The Alchemist's Apprentices


The Alchemist's Apprentices

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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Transcript


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I'm Peter Wothers, a chemist.

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Hundreds of years ago, I would have been called an alchemist.

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I would have thought everything was made up of just four things -

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earth, air, fire and water.

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This is my lab in the University of Cambridge,

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where I'm going to explore those four ancient elements,

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using modern chemistry.

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And to help me with this task,

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I've invited 12 young students to become my apprentices.

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Coming up...

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Water. We drink it, we swim in it, but have you ever seen it explode?

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Earth. We walk on it, we build houses from it,

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but would you know how to make a metal out of it?

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Air. It's all around us and we breathe it in,

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but have you ever seen a solid lump of it?

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Fire. We know it's dangerous, we're always told to be careful,

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but how do you get the biggest bang?

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BANG!

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Three students, one lab and the awesome force of water.

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These are the Alchemist's Apprentices.

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My name's Peter Wothers

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and I'm a chemist here at the University of Cambridge.

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And I'm joined today by three apprentices,

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who are going to help me explore

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some of the very strange properties of water.

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-OK, so, what do you know about water?

-We drink it.

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That's good. OK, what's the chemical formula?

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-ALL: H2O.

-H2O. So you all know that.

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Well, this here represents a little molecule of water.

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-So, what's what in that? What do you reckon?

-Um...

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-What's the formula for water? You just told me.

-H2O.

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So therefore, two hydrogens and one O.

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-What if you cool water down, what do we get?

-ALL: Ice.

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-What temperature do we have to cool it down to?

-ALL: Zero.

-OK.

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And this is what ice looks like.

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But if we give this some energy... What happens if we heat up the ice?

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-It turns back into water.

-It turns back into water.

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So just give this one a jiggle, jiggle it around. OK.

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Yeah, OK. You've certainly melted it now.

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But what do you notice if we compare this one to this one?

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-It's not as organised and as structured.

-It's not as organised.

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-What about how much space it's taking up?

-It takes up less.

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Yeah, it's more compact now. It takes up less space.

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So in this ice structure, it's a very regular, ordered structure,

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but actually, it does take up more space.

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And this has very important consequences.

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What does this mean if we compare solid water to liquid water?

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-It expands.

-Yeah.

-Well, OK, come over here.

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'As my apprentices rightly pointed out, water expands when it freezes.

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'This means solid ice takes up more space than liquid water

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'and becomes less dense, allowing ice to float.

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'But this is actually unusual.

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'Normally, substances contract when they freeze

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'and, like this cyclohexanol, sink.

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'This unusual property explains why rivers and lakes

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'don't completely freeze in winter, and how fish survive.'

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Now, what do you think would happen

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if we filled a container completely full of water

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and then turned it into the solid form?

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This would take up more space and then expand.

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It might expand, yeah.

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-The container might crack.

-It might crack.

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But what if I used a really, really strong one?

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What about using a strong one like this? What's it made of?

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-Metal?

-Yes, it is. It's solid iron.

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-So, would this be all right?

-Yeah.

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-What do you think?

-I hope so.

-This is the lid.

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OK, so we're going to fill this completely with water

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and then cool it down. So, we'll see what happens, shall we?

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'So our cast-iron flask is filled with water

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'and suspended over a beaker of freezing solution.

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'We'll slowly lower the flask into the solution

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'and observe what happens, as the water inside freezes.

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'These experiments should never be carried out

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'unless supervised in a proper laboratory.

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'Do not try them at home.'

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So this splashing around is just as it's cooling,

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because, of course, the iron flask there is at room temperature.

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So now it should be cooling down

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and, hopefully, the water will be changing to ice.

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And it's actually broken our beaker there.

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This is what's left of our iron flask.

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It's actually split into two.

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It is the same expansive force which causes damage to homes during winter

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if water is allowed to freeze in pipes and tanks.

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But there's no risk of damage here

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because this is behind a very strong safety screen.

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So, what happens if we heat up the water,

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the liquid water to higher temperatures?

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What do we call gas water then?

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-Steam.

