0:00:02 > 0:00:03I'm Peter Wothers, a chemist.
0:00:03 > 0:00:06Hundreds of years ago, I would have been called an alchemist.
0:00:06 > 0:00:09I would have thought everything was made up of just four things -
0:00:09 > 0:00:12earth, air, fire and water.
0:00:12 > 0:00:15This is my lab in the University of Cambridge,
0:00:15 > 0:00:17where I'm going to explore those four ancient elements,
0:00:17 > 0:00:19using modern chemistry.
0:00:19 > 0:00:21And to help me with this task,
0:00:21 > 0:00:25I've invited 12 young students to become my apprentices.
0:00:28 > 0:00:29Coming up...
0:00:29 > 0:00:34Water. We drink it, we swim in it, but have you ever seen it explode?
0:00:35 > 0:00:39Earth. We walk on it, we build houses from it,
0:00:39 > 0:00:43but would you know how to make a metal out of it?
0:00:43 > 0:00:45Air. It's all around us and we breathe it in,
0:00:45 > 0:00:49but have you ever seen a solid lump of it?
0:00:49 > 0:00:53Fire. We know it's dangerous, we're always told to be careful,
0:00:53 > 0:00:55but how do you get the biggest bang?
0:00:55 > 0:00:57BANG!
0:00:58 > 0:01:04Three students, one lab and the awesome force of water.
0:01:04 > 0:01:07These are the Alchemist's Apprentices.
0:01:11 > 0:01:12My name's Peter Wothers
0:01:12 > 0:01:15and I'm a chemist here at the University of Cambridge.
0:01:15 > 0:01:17And I'm joined today by three apprentices,
0:01:17 > 0:01:19who are going to help me explore
0:01:19 > 0:01:22some of the very strange properties of water.
0:01:22 > 0:01:24- OK, so, what do you know about water?- We drink it.
0:01:24 > 0:01:27That's good. OK, what's the chemical formula?
0:01:27 > 0:01:29- ALL: H2O.- H2O. So you all know that.
0:01:29 > 0:01:32Well, this here represents a little molecule of water.
0:01:32 > 0:01:35- So, what's what in that? What do you reckon?- Um...
0:01:35 > 0:01:37- What's the formula for water? You just told me.- H2O.
0:01:37 > 0:01:40So therefore, two hydrogens and one O.
0:01:40 > 0:01:43- What if you cool water down, what do we get?- ALL: Ice.
0:01:43 > 0:01:45- What temperature do we have to cool it down to?- ALL: Zero.- OK.
0:01:45 > 0:01:47And this is what ice looks like.
0:01:47 > 0:01:51But if we give this some energy... What happens if we heat up the ice?
0:01:51 > 0:01:53- It turns back into water. - It turns back into water.
0:01:53 > 0:01:56So just give this one a jiggle, jiggle it around. OK.
0:01:56 > 0:01:59Yeah, OK. You've certainly melted it now.
0:01:59 > 0:02:02But what do you notice if we compare this one to this one?
0:02:02 > 0:02:05- It's not as organised and as structured.- It's not as organised.
0:02:05 > 0:02:09- What about how much space it's taking up?- It takes up less.
0:02:09 > 0:02:12Yeah, it's more compact now. It takes up less space.
0:02:12 > 0:02:15So in this ice structure, it's a very regular, ordered structure,
0:02:15 > 0:02:17but actually, it does take up more space.
0:02:17 > 0:02:19And this has very important consequences.
0:02:19 > 0:02:23What does this mean if we compare solid water to liquid water?
0:02:23 > 0:02:25- It expands.- Yeah. - Well, OK, come over here.
0:02:25 > 0:02:30'As my apprentices rightly pointed out, water expands when it freezes.
0:02:30 > 0:02:35'This means solid ice takes up more space than liquid water
0:02:35 > 0:02:38'and becomes less dense, allowing ice to float.
0:02:38 > 0:02:40'But this is actually unusual.
0:02:40 > 0:02:43'Normally, substances contract when they freeze
0:02:43 > 0:02:45'and, like this cyclohexanol, sink.
0:02:45 > 0:02:49'This unusual property explains why rivers and lakes
0:02:49 > 0:02:52'don't completely freeze in winter, and how fish survive.'
0:02:52 > 0:02:54Now, what do you think would happen
0:02:54 > 0:02:58if we filled a container completely full of water
0:02:58 > 0:03:00and then turned it into the solid form?
0:03:00 > 0:03:03This would take up more space and then expand.
0:03:03 > 0:03:05It might expand, yeah.
0:03:05 > 0:03:06- The container might crack. - It might crack.
0:03:06 > 0:03:09But what if I used a really, really strong one?
0:03:09 > 0:03:12What about using a strong one like this? What's it made of?
0:03:12 > 0:03:15- Metal?- Yes, it is. It's solid iron.
0:03:15 > 0:03:17- So, would this be all right?- Yeah.
0:03:17 > 0:03:20- What do you think? - I hope so.- This is the lid.
0:03:21 > 0:03:24OK, so we're going to fill this completely with water
0:03:24 > 0:03:27and then cool it down. So, we'll see what happens, shall we?
0:03:28 > 0:03:31'So our cast-iron flask is filled with water
0:03:31 > 0:03:34'and suspended over a beaker of freezing solution.
0:03:34 > 0:03:37'We'll slowly lower the flask into the solution
0:03:37 > 0:03:40'and observe what happens, as the water inside freezes.
0:03:40 > 0:03:43'These experiments should never be carried out
0:03:43 > 0:03:45'unless supervised in a proper laboratory.
