it used to make up everything around us.
But it's not quite an element, in the modern sense, at all.
Yeah, I think we need to look at some fire
and then that might give us some more clues, all right?
So this is filled with gas, is it going to be very loud,
what do you think?
Let's have a look, then, let's see what happens. Are we ready?
LOUD BANG ALL: Oh!
'Don't experiment with flammable materials at home or on your own.'
What did you see?
-Lots of heat.
-Did you see the heat?
Yeah. It got, like, warmer.
You felt some heat, did you, you felt a bit of heat?
'An explosive start there,
'but let's see what my apprentices really know about fire,
'with a little help from an old favourite - the Bunsen burner.'
How do they work?
There's a little valve and if you turn it, like if you turn it..
-Where's the little valve, do you want to show me?
-It's just there.
So if you turn it like that, it makes it a roaring flame,
which is the hottest,
and if you turn it like that, it makes it a safety flame.
-Why is this a safety flame, then?
Because everyone can see it.
And if I put this in, then, you can see what's going to happen.
So let's just try this, shall we?
Just put this white tile in.
This black stuff, what would you call it?
-Soot, exactly. It's soot.
And this is - well, it's an impure form of carbon.
What does it tell us then? Where was the carbon initially?
Coming from the gas leading to the Bunsen burner.
Exactly. You're absolutely right.
It's coming from the gas that we've lit here.
So what we're seeing, this flame, are very hot, little particles, tiny
little bits of carbon, that's what gives us this nice yellow flame.
'Opening the valve allows more air to mix with the gas
'and use up black carbon.
'This produces a much hotter blue flame which is ideal for cooking
'and heating experiments.
'But let's see if they know exactly how hot it really is.'
I think the blue one's probably about 120.
120. What would you guess at?
'Time to put their guesses to the test, using a temperature probe.
'First up is the yellow safety flame.'
It's going up really quickly.
'Like all good chemists,
'my apprentices know they should
'only hold the probe at the insulated end.'
What's the temperature now? It is?
We weren't very good at guessing it.
We're already over 400... coming up to 500C already.
That's quite hot, isn't it? Now, you were guessing 100.
If it was 100 - well, what temperature does water boil at?
A hundred. So it would just be hot enough maybe to boil.
It's definitely much hotter than that.
'Next up, the roaring blue flame.
'Let's see how the introduction of air affects the temperature.
Lauren, if you want to go to the what you think is the hottest part.
'The hottest part of the flame is just above the inner blue cone,
'so the temperature quickly rises.'
-My one's gone red-hot.
Your one's gone red-hot.
And you're up to - well, this is 900C, but you're quite
right, Trinity, your one's actually quite cool, but it does certainly
show that the hottest part of the flame is right above the blue cone.
What if we want to get the best heat out of our fuel?
-We need to mix the fuel with...?
-BOTH: The air.
The air. To do that, we can't just burn the gas,
we need to mix it with...?
-With oxygen, right.
'My apprentices are right again.
'Oxygen is a key ingredient of fire, along with fuel and heat.
'Time for an experiment then, to investigate oxygen, fuel and fire.'
Now, these bottles that you've just brought round, actually just
contain oil and water and I've added some blue food colouring
to the water, so we're using these just to show the ratios that we're
going to mix our fuel and oxygen gas.
And we're trying to work out how to get the loudest bang.
'The aim of this experiment is to discover how much oxygen
'and fuel will make the biggest bang.
'We're going to use a gas called propane as our fuel,
'so which ratios will my apprentices choose?'
I think this one, because it's got more fuel.
So you want the 1:3, do you? OK.
Probably that one.
-So Lauren, you're going to choose the 1:1, are you?
That sounds sensible.
Which means then, Trinity, I'm afraid you're left with the 1:5.
'And know the ratios are chosen.
'Lauren has chosen a ratio of 1:1, Annabel those 1:3, and Trinity 1:5.
'It's time to fill the balloons with our gases.
'We use my apparatus to first measure the volume of gas
'before pushing it into the balloons.
'First up, Lauren, who puts the same amount of oxygen
'and propane in to her balloon, for a 1:1 ratio.'
Push that in, then.
'Next, Annabel fills her balloon with three parts oxygen
'and one part fuel.'
There we are, perfect.
'Trinity adds five parts oxygen
'to her one part of fuel in the balloon.'
Good, and just hold that. Lovely.
'With the sound meter ready and the ear-protection
'securely fastened, it's time to reveal the big bang.
'First to pop is Lauren, with her 1:1 one ratio.'
OK, ready for the next one?
'Can Annabel do any better, with her 3:1 ratio?'
BANG, BANG, BANG
119? That was better, wasn't it?
'A shocked Annabel takes her place back at the bench.
'It's the turn of Trinity, with her red balloon, containing five times
'as much oxygen as fuel.'
'So Lauren's ratio of 1:1 had a reading of 105.4 decibels.
'Annabel's 1:3 ratio had a 119 decibels.
'While Trinity's 1:5 ratio had a reading of a 116.6.'
It's very important, then, to get the right measure of fuel
and oxygen to get the good combustion.
Did you see the difference between the flames?
So the first one - yes, very yellow, quite big, wasn't it?
it almost looked a bit sooty. But what about the other two ones?
Well, ours went really quickly, you could hardly see the flame.
There was no flame, it just went...
-Exactly, it just disappeared, yes.
And that's because it was complete combustion there, so we
didn't have the little particles of carbon, of soot that were glowing.
That gives rise to the flame.
When we burn them completely, if we give them enough oxygen, then,
yup, we don't see the flame, we just get a very loud bang indeed.
So we've had some loud bangs there, some flashes,
but my apprentices still seem to be in one piece, which is great,
and I think we've learnt quite a bit about fire.
So thank you very much for coming along.
ALL: Thank you.
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Cambridge chemist Dr Peter Wothers offers 12 Key Stage 3 students the unique opportunity to join him in his laboratory for a master class exploring the four ancient elements: water, earth, air and fire - with explosive results.