-Steam, exactly. That's what we're going to do.

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We're going to heat up some water

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and see how much more space it takes up when we convert it into steam.

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'Time to heat things up now

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'as we explore another incredible property of water.'

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This is forcing hot air over this inner tube.

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There's a glass tube inside here,

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all the way in here and it's coming out here. You can feel the hot air.

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-That's hot.

-OK, good.

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And in a moment, one of you is going to inject

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one cubic centimetre of water using this syringe into here,

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and we're going to see how many cubic centimetres of steam we get.

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'So as our water turns to steam,

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'it expands and pushes out the piston.

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'This drives the dial and allows us

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'to measure how much steam is generated.'

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If you had to guess, how much do you think?

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-One?

-So one cubic centimetre of water

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goes into one cubic centimetre of steam.

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-Two maybe.

-That means it will double in its volume,

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which is quite substantial. And what do you think?

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I suspect 100's there for a reason.

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You think 100's there for a reason. Well, OK.

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'Pretty confident in their guesses,

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'Jude thinks it's going to be of equal size.

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'Bish thinks it's going to double in size.

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'While Ben thinks it's going to go up 100 times as much.

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'Let's put it to the test.'

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-Who's going to inject the water?

-Me.

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OK, do you want to come around here, then, please, Ben.

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-Ready with the dial?

-Yeah.

-Off you go then, Ben, push that in.

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Are you watching it? How many cubic centimetres?

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ALL: 300.

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400.

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500.

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'In fact, none of their guesses were even close,

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'as the dial keeps going and going.'

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2,300.

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Just about stopping there, yeah.

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How many cubic centimetres have we got?

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2,300 and a bit over.

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And a bit more. Wow!

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So we've seen that one cubic centimetre of water

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turns into more than 2,000 cubic centimetres of steam

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at these temperatures.

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But what do you think would happen if we didn't try this in a piston,

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but in a closed little bottle? What do you think might happen?

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The steam would escape.

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Might escape. OK.

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'This huge expansion is very important as it helps drive turbines

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'which provide electricity for our homes and schools.

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'Time now for one more experiment to see what happens

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'if we try and contain this huge expansion.'

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What we've got here is you've seen the little...the glass tube here,

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this has again got one cubic centimetre of water in it,

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but this time, it's in a sealed glass vessel,

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which is something you should never do.

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You should never usually heat things up in a sealed vessel.

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OK, now if you just step back a bit, please.

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So we've got our one cubic centimetre of water

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and we're heating this up, OK.

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And how many cubic centimetres of steam do we get? Over, 2,000, yeah.

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-Yeah, over 2,000.

-So just keep an eye on this.

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Because the pressure's building up inside there, OK,

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and maybe the glass is just going to break.

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-BANG!

-Oh!

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-BANG!

-Oh! Oh!

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PETER CHUCKLES

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-Did you hear it?

-Yeah!

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'As the water quickly gains energy and turns to steam,

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'it has no room in which to expand, leading to the explosive result.

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'This is the reason we never heat anything up in a sealed container

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'and always need to have a release for the pressure.'

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So there we have water, one of the most familiar substances to us

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and, yet, well, as the young apprentices have just seen,

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it has some really unusual properties.

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And this makes it very useful.

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Good.

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Three students, one lab

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and the ultimate goal of getting metal from rock.

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These are the Alchemist's Apprentices.

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My name is Peter Wothers

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and this is my laboratory here in the University of Cambridge,

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where I teach chemistry.

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And now I'm joined by three apprentices.

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And we're going to be looking

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at how we can extract the modern elements from the earth.

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Can you name a few elements, do you think?

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-Hydrogen.

-Hydrogen.

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-Do you know where we can find hydrogen?

-Water.

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Hydrogen's in water. Very good. Any other elements? Amy?

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-Copper.

-Copper is an element, yes.

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-Do you know where we get that from?

-The earth.

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We do get it from the earth. Ed, any other ones?

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-Gold.

-Gold. Where do we find gold?

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Like rivers and streams and stuff.

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-OK, also, yes, it may be in rocks and so on, as well.