0:03:45 > 0:03:47'Do not try them at home.'
0:03:51 > 0:03:53So this splashing around is just as it's cooling,
0:03:53 > 0:03:57because, of course, the iron flask there is at room temperature.
0:03:57 > 0:04:00So now it should be cooling down
0:04:00 > 0:04:03and, hopefully, the water will be changing to ice.
0:04:08 > 0:04:11And it's actually broken our beaker there.
0:04:11 > 0:04:14This is what's left of our iron flask.
0:04:14 > 0:04:16It's actually split into two.
0:04:17 > 0:04:21It is the same expansive force which causes damage to homes during winter
0:04:21 > 0:04:25if water is allowed to freeze in pipes and tanks.
0:04:25 > 0:04:27But there's no risk of damage here
0:04:27 > 0:04:30because this is behind a very strong safety screen.
0:04:30 > 0:04:33So, what happens if we heat up the water,
0:04:33 > 0:04:35the liquid water to higher temperatures?
0:04:35 > 0:04:37What do we call gas water then?
0:04:37 > 0:04:39- Steam.- Steam, exactly. That's what we're going to do.
0:04:39 > 0:04:41We're going to heat up some water
0:04:41 > 0:04:45and see how much more space it takes up when we convert it into steam.
0:04:45 > 0:04:46'Time to heat things up now
0:04:46 > 0:04:49'as we explore another incredible property of water.'
0:04:49 > 0:04:53This is forcing hot air over this inner tube.
0:04:53 > 0:04:55There's a glass tube inside here,
0:04:55 > 0:04:58all the way in here and it's coming out here. You can feel the hot air.
0:04:58 > 0:05:00- That's hot.- OK, good.
0:05:00 > 0:05:03And in a moment, one of you is going to inject
0:05:03 > 0:05:07one cubic centimetre of water using this syringe into here,
0:05:07 > 0:05:10and we're going to see how many cubic centimetres of steam we get.
0:05:10 > 0:05:11'So as our water turns to steam,
0:05:11 > 0:05:14'it expands and pushes out the piston.
0:05:14 > 0:05:16'This drives the dial and allows us
0:05:16 > 0:05:18'to measure how much steam is generated.'
0:05:18 > 0:05:20If you had to guess, how much do you think?
0:05:20 > 0:05:22- One?- So one cubic centimetre of water
0:05:22 > 0:05:25goes into one cubic centimetre of steam.
0:05:25 > 0:05:28- Two maybe.- That means it will double in its volume,
0:05:28 > 0:05:31which is quite substantial. And what do you think?
0:05:31 > 0:05:32I suspect 100's there for a reason.
0:05:32 > 0:05:35You think 100's there for a reason. Well, OK.
0:05:35 > 0:05:37'Pretty confident in their guesses,
0:05:37 > 0:05:40'Jude thinks it's going to be of equal size.
0:05:40 > 0:05:42'Bish thinks it's going to double in size.
0:05:42 > 0:05:46'While Ben thinks it's going to go up 100 times as much.
0:05:46 > 0:05:48'Let's put it to the test.'
0:05:48 > 0:05:50- Who's going to inject the water?- Me.
0:05:50 > 0:05:52OK, do you want to come around here, then, please, Ben.
0:05:54 > 0:05:57- Ready with the dial?- Yeah. - Off you go then, Ben, push that in.
0:05:57 > 0:05:59Are you watching it? How many cubic centimetres?
0:05:59 > 0:06:01ALL: 300.
0:06:01 > 0:06:02400.
0:06:02 > 0:06:03500.
0:06:03 > 0:06:06'In fact, none of their guesses were even close,
0:06:06 > 0:06:08'as the dial keeps going and going.'
0:06:09 > 0:06:122,300.
0:06:12 > 0:06:14Just about stopping there, yeah.
0:06:14 > 0:06:16How many cubic centimetres have we got?
0:06:16 > 0:06:192,300 and a bit over.
0:06:19 > 0:06:21And a bit more. Wow!
0:06:21 > 0:06:24So we've seen that one cubic centimetre of water
0:06:24 > 0:06:27turns into more than 2,000 cubic centimetres of steam
0:06:27 > 0:06:29at these temperatures.
0:06:29 > 0:06:32But what do you think would happen if we didn't try this in a piston,
0:06:32 > 0:06:35but in a closed little bottle? What do you think might happen?
0:06:35 > 0:06:38The steam would escape.
0:06:38 > 0:06:39Might escape. OK.
0:06:39 > 0:06:43'This huge expansion is very important as it helps drive turbines
0:06:43 > 0:06:46'which provide electricity for our homes and schools.
0:06:46 > 0:06:49'Time now for one more experiment to see what happens
0:06:49 > 0:06:52'if we try and contain this huge expansion.'
0:06:53 > 0:06:58What we've got here is you've seen the little...the glass tube here,
0:06:58 > 0:07:01this has again got one cubic centimetre of water in it,
0:07:01 > 0:07:04but this time, it's in a sealed glass vessel,
0:07:04 > 0:07:07which is something you should never do.
0:07:07 > 0:07:09You should never usually heat things up in a sealed vessel.
0:07:09 > 0:07:12OK, now if you just step back a bit, please.
0:07:14 > 0:07:17So we've got our one cubic centimetre of water
0:07:17 > 0:07:19and we're heating this up, OK.
0:07:19 > 0:07:22And how many cubic centimetres of steam do we get? Over, 2,000, yeah.