-Yeah.

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'They're pretty good on elements,

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'but how much do they know about metals?'

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Now, do you know the difference between metals and non-metals, then?

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Metals are magnetic sometimes.

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And they're usually shiny.

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They are usually shiny. Any other differences?

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They have a high melting point.

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'Another clue is that metals conduct electricity

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'and we can use this fact to sort out metals from non-metals.

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'I've laid out three pieces of material. Which one is the metal?'

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Which one do you think is the metal?

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-That one.

-Yes.

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OK, you think this one's definitely not metal?

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Well, it kind of could be metal.

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Because they're both kind of shiny,

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like you've both got tiny bits of shine.

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Now, I have some...

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These are just some wires here, coming to a little buzzer

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and there's a battery in here

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and when we complete the circuit...

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-BUZZ!

-..it buzzes.

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Would you like to test these, then?

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Do you think this is going to conduct?

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-I don't think it is.

-No.

-No? Well, we could try it.

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OK. And what about this one?

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-That one might.

-It might.

-Might.

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-Right, do you want to try this one?

-No.

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Definitely not.

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-Do you think this is going to conduct?

-Yeah.

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-Well, do you want to try it, then?

-BUZZ!

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It definitely conducts. So this is our copper metal.

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We want to see if we can get our copper,

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our metal out of this malachite.

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So this is the mineral, which is how we would find our copper.

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This is the same mineral, actually, this is just polished.

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But at the moment, doesn't conduct electricity,

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but it has got copper in there,

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but it's chemically combined with some other elements.

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It's got the elements oxygen and carbon in there, as well.

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'Now, then, time for some alchemy

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'as we try to extract the copper metal from our rock.

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'First, though, a little elbow grease.

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'Crushing is just a physical change, but it's still the same substance.

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'Extracting our metal will call for a chemical change.

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'These experiments should never be carried out

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'unless supervised in a proper laboratory.

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'Do not try them at home.'

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So you're going to heat this up, Nick. OK.

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And drive out some of the carbon dioxide from the ore.

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We want to test to see if there's some carbon dioxide coming out,

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so can we have some limewater?

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'The beaker contains limewater,

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'which is used to detect the presence of carbon dioxide.'

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We're getting quite a few bubbles.

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This is where we're driving out the carbon dioxide,

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so our malachite,

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it contains a carbon and oxygen, combined together with the copper.

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We're seeing a colour change.

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-OK. I think we're happy that there's carbon dioxide, yes?

-Yeah.

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Still haven't got our copper.

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So we've got copper, combined with oxygen, copper oxide here.

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And we need something else to take away this last little bit of oxygen,

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to leave the copper behind.

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'And that something is hydrogen.

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'The hydrogen will combine with the oxygen in our copper oxide

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'to make water, leaving just the copper behind.'

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We've got copper oxide in here, a big balloon of hydrogen.

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In a moment, I'm just going to open this, to let some hydrogen through

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and I'm going to light it on here.

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-That's a baby flame.

-And I'm just going to keep an eye on that.

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Oh, whoa!

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-Look at that.

-It's clearly melting away.

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'So our hydrogen has begun taking away the oxygen from the copper.

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'But let's see if my apprentices have been paying attention.'

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All the oxygen's going out.

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-The oxygen is combining...

-With the hydrogen.

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-Forming...?

-Water.

-Forming water.

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We can see some of the water collecting here, actually.

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Look at that. What you're making here is very finely-divided copper.

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'Perfect answers from the students. But have we succeeded?

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'Time for the conductivity test.'

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Let's see if we've got any metallic copper, at all.

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BUZZING

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It's definitely a metal now.

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it'll be really nice, I think, if we can make

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a little lump of solid metal, rather than the powder.

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'And to do that, we need to heat our metal

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'to over 1,000 degrees, to make it melt.

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'And a piece of charcoal is the perfect surface to do this on.

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'It won't melt, even at that high temperature.

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'As always, when working at high temperatures,

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'my apprentices stand back, to a safe distance.'

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Oh, my God, that's so cool!