0:07:22 > 0:07:24- Yeah, over 2,000. - So just keep an eye on this.
0:07:24 > 0:07:27Because the pressure's building up inside there, OK,
0:07:27 > 0:07:30and maybe the glass is just going to break.
0:07:32 > 0:07:34- BANG! - Oh!
0:07:34 > 0:07:37- BANG! - Oh! Oh!
0:07:37 > 0:07:38PETER CHUCKLES
0:07:38 > 0:07:42- Did you hear it?- Yeah!
0:07:42 > 0:07:44'As the water quickly gains energy and turns to steam,
0:07:44 > 0:07:48'it has no room in which to expand, leading to the explosive result.
0:07:48 > 0:07:52'This is the reason we never heat anything up in a sealed container
0:07:52 > 0:07:54'and always need to have a release for the pressure.'
0:07:54 > 0:07:58So there we have water, one of the most familiar substances to us
0:07:58 > 0:08:01and, yet, well, as the young apprentices have just seen,
0:08:01 > 0:08:03it has some really unusual properties.
0:08:03 > 0:08:05And this makes it very useful.
0:08:05 > 0:08:07Good.
0:08:13 > 0:08:15Three students, one lab
0:08:15 > 0:08:19and the ultimate goal of getting metal from rock.
0:08:19 > 0:08:22These are the Alchemist's Apprentices.
0:08:25 > 0:08:26My name is Peter Wothers
0:08:26 > 0:08:29and this is my laboratory here in the University of Cambridge,
0:08:29 > 0:08:31where I teach chemistry.
0:08:31 > 0:08:34And now I'm joined by three apprentices.
0:08:34 > 0:08:35And we're going to be looking
0:08:35 > 0:08:39at how we can extract the modern elements from the earth.
0:08:39 > 0:08:40Can you name a few elements, do you think?
0:08:40 > 0:08:42- Hydrogen.- Hydrogen.
0:08:42 > 0:08:44- Do you know where we can find hydrogen?- Water.
0:08:44 > 0:08:47Hydrogen's in water. Very good. Any other elements? Amy?
0:08:47 > 0:08:49- Copper.- Copper is an element, yes.
0:08:49 > 0:08:51- Do you know where we get that from?- The earth.
0:08:51 > 0:08:53We do get it from the earth. Ed, any other ones?
0:08:53 > 0:08:56- Gold.- Gold. Where do we find gold?
0:08:56 > 0:08:57Like rivers and streams and stuff.
0:08:57 > 0:09:01- OK, also, yes, it may be in rocks and so on, as well.- Yeah.
0:09:01 > 0:09:02'They're pretty good on elements,
0:09:02 > 0:09:04'but how much do they know about metals?'
0:09:04 > 0:09:08Now, do you know the difference between metals and non-metals, then?
0:09:08 > 0:09:10Metals are magnetic sometimes.
0:09:10 > 0:09:11And they're usually shiny.
0:09:11 > 0:09:13They are usually shiny. Any other differences?
0:09:13 > 0:09:15They have a high melting point.
0:09:15 > 0:09:18'Another clue is that metals conduct electricity
0:09:18 > 0:09:21'and we can use this fact to sort out metals from non-metals.
0:09:21 > 0:09:26'I've laid out three pieces of material. Which one is the metal?'
0:09:26 > 0:09:29Which one do you think is the metal?
0:09:29 > 0:09:31- That one.- Yes.
0:09:31 > 0:09:33OK, you think this one's definitely not metal?
0:09:33 > 0:09:35Well, it kind of could be metal.
0:09:35 > 0:09:37Because they're both kind of shiny,
0:09:37 > 0:09:39like you've both got tiny bits of shine.
0:09:39 > 0:09:42Now, I have some...
0:09:42 > 0:09:45These are just some wires here, coming to a little buzzer
0:09:45 > 0:09:46and there's a battery in here
0:09:46 > 0:09:48and when we complete the circuit...
0:09:48 > 0:09:51- BUZZ! - ..it buzzes.
0:09:51 > 0:09:53Would you like to test these, then?
0:09:53 > 0:09:54Do you think this is going to conduct?
0:09:54 > 0:09:57- I don't think it is.- No. - No? Well, we could try it.
0:09:58 > 0:10:00OK. And what about this one?
0:10:00 > 0:10:02- That one might.- It might.- Might.
0:10:02 > 0:10:05- Right, do you want to try this one?- No.
0:10:05 > 0:10:08Definitely not.
0:10:08 > 0:10:10- Do you think this is going to conduct?- Yeah.
0:10:10 > 0:10:12- Well, do you want to try it, then? - BUZZ!
0:10:12 > 0:10:15It definitely conducts. So this is our copper metal.
0:10:15 > 0:10:17We want to see if we can get our copper,
0:10:17 > 0:10:20our metal out of this malachite.
0:10:20 > 0:10:24So this is the mineral, which is how we would find our copper.
0:10:24 > 0:10:28This is the same mineral, actually, this is just polished.
0:10:28 > 0:10:30But at the moment, doesn't conduct electricity,
0:10:30 > 0:10:31but it has got copper in there,
0:10:31 > 0:10:35but it's chemically combined with some other elements.
0:10:35 > 0:10:38It's got the elements oxygen and carbon in there, as well.
0:10:45 > 0:10:47'Now, then, time for some alchemy
0:10:47 > 0:10:50'as we try to extract the copper metal from our rock.
0:10:50 > 0:10:52'First, though, a little elbow grease.
0:10:53 > 0:10:58'Crushing is just a physical change, but it's still the same substance.