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HE GASPS

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'After a few minutes heating our powder,

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'a familiar substance starts to emerge.'

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Whoa!

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That's cool!

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It's started to go harder now.

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Yes. I think we've got more of a little lump there.

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What do you think it feels like?

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It feels like metal.

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'Looks good, but will it pass the test?'

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BUZZING

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-Yeah.

-It's quite conclusively metal, isn't it?

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Nice and shiny on that side.

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BUZZING

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-Yeah.

-Very good.

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'Time to test our conductivity theory, one more time.'

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So this is our mineral, our malachite.

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Nothing at all. What about the copper oxide?

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Nothing at all.

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-And what about the metal?

-BUZZING

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Look at that. Beautiful. What do you think?

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-It's pretty cool.

-Yeah, pretty cool.

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It's quite strange, the way these two will equal this,

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but they're all the same thing.

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They've all got the same elements in there.

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So this one has the copper, combined with oxygen, combined with carbon.

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This has just the copper, combined with the oxygen,

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and this is just the copper itself.

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So they're all in this same mineral, but they do look very different.

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We haven't been able to do what the alchemists wanted to do,

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to turn one metal, say lead, into another, such as gold,

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but we've done something equally exciting.

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We've used chemistry to extract the metal copper from its ore,

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from its mineral malachite.

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And I think that's pretty exciting.

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What do you think?

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Three students, one lab and the incredible secrets of air.

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These are the Alchemist's Apprentices.

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My name is Peter Wothers and in my day job as a chemist,

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I study the elements and how they make up everything around us.

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But today I'm joined by three young apprentices

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and we're going to be looking at the properties of the air.

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How much air is in this room?

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How much do you think all the air in this room would weigh?

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How many grams?

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2,000 or 3,000?

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Well, actually, it would weigh around two million grams.

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OK, and that's two tons, which is about the same weight as two cars,

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so that's quite a lot of air here, isn't there?

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'Thankfully, air is not very dense, so we don't really feel it.

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'But what gases make up that air around us?'

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So do you know what gases are in the air?

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Nitrogen.

0:15:540:15:56

-Mainly nitrogen, what else?

-A little bit of argon.

-Oxygen.

0:15:560:15:59

Oxygen is the second most abundant. Any other gases?

0:15:590:16:01

Water vapour.

0:16:010:16:03

Carbon dioxide.

0:16:030:16:04

That's the main components in the air.

0:16:040:16:07

'They certainly know a lot about air.

0:16:070:16:09

'Let's take a closer look at one of those gases they mentioned.'

0:16:090:16:12

What do you know about carbon dioxide then, what can you tell me?

0:16:120:16:15

If you burn fossil fuels, carbon dioxide is produced.

0:16:150:16:20

That's right. Anything else you know about carbon dioxide?

0:16:200:16:23

-You breathe it out and trees breathe it in.

-Yes.

0:16:230:16:25

'All good answers.

0:16:250:16:26

'Using my specially made balance, we're going to explore

0:16:260:16:30

'one of the properties of carbon dioxide - its density.'

0:16:300:16:33

-We've got two buckets either side, and what's in the buckets?

-Air.

0:16:330:16:36

Air, oh, very good, yes.

0:16:360:16:38

There's nothing other than air, just the air around us in there.

0:16:380:16:41

'Let's see what happens

0:16:410:16:43

'when we introduce a bucket of pure carbon dioxide gas.'

0:16:430:16:46

See if you can pour that into there.

0:16:460:16:49

Look at that.

0:16:510:16:53

That's amazing.

0:16:530:16:55

So you've actually just poured invisible carbon dioxide

0:16:550:16:58

from this bucket into that bucket there.

0:16:580:17:00

'The oxygen molecules in the air we breathe

0:17:000:17:03

'consist of two oxygen atoms.

0:17:030:17:05

'Carbon dioxide is made up of two oxygen atoms

0:17:080:17:11

'and a carbon atom, so it's heavier.

0:17:110:17:14

'This heavier gas tips the balance over.'

0:17:140:17:18

So we've seen some of the properties of carbon dioxide,

0:17:180:17:21

and now we'll see if we can actually make some carbon dioxide.