0:10:58 > 0:11:02'Extracting our metal will call for a chemical change.
0:11:02 > 0:11:04'These experiments should never be carried out
0:11:04 > 0:11:06'unless supervised in a proper laboratory.
0:11:06 > 0:11:08'Do not try them at home.'
0:11:08 > 0:11:10So you're going to heat this up, Nick. OK.
0:11:10 > 0:11:13And drive out some of the carbon dioxide from the ore.
0:11:13 > 0:11:16We want to test to see if there's some carbon dioxide coming out,
0:11:16 > 0:11:18so can we have some limewater?
0:11:18 > 0:11:20'The beaker contains limewater,
0:11:20 > 0:11:23'which is used to detect the presence of carbon dioxide.'
0:11:23 > 0:11:24We're getting quite a few bubbles.
0:11:24 > 0:11:26This is where we're driving out the carbon dioxide,
0:11:26 > 0:11:28so our malachite,
0:11:28 > 0:11:32it contains a carbon and oxygen, combined together with the copper.
0:11:32 > 0:11:34We're seeing a colour change.
0:11:34 > 0:11:37- OK. I think we're happy that there's carbon dioxide, yes?- Yeah.
0:11:37 > 0:11:39Still haven't got our copper.
0:11:39 > 0:11:44So we've got copper, combined with oxygen, copper oxide here.
0:11:44 > 0:11:47And we need something else to take away this last little bit of oxygen,
0:11:47 > 0:11:49to leave the copper behind.
0:11:49 > 0:11:52'And that something is hydrogen.
0:11:52 > 0:11:55'The hydrogen will combine with the oxygen in our copper oxide
0:11:55 > 0:11:59'to make water, leaving just the copper behind.'
0:11:59 > 0:12:01We've got copper oxide in here, a big balloon of hydrogen.
0:12:01 > 0:12:05In a moment, I'm just going to open this, to let some hydrogen through
0:12:05 > 0:12:07and I'm going to light it on here.
0:12:07 > 0:12:10- That's a baby flame.- And I'm just going to keep an eye on that.
0:12:10 > 0:12:12Oh, whoa!
0:12:12 > 0:12:14- Look at that. - It's clearly melting away.
0:12:14 > 0:12:18'So our hydrogen has begun taking away the oxygen from the copper.
0:12:18 > 0:12:21'But let's see if my apprentices have been paying attention.'
0:12:21 > 0:12:23All the oxygen's going out.
0:12:23 > 0:12:26- The oxygen is combining... - With the hydrogen.
0:12:26 > 0:12:29- Forming...?- Water.- Forming water.
0:12:29 > 0:12:32We can see some of the water collecting here, actually.
0:12:32 > 0:12:36Look at that. What you're making here is very finely-divided copper.
0:12:36 > 0:12:39'Perfect answers from the students. But have we succeeded?
0:12:39 > 0:12:42'Time for the conductivity test.'
0:12:42 > 0:12:44Let's see if we've got any metallic copper, at all.
0:12:44 > 0:12:47BUZZING
0:12:47 > 0:12:48It's definitely a metal now.
0:12:48 > 0:12:50it'll be really nice, I think, if we can make
0:12:50 > 0:12:55a little lump of solid metal, rather than the powder.
0:12:55 > 0:12:57'And to do that, we need to heat our metal
0:12:57 > 0:13:00'to over 1,000 degrees, to make it melt.
0:13:00 > 0:13:03'And a piece of charcoal is the perfect surface to do this on.
0:13:03 > 0:13:06'It won't melt, even at that high temperature.
0:13:06 > 0:13:08'As always, when working at high temperatures,
0:13:08 > 0:13:11'my apprentices stand back, to a safe distance.'
0:13:11 > 0:13:13Oh, my God, that's so cool!
0:13:13 > 0:13:15HE GASPS
0:13:16 > 0:13:18'After a few minutes heating our powder,
0:13:18 > 0:13:21'a familiar substance starts to emerge.'
0:13:27 > 0:13:30Whoa!
0:13:30 > 0:13:31That's cool!
0:13:31 > 0:13:33It's started to go harder now.
0:13:33 > 0:13:35Yes. I think we've got more of a little lump there.
0:13:36 > 0:13:39What do you think it feels like?
0:13:39 > 0:13:40It feels like metal.
0:13:40 > 0:13:43'Looks good, but will it pass the test?'
0:13:44 > 0:13:46BUZZING
0:13:47 > 0:13:49- Yeah.- It's quite conclusively metal, isn't it?
0:13:49 > 0:13:51Nice and shiny on that side.
0:13:51 > 0:13:53BUZZING
0:13:53 > 0:13:54- Yeah.- Very good.
0:13:54 > 0:13:59'Time to test our conductivity theory, one more time.'
0:13:59 > 0:14:01So this is our mineral, our malachite.
0:14:01 > 0:14:03Nothing at all. What about the copper oxide?
0:14:03 > 0:14:05Nothing at all.
0:14:05 > 0:14:08- And what about the metal? - BUZZING
0:14:08 > 0:14:10Look at that. Beautiful. What do you think?
0:14:10 > 0:14:12- It's pretty cool. - Yeah, pretty cool.
0:14:12 > 0:14:15It's quite strange, the way these two will equal this,
0:14:15 > 0:14:17but they're all the same thing.
0:14:17 > 0:14:19They've all got the same elements in there.
0:14:19 > 0:14:22So this one has the copper, combined with oxygen, combined with carbon.
0:14:22 > 0:14:24This has just the copper, combined with the oxygen,
0:14:24 > 0:14:26and this is just the copper itself.
0:14:26 > 0:14:29So they're all in this same mineral, but they do look very different.
0:14:32 > 0:14:35We haven't been able to do what the alchemists wanted to do,
0:14:35 > 0:14:39to turn one metal, say lead, into another, such as gold,
0:14:39 > 0:14:41but we've done something equally exciting.
0:14:41 > 0:14:47We've used chemistry to extract the metal copper from its ore,
0:14:47 > 0:14:48from its mineral malachite.
0:14:48 > 0:14:50And I think that's pretty exciting.
0:14:50 > 0:14:52What do you think?
0:14:58 > 0:15:03Three students, one lab and the incredible secrets of air.
0:15:03 > 0:15:06These are the Alchemist's Apprentices.
0:15:10 > 0:15:14My name is Peter Wothers and in my day job as a chemist,
0:15:14 > 0:15:17I study the elements and how they make up everything around us.
0:15:17 > 0:15:21But today I'm joined by three young apprentices
0:15:21 > 0:15:24and we're going to be looking at the properties of the air.
0:15:24 > 0:15:27How much air is in this room?
0:15:27 > 0:15:29How much do you think all the air in this room would weigh?
0:15:29 > 0:15:31How many grams?
0:15:31 > 0:15:322,000 or 3,000?
0:15:32 > 0:15:36Well, actually, it would weigh around two million grams.
0:15:36 > 0:15:41OK, and that's two tons, which is about the same weight as two cars,
0:15:41 > 0:15:44so that's quite a lot of air here, isn't there?
0:15:44 > 0:15:49'Thankfully, air is not very dense, so we don't really feel it.
0:15:49 > 0:15:53'But what gases make up that air around us?'
0:15:53 > 0:15:54So do you know what gases are in the air?
0:15:54 > 0:15:56Nitrogen.
0:15:56 > 0:15:59- Mainly nitrogen, what else? - A little bit of argon.- Oxygen.
0:15:59 > 0:16:01Oxygen is the second most abundant. Any other gases?
0:16:01 > 0:16:03Water vapour.
0:16:03 > 0:16:04Carbon dioxide.
0:16:04 > 0:16:07That's the main components in the air.
0:16:07 > 0:16:09'They certainly know a lot about air.
0:16:09 > 0:16:12'Let's take a closer look at one of those gases they mentioned.'
0:16:12 > 0:16:15What do you know about carbon dioxide then, what can you tell me?
0:16:15 > 0:16:20If you burn fossil fuels, carbon dioxide is produced.
0:16:20 > 0:16:23That's right. Anything else you know about carbon dioxide?
0:16:23 > 0:16:25- You breathe it out and trees breathe it in.- Yes.
0:16:25 > 0:16:26'All good answers.
0:16:26 > 0:16:30'Using my specially made balance, we're going to explore
0:16:30 > 0:16:33'one of the properties of carbon dioxide - its density.'
0:16:33 > 0:16:36- We've got two buckets either side, and what's in the buckets?- Air.
0:16:36 > 0:16:38Air, oh, very good, yes.
0:16:38 > 0:16:41There's nothing other than air, just the air around us in there.
0:16:41 > 0:16:43'Let's see what happens
0:16:43 > 0:16:46'when we introduce a bucket of pure carbon dioxide gas.'
0:16:46 > 0:16:49See if you can pour that into there.
0:16:51 > 0:16:53Look at that.
0:16:53 > 0:16:55That's amazing.
0:16:55 > 0:16:58So you've actually just poured invisible carbon dioxide
0:16:58 > 0:17:00from this bucket into that bucket there.
0:17:00 > 0:17:03'The oxygen molecules in the air we breathe
0:17:03 > 0:17:05'consist of two oxygen atoms.
0:17:08 > 0:17:11'Carbon dioxide is made up of two oxygen atoms
0:17:11 > 0:17:14'and a carbon atom, so it's heavier.
0:17:14 > 0:17:18'This heavier gas tips the balance over.'
0:17:18 > 0:17:21So we've seen some of the properties of carbon dioxide,
0:17:21 > 0:17:24and now we'll see if we can actually make some carbon dioxide.
0:17:24 > 0:17:29'Carbon dioxide can be made in many ways, even just by breathing out.
0:17:29 > 0:17:32'For this experiment we are going to make the gas from a rock
0:17:32 > 0:17:33'called calcium carbonate.
0:17:33 > 0:17:36'First, though, my apprentices need to earn their keep as we set about
0:17:36 > 0:17:38'breaking up the rock.
0:17:38 > 0:17:41'These experiments should never be carried out,
0:17:41 > 0:17:43'unless supervised in a proper laboratory.
0:17:45 > 0:17:48'Inside our test-tube, we've got our calcium carbonate rock.
0:17:48 > 0:17:51'That contains calcium, carbon and oxygen, and shortly I'll be
0:17:51 > 0:17:54'testing my apprentices, to see if they know what it's made from.'
0:17:54 > 0:17:58We're going to try and collect some of the carbon dioxide.
0:17:58 > 0:18:02We're going to force it out of the calcium carbonate, OK,
0:18:02 > 0:18:04and we want to see if we can trap it.
0:18:04 > 0:18:07- Now how do you think we can do that?- Liquid nitrogen.
0:18:07 > 0:18:10We could use some liquid nitrogen and that would cool it down
0:18:10 > 0:18:13and convert it in to the solid form. That's what we'll do.