0:17:210:17:24

'Carbon dioxide can be made in many ways, even just by breathing out.

0:17:240:17:29

'For this experiment we are going to make the gas from a rock

0:17:290:17:32

'called calcium carbonate.

0:17:320:17:33

'First, though, my apprentices need to earn their keep as we set about

0:17:330:17:36

'breaking up the rock.

0:17:360:17:38

'These experiments should never be carried out,

0:17:380:17:41

'unless supervised in a proper laboratory.

0:17:410:17:43

'Inside our test-tube, we've got our calcium carbonate rock.

0:17:450:17:48

'That contains calcium, carbon and oxygen, and shortly I'll be

0:17:480:17:51

'testing my apprentices, to see if they know what it's made from.'

0:17:510:17:54

We're going to try and collect some of the carbon dioxide.

0:17:540:17:58

We're going to force it out of the calcium carbonate, OK,

0:17:580:18:02

and we want to see if we can trap it.

0:18:020:18:04

-Now how do you think we can do that?

-Liquid nitrogen.

0:18:040:18:07

We could use some liquid nitrogen and that would cool it down

0:18:070:18:10

and convert it in to the solid form. That's what we'll do.

0:18:100:18:13

'Using freezing liquid nitrogen,

0:18:130:18:15

'we can cool down our carbon dioxide gas as it's produced.

0:18:150:18:19

'This will change its state, into a solid,

0:18:190:18:22

'and capture it in a test-tube, before it can escape.'

0:18:220:18:24

Now we need pretty high temperatures for this, so I'm going to use 1,000

0:18:240:18:28

degrees C, this particular flame, so the calcium carbonate contains...

0:18:280:18:33

..well, which elements do you think it's got in, calcium carbonate?

0:18:330:18:36

Calcium.

0:18:360:18:37

-Calcium, yes, clearly.

-Carbon.

0:18:370:18:39

Carbon, yes. And there's one other one.

0:18:390:18:42

-Oxygen.

-Oxygen, that's right.

0:18:420:18:44

Now, I wonder if we're getting anything forming on this side?

0:18:440:18:46

Well, we've got some white on the sides, there.

0:18:460:18:51

That could be some carbon dioxide.

0:18:510:18:54

I think we'll stop heating this, in a moment.

0:18:540:18:56

And I'm going to attach a balloon to here, in a minute,

0:18:560:18:59

and, then, maybe, when we remove this, as the CO2 turns back into

0:18:590:19:03

the gas, it might blow up the balloon. We'll see.

0:19:030:19:07

'As we take away the freezing liquid nitrogen,

0:19:090:19:12

'the carbon dioxide quickly expands back to its gaseous state.

0:19:120:19:15

'This is quite normal, as carbon dioxide is a gas

0:19:150:19:18

'at room temperature.

0:19:180:19:19

'But there is something unusual happening.'

0:19:190:19:23

This is a little block of solid carbon dioxide,

0:19:230:19:27

and all it's doing there is turning directly in to carbon dioxide gas.

0:19:270:19:33

That's quite cool. It's not melting, at all.

0:19:330:19:36

And does anyone know what this is called,

0:19:360:19:38

when a solid goes directly to a gas?

0:19:380:19:40

-Subliming.

-Very good, yes, this is subliming.

0:19:400:19:43

'Sublimation is the name of the process when a substance changes

0:19:430:19:47

'from it solid state to its gaseous state, without becoming a liquid.

0:19:470:19:51

'Because there's never any messy liquid,

0:19:510:19:54

'solid carbon dioxide is also known as dry ice.

0:19:540:19:58

'So that's the carbon dioxide produced in our experiment.

0:19:580:20:01

'But what about the calcium oxide left in the test-tube?

0:20:010:20:04

'How has THAT changed?'

0:20:040:20:06

This started off just like the rock that you chipped away.

0:20:060:20:11

That was calcium carbonate.

0:20:110:20:13

We've heated this one up, it's cooled down again now,

0:20:130:20:16

but it's changed, so it's no longer calcium carbonate, what is it?