0:18:13 > 0:18:15'Using freezing liquid nitrogen,
0:18:15 > 0:18:19'we can cool down our carbon dioxide gas as it's produced.
0:18:19 > 0:18:22'This will change its state, into a solid,
0:18:22 > 0:18:24'and capture it in a test-tube, before it can escape.'
0:18:24 > 0:18:28Now we need pretty high temperatures for this, so I'm going to use 1,000
0:18:28 > 0:18:33degrees C, this particular flame, so the calcium carbonate contains...
0:18:33 > 0:18:36..well, which elements do you think it's got in, calcium carbonate?
0:18:36 > 0:18:37Calcium.
0:18:37 > 0:18:39- Calcium, yes, clearly.- Carbon.
0:18:39 > 0:18:42Carbon, yes. And there's one other one.
0:18:42 > 0:18:44- Oxygen.- Oxygen, that's right.
0:18:44 > 0:18:46Now, I wonder if we're getting anything forming on this side?
0:18:46 > 0:18:51Well, we've got some white on the sides, there.
0:18:51 > 0:18:54That could be some carbon dioxide.
0:18:54 > 0:18:56I think we'll stop heating this, in a moment.
0:18:56 > 0:18:59And I'm going to attach a balloon to here, in a minute,
0:18:59 > 0:19:03and, then, maybe, when we remove this, as the CO2 turns back into
0:19:03 > 0:19:07the gas, it might blow up the balloon. We'll see.
0:19:09 > 0:19:12'As we take away the freezing liquid nitrogen,
0:19:12 > 0:19:15'the carbon dioxide quickly expands back to its gaseous state.
0:19:15 > 0:19:18'This is quite normal, as carbon dioxide is a gas
0:19:18 > 0:19:19'at room temperature.
0:19:19 > 0:19:23'But there is something unusual happening.'
0:19:23 > 0:19:27This is a little block of solid carbon dioxide,
0:19:27 > 0:19:33and all it's doing there is turning directly in to carbon dioxide gas.
0:19:33 > 0:19:36That's quite cool. It's not melting, at all.
0:19:36 > 0:19:38And does anyone know what this is called,
0:19:38 > 0:19:40when a solid goes directly to a gas?
0:19:40 > 0:19:43- Subliming. - Very good, yes, this is subliming.
0:19:43 > 0:19:47'Sublimation is the name of the process when a substance changes
0:19:47 > 0:19:51'from it solid state to its gaseous state, without becoming a liquid.
0:19:51 > 0:19:54'Because there's never any messy liquid,
0:19:54 > 0:19:58'solid carbon dioxide is also known as dry ice.
0:19:58 > 0:20:01'So that's the carbon dioxide produced in our experiment.
0:20:01 > 0:20:04'But what about the calcium oxide left in the test-tube?
0:20:04 > 0:20:06'How has THAT changed?'
0:20:06 > 0:20:11This started off just like the rock that you chipped away.
0:20:11 > 0:20:13That was calcium carbonate.
0:20:13 > 0:20:16We've heated this one up, it's cooled down again now,
0:20:16 > 0:20:19but it's changed, so it's no longer calcium carbonate, what is it?
0:20:19 > 0:20:21- Calcium oxide.- Calcium oxide.
0:20:21 > 0:20:25And I'm just going to put some water on this, so put some water on here.
0:20:25 > 0:20:27What's going to happen? What do we get?
0:20:27 > 0:20:28- Wet rock.- Wet rock, OK.
0:20:28 > 0:20:32But if I give you the watering can, what I'd like you to do,
0:20:32 > 0:20:35just sprinkle a little bit on the rocks, both on the rocks there.
0:20:37 > 0:20:39And what have we got now?
0:20:39 > 0:20:40Carbon dioxide?
0:20:40 > 0:20:43No, it's not carbon dioxide. There's no carbon dioxide left in this.
0:20:43 > 0:20:45It was only calcium oxide.
0:20:45 > 0:20:49'As the water reacts with the calcium oxide ,it gives out heat,
0:20:49 > 0:20:52'in what's called an exothermic process.
0:20:52 > 0:20:55'The heat turns some of the water to steam.
0:20:55 > 0:20:57'And what's being made?
0:20:57 > 0:21:00'It's a substance called calcium hydroxide,
0:21:00 > 0:21:03'which, when dissolved in water, is called limewater.
0:21:03 > 0:21:07'Limewater is used as a test for carbon dioxide.'
0:21:11 > 0:21:14The early alchemists thought that the air was a single substance
0:21:14 > 0:21:17but, of course, we now know it's a mixture of different gases,
0:21:17 > 0:21:20and if we cool these gases down, we can make first the liquids
0:21:20 > 0:21:23and then, at even lower temperatures, the solids.
0:21:23 > 0:21:26And these gases that make up the air have very different properties.
0:21:26 > 0:21:29We've seen the carbon dioxide is heavier than air,
0:21:29 > 0:21:32and we can form this by driving it out of some of the minerals
0:21:32 > 0:21:35around us, like the calcium carbonate.
0:21:42 > 0:21:48'Three students, one lab and lots of fire.
0:21:49 > 0:21:53'These are the Alchemist's Apprentices.
0:21:56 > 0:21:59My name is Peter Wothers and I'm joined
0:21:59 > 0:22:02here in the Department of Chemistry at the University of Cambridge
0:22:02 > 0:22:04by three new apprentices,
0:22:04 > 0:22:06and we're going to be looking at fire.
0:22:06 > 0:22:09So what can you tell me about fire, then?
0:22:09 > 0:22:10Isn't it an element?
0:22:10 > 0:22:12The Greeks used to think it was an element,
0:22:12 > 0:22:14and it used to make up everything around us.
0:22:14 > 0:22:17But it's not quite an element, in the modern sense, at all.
0:22:17 > 0:22:19Yeah, I think we need to look at some fire
0:22:19 > 0:22:22and then that might give us some more clues, all right?
0:22:22 > 0:22:25So this is filled with gas, is it going to be very loud,
0:22:25 > 0:22:26what do you think?
0:22:26 > 0:22:27- Medium.- Medium?- Yeah.
0:22:27 > 0:22:30Let's have a look, then, let's see what happens. Are we ready?
0:22:31 > 0:22:33LOUD BANG ALL: Oh!
0:22:33 > 0:22:36'Don't experiment with flammable materials at home or on your own.'
0:22:36 > 0:22:37What did you see?
0:22:37 > 0:22:39- Lots of heat.- Did you see the heat?
0:22:39 > 0:22:42Yeah. It got, like, warmer.
0:22:42 > 0:22:45You felt some heat, did you, you felt a bit of heat?
0:22:45 > 0:22:46'An explosive start there,
0:22:46 > 0:22:49'but let's see what my apprentices really know about fire,
0:22:49 > 0:22:51'with a little help from an old favourite - the Bunsen burner.'
0:22:51 > 0:22:53How do they work?
0:22:53 > 0:22:56There's a little valve and if you turn it, like if you turn it..
0:22:56 > 0:22:59- Where's the little valve, do you want to show me?- It's just there.
0:22:59 > 0:23:02So if you turn it like that, it makes it a roaring flame,
0:23:02 > 0:23:03which is the hottest,
0:23:03 > 0:23:05and if you turn it like that, it makes it a safety flame.
0:23:05 > 0:23:07- Why is this a safety flame, then? - It's hot.
0:23:07 > 0:23:09Because everyone can see it.
0:23:09 > 0:23:12And if I put this in, then, you can see what's going to happen.
0:23:12 > 0:23:14So let's just try this, shall we?
0:23:14 > 0:23:15Just put this white tile in.
0:23:15 > 0:23:17This black stuff, what would you call it?
0:23:17 > 0:23:19- Soot.- Soot, exactly. It's soot.
0:23:19 > 0:23:22And this is - well, it's an impure form of carbon.
0:23:22 > 0:23:26What does it tell us then? Where was the carbon initially?
0:23:26 > 0:23:28Coming from the gas leading to the Bunsen burner.
0:23:28 > 0:23:30Exactly. You're absolutely right.
0:23:30 > 0:23:32It's coming from the gas that we've lit here.
0:23:32 > 0:23:36So what we're seeing, this flame, are very hot, little particles, tiny
0:23:36 > 0:23:40little bits of carbon, that's what gives us this nice yellow flame.
0:23:40 > 0:23:43'Opening the valve allows more air to mix with the gas
0:23:43 > 0:23:44'and use up black carbon.
0:23:44 > 0:23:48'This produces a much hotter blue flame which is ideal for cooking
0:23:48 > 0:23:50'and heating experiments.
0:23:50 > 0:23:53'But let's see if they know exactly how hot it really is.'
0:23:53 > 0:23:56I think the blue one's probably about 120.
0:23:56 > 0:23:59120. What would you guess at?
0:23:59 > 0:24:01- Probably 100.- 100.
0:24:01 > 0:24:05'Time to put their guesses to the test, using a temperature probe.
0:24:05 > 0:24:07'First up is the yellow safety flame.'
0:24:07 > 0:24:08It's going up really quickly.
0:24:08 > 0:24:10'Like all good chemists,
0:24:10 > 0:24:11'my apprentices know they should
0:24:11 > 0:24:13'only hold the probe at the insulated end.'
0:24:13 > 0:24:16What's the temperature now? It is?
0:24:16 > 0:24:18We weren't very good at guessing it.
0:24:18 > 0:24:21We're already over 400... coming up to 500C already.
0:24:21 > 0:24:24That's quite hot, isn't it? Now, you were guessing 100.
0:24:24 > 0:24:27If it was 100 - well, what temperature does water boil at?
0:24:27 > 0:24:29A hundred.
0:24:29 > 0:24:32A hundred. So it would just be hot enough maybe to boil.
0:24:32 > 0:24:34It's definitely much hotter than that.
0:24:34 > 0:24:36'Next up, the roaring blue flame.
0:24:36 > 0:24:40'Let's see how the introduction of air affects the temperature.
0:24:40 > 0:24:43Lauren, if you want to go to the what you think is the hottest part.
0:24:43 > 0:24:45'Lauren's right.
0:24:45 > 0:24:48'The hottest part of the flame is just above the inner blue cone,
0:24:48 > 0:24:50'so the temperature quickly rises.'
0:24:50 > 0:24:52- Whoa.- My one's gone red-hot.
0:24:52 > 0:24:56Your one's gone red-hot.
0:24:56 > 0:25:00And you're up to - well, this is 900C, but you're quite
0:25:00 > 0:25:04right, Trinity, your one's actually quite cool, but it does certainly
0:25:04 > 0:25:09show that the hottest part of the flame is right above the blue cone.
0:25:09 > 0:25:14What if we want to get the best heat out of our fuel?
0:25:14 > 0:25:17- We need to mix the fuel with...? - BOTH: The air.
0:25:17 > 0:25:19The air. To do that, we can't just burn the gas,
0:25:19 > 0:25:21we need to mix it with...?