0:20:160:20:19

-Calcium oxide.

-Calcium oxide.

0:20:190:20:21

And I'm just going to put some water on this, so put some water on here.

0:20:210:20:25

What's going to happen? What do we get?

0:20:250:20:27

-Wet rock.

-Wet rock, OK.

0:20:270:20:28

But if I give you the watering can, what I'd like you to do,

0:20:280:20:32

just sprinkle a little bit on the rocks, both on the rocks there.

0:20:320:20:35

And what have we got now?

0:20:370:20:39

Carbon dioxide?

0:20:390:20:40

No, it's not carbon dioxide. There's no carbon dioxide left in this.

0:20:400:20:43

It was only calcium oxide.

0:20:430:20:45

'As the water reacts with the calcium oxide ,it gives out heat,

0:20:450:20:49

'in what's called an exothermic process.

0:20:490:20:52

'The heat turns some of the water to steam.

0:20:520:20:55

'And what's being made?

0:20:550:20:57

'It's a substance called calcium hydroxide,

0:20:570:21:00

'which, when dissolved in water, is called limewater.

0:21:000:21:03

'Limewater is used as a test for carbon dioxide.'

0:21:030:21:07

The early alchemists thought that the air was a single substance

0:21:110:21:14

but, of course, we now know it's a mixture of different gases,

0:21:140:21:17

and if we cool these gases down, we can make first the liquids

0:21:170:21:20

and then, at even lower temperatures, the solids.

0:21:200:21:23

And these gases that make up the air have very different properties.

0:21:230:21:26

We've seen the carbon dioxide is heavier than air,

0:21:260:21:29

and we can form this by driving it out of some of the minerals

0:21:290:21:32

around us, like the calcium carbonate.

0:21:320:21:35

'Three students, one lab and lots of fire.

0:21:420:21:48

'These are the Alchemist's Apprentices.

0:21:490:21:53

My name is Peter Wothers and I'm joined

0:21:560:21:59

here in the Department of Chemistry at the University of Cambridge

0:21:590:22:02

by three new apprentices,

0:22:020:22:04

and we're going to be looking at fire.

0:22:040:22:06

So what can you tell me about fire, then?

0:22:060:22:09

Isn't it an element?

0:22:090:22:10

The Greeks used to think it was an element,

0:22:100:22:12

and it used to make up everything around us.

0:22:120:22:14

But it's not quite an element, in the modern sense, at all.

0:22:140:22:17

Yeah, I think we need to look at some fire

0:22:170:22:19

and then that might give us some more clues, all right?

0:22:190:22:22

So this is filled with gas, is it going to be very loud,

0:22:220:22:25

what do you think?

0:22:250:22:26

-Medium.

-Medium?

-Yeah.

0:22:260:22:27

Let's have a look, then, let's see what happens. Are we ready?

0:22:270:22:30

LOUD BANG ALL: Oh!

0:22:310:22:33

'Don't experiment with flammable materials at home or on your own.'

0:22:330:22:36

What did you see?

0:22:360:22:37

-Lots of heat.

-Did you see the heat?

0:22:370:22:39

Yeah. It got, like, warmer.

0:22:390:22:42

You felt some heat, did you, you felt a bit of heat?

0:22:420:22:45

'An explosive start there,

0:22:450:22:46

'but let's see what my apprentices really know about fire,

0:22:460:22:49

'with a little help from an old favourite - the Bunsen burner.'

0:22:490:22:51

How do they work?

0:22:510:22:53

There's a little valve and if you turn it, like if you turn it..

0:22:530:22:56

-Where's the little valve, do you want to show me?

-It's just there.

0:22:560:22:59

So if you turn it like that, it makes it a roaring flame,

0:22:590:23:02

which is the hottest,

0:23:020:23:03

and if you turn it like that, it makes it a safety flame.

0:23:030:23:05

-Why is this a safety flame, then?

-It's hot.

0:23:050:23:07

Because everyone can see it.

0:23:070:23:09

And if I put this in, then, you can see what's going to happen.

0:23:090:23:12

So let's just try this, shall we?