0:25:21 > 0:25:22- Oxygen.- With oxygen, right.
0:25:22 > 0:25:25'My apprentices are right again.
0:25:25 > 0:25:29'Oxygen is a key ingredient of fire, along with fuel and heat.
0:25:29 > 0:25:33'Time for an experiment then, to investigate oxygen, fuel and fire.'
0:25:33 > 0:25:37Now, these bottles that you've just brought round, actually just
0:25:37 > 0:25:40contain oil and water and I've added some blue food colouring
0:25:40 > 0:25:43to the water, so we're using these just to show the ratios that we're
0:25:43 > 0:25:46going to mix our fuel and oxygen gas.
0:25:46 > 0:25:49And we're trying to work out how to get the loudest bang.
0:25:49 > 0:25:51'That's right.
0:25:51 > 0:25:54'The aim of this experiment is to discover how much oxygen
0:25:54 > 0:25:56'and fuel will make the biggest bang.
0:25:56 > 0:25:59'We're going to use a gas called propane as our fuel,
0:25:59 > 0:26:03'so which ratios will my apprentices choose?'
0:26:03 > 0:26:06I think this one, because it's got more fuel.
0:26:06 > 0:26:08So you want the 1:3, do you? OK.
0:26:08 > 0:26:10Probably that one.
0:26:10 > 0:26:13- So Lauren, you're going to choose the 1:1, are you?- Yeah.
0:26:13 > 0:26:14That sounds sensible.
0:26:14 > 0:26:17Which means then, Trinity, I'm afraid you're left with the 1:5.
0:26:17 > 0:26:19'And know the ratios are chosen.
0:26:19 > 0:26:26'Lauren has chosen a ratio of 1:1, Annabel those 1:3, and Trinity 1:5.
0:26:26 > 0:26:29'It's time to fill the balloons with our gases.
0:26:29 > 0:26:33'We use my apparatus to first measure the volume of gas
0:26:33 > 0:26:35'before pushing it into the balloons.
0:26:35 > 0:26:38'First up, Lauren, who puts the same amount of oxygen
0:26:38 > 0:26:41'and propane in to her balloon, for a 1:1 ratio.'
0:26:41 > 0:26:44Push that in, then.
0:26:44 > 0:26:47'Next, Annabel fills her balloon with three parts oxygen
0:26:47 > 0:26:49'and one part fuel.'
0:26:49 > 0:26:51There we are, perfect.
0:26:51 > 0:26:52'And finally,
0:26:52 > 0:26:54'Trinity adds five parts oxygen
0:26:54 > 0:26:56'to her one part of fuel in the balloon.'
0:26:56 > 0:26:59Good, and just hold that. Lovely.
0:26:59 > 0:27:01'With the sound meter ready and the ear-protection
0:27:01 > 0:27:06'securely fastened, it's time to reveal the big bang.
0:27:06 > 0:27:10'First to pop is Lauren, with her 1:1 one ratio.'
0:27:10 > 0:27:11BANG
0:27:13 > 0:27:15105.4.
0:27:15 > 0:27:16'Pretty loud.'
0:27:16 > 0:27:18OK, ready for the next one?
0:27:18 > 0:27:22'Can Annabel do any better, with her 3:1 ratio?'
0:27:22 > 0:27:24BANG, BANG, BANG
0:27:24 > 0:27:26119.
0:27:26 > 0:27:28119? That was better, wasn't it?
0:27:28 > 0:27:31'A shocked Annabel takes her place back at the bench.
0:27:31 > 0:27:34'It's the turn of Trinity, with her red balloon, containing five times
0:27:34 > 0:27:36'as much oxygen as fuel.'
0:27:37 > 0:27:39BANG, BANG
0:27:40 > 0:27:43116.6.
0:27:43 > 0:27:45116.6.
0:27:45 > 0:27:51'So Lauren's ratio of 1:1 had a reading of 105.4 decibels.
0:27:51 > 0:27:55'Annabel's 1:3 ratio had a 119 decibels.
0:27:55 > 0:28:02'While Trinity's 1:5 ratio had a reading of a 116.6.'
0:28:02 > 0:28:05It's very important, then, to get the right measure of fuel
0:28:05 > 0:28:08and oxygen to get the good combustion.
0:28:08 > 0:28:11Did you see the difference between the flames?
0:28:11 > 0:28:13So the first one - yes, very yellow, quite big, wasn't it?
0:28:13 > 0:28:16it almost looked a bit sooty. But what about the other two ones?
0:28:16 > 0:28:19Well, ours went really quickly, you could hardly see the flame.
0:28:19 > 0:28:21There was no flame, it just went...
0:28:21 > 0:28:23- Black. - Exactly, it just disappeared, yes.
0:28:23 > 0:28:26And that's because it was complete combustion there, so we
0:28:26 > 0:28:30didn't have the little particles of carbon, of soot that were glowing.
0:28:30 > 0:28:32That gives rise to the flame.
0:28:32 > 0:28:36When we burn them completely, if we give them enough oxygen, then,
0:28:36 > 0:28:39yup, we don't see the flame, we just get a very loud bang indeed.
0:28:41 > 0:28:44So we've had some loud bangs there, some flashes,
0:28:44 > 0:28:48but my apprentices still seem to be in one piece, which is great,
0:28:48 > 0:28:51and I think we've learnt quite a bit about fire.
0:28:51 > 0:28:54So thank you very much for coming along.
0:28:54 > 0:28:55ALL: Thank you.
0:28:55 > 0:28:56What did you like best?
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