0:23:120:23:14

Just put this white tile in.

0:23:140:23:15

This black stuff, what would you call it?

0:23:150:23:17

-Soot.

-Soot, exactly. It's soot.

0:23:170:23:19

And this is - well, it's an impure form of carbon.

0:23:190:23:22

What does it tell us then? Where was the carbon initially?

0:23:220:23:26

Coming from the gas leading to the Bunsen burner.

0:23:260:23:28

Exactly. You're absolutely right.

0:23:280:23:30

It's coming from the gas that we've lit here.

0:23:300:23:32

So what we're seeing, this flame, are very hot, little particles, tiny

0:23:320:23:36

little bits of carbon, that's what gives us this nice yellow flame.

0:23:360:23:40

'Opening the valve allows more air to mix with the gas

0:23:400:23:43

'and use up black carbon.

0:23:430:23:44

'This produces a much hotter blue flame which is ideal for cooking

0:23:440:23:48

'and heating experiments.

0:23:480:23:50

'But let's see if they know exactly how hot it really is.'

0:23:500:23:53

I think the blue one's probably about 120.

0:23:530:23:56

120. What would you guess at?

0:23:560:23:59

-Probably 100.

-100.

0:23:590:24:01

'Time to put their guesses to the test, using a temperature probe.

0:24:010:24:05

'First up is the yellow safety flame.'

0:24:050:24:07

It's going up really quickly.

0:24:070:24:08

'Like all good chemists,

0:24:080:24:10

'my apprentices know they should

0:24:100:24:11

'only hold the probe at the insulated end.'

0:24:110:24:13

What's the temperature now? It is?

0:24:130:24:16

We weren't very good at guessing it.

0:24:160:24:18

We're already over 400... coming up to 500C already.

0:24:180:24:21

That's quite hot, isn't it? Now, you were guessing 100.

0:24:210:24:24

If it was 100 - well, what temperature does water boil at?

0:24:240:24:27

A hundred.

0:24:270:24:29

A hundred. So it would just be hot enough maybe to boil.

0:24:290:24:32

It's definitely much hotter than that.

0:24:320:24:34

'Next up, the roaring blue flame.

0:24:340:24:36

'Let's see how the introduction of air affects the temperature.

0:24:360:24:40

Lauren, if you want to go to the what you think is the hottest part.

0:24:400:24:43

'Lauren's right.

0:24:430:24:45

'The hottest part of the flame is just above the inner blue cone,

0:24:450:24:48

'so the temperature quickly rises.'

0:24:480:24:50

-Whoa.

-My one's gone red-hot.

0:24:500:24:52

Your one's gone red-hot.

0:24:520:24:56

And you're up to - well, this is 900C, but you're quite

0:24:560:25:00

right, Trinity, your one's actually quite cool, but it does certainly

0:25:000:25:04

show that the hottest part of the flame is right above the blue cone.

0:25:040:25:09

What if we want to get the best heat out of our fuel?

0:25:090:25:14

-We need to mix the fuel with...?

-BOTH: The air.

0:25:140:25:17

The air. To do that, we can't just burn the gas,

0:25:170:25:19

we need to mix it with...?

0:25:190:25:21

-Oxygen.

-With oxygen, right.

0:25:210:25:22

'My apprentices are right again.

0:25:220:25:25

'Oxygen is a key ingredient of fire, along with fuel and heat.

0:25:250:25:29

'Time for an experiment then, to investigate oxygen, fuel and fire.'

0:25:290:25:33

Now, these bottles that you've just brought round, actually just

0:25:330:25:37

contain oil and water and I've added some blue food colouring

0:25:370:25:40

to the water, so we're using these just to show the ratios that we're

0:25:400:25:43

going to mix our fuel and oxygen gas.

0:25:430:25:46

And we're trying to work out how to get the loudest bang.

0:25:460:25:49

'That's right.

0:25:490:25:51

'The aim of this experiment is to discover how much oxygen

0:25:510:25:54

'and fuel will make the biggest bang.

0:25:540:25:56

'We're going to use a gas called propane as our fuel,

0:25:560:25:59

'so which ratios will my apprentices choose?'

0:25:590:26:03

I think this one, because it's got more fuel.

0:26:030:26:06

So you want the 1:3, do you? OK.

0:26:060:26:08

Probably that one.

0:26:080:26:10

-So Lauren, you're going to choose the 1:1, are you?

-Yeah.

0:26:100:26:13

That sounds sensible.

0:26:130:26:14

Which means then, Trinity, I'm afraid you're left with the 1:5.

0:26:140:26:17

'And know the ratios are chosen.

0:26:170:26:19

'Lauren has chosen a ratio of 1:1, Annabel those 1:3, and Trinity 1:5.

0:26:190:26:26

'It's time to fill the balloons with our gases.

0:26:260:26:29

'We use my apparatus to first measure the volume of gas

0:26:290:26:33

'before pushing it into the balloons.

0:26:330:26:35

'First up, Lauren, who puts the same amount of oxygen

0:26:350:26:38

'and propane in to her balloon, for a 1:1 ratio.'

0:26:380:26:41

Push that in, then.

0:26:410:26:44

'Next, Annabel fills her balloon with three parts oxygen

0:26:440:26:47

'and one part fuel.'

0:26:470:26:49

There we are, perfect.

0:26:490:26:51

'And finally,

0:26:510:26:52

'Trinity adds five parts oxygen

0:26:520:26:54

'to her one part of fuel in the balloon.'

0:26:540:26:56

Good, and just hold that. Lovely.

0:26:560:26:59

'With the sound meter ready and the ear-protection

0:26:590:27:01

'securely fastened, it's time to reveal the big bang.

0:27:010:27:06

'First to pop is Lauren, with her 1:1 one ratio.'

0:27:060:27:10

BANG

0:27:100:27:11

105.4.

0:27:130:27:15

'Pretty loud.'

0:27:150:27:16

OK, ready for the next one?

0:27:160:27:18

'Can Annabel do any better, with her 3:1 ratio?'

0:27:180:27:22

BANG, BANG, BANG

0:27:220:27:24

119.

0:27:240:27:26

119? That was better, wasn't it?

0:27:260:27:28

'A shocked Annabel takes her place back at the bench.

0:27:280:27:31

'It's the turn of Trinity, with her red balloon, containing five times

0:27:310:27:34

'as much oxygen as fuel.'

0:27:340:27:36

BANG, BANG

0:27:370:27:39

116.6.

0:27:400:27:43

116.6.

0:27:430:27:45

'So Lauren's ratio of 1:1 had a reading of 105.4 decibels.

0:27:450:27:51

'Annabel's 1:3 ratio had a 119 decibels.

0:27:510:27:55

'While Trinity's 1:5 ratio had a reading of a 116.6.'

0:27:550:28:02

It's very important, then, to get the right measure of fuel

0:28:020:28:05

and oxygen to get the good combustion.

0:28:050:28:08

Did you see the difference between the flames?

0:28:080:28:11

So the first one - yes, very yellow, quite big, wasn't it?

0:28:110:28:13

it almost looked a bit sooty. But what about the other two ones?

0:28:130:28:16

Well, ours went really quickly, you could hardly see the flame.

0:28:160:28:19

There was no flame, it just went...

0:28:190:28:21

-Black.

-Exactly, it just disappeared, yes.

0:28:210:28:23

And that's because it was complete combustion there, so we

0:28:230:28:26

didn't have the little particles of carbon, of soot that were glowing.

0:28:260:28:30

That gives rise to the flame.

0:28:300:28:32

When we burn them completely, if we give them enough oxygen, then,

0:28:320:28:36

yup, we don't see the flame, we just get a very loud bang indeed.

0:28:360:28:39

So we've had some loud bangs there, some flashes,

0:28:410:28:44

but my apprentices still seem to be in one piece, which is great,

0:28:440:28:48

and I think we've learnt quite a bit about fire.

0:28:480:28:51

So thank you very much for coming along.

0:28:510:28:54

ALL: Thank you.

0:28:540:28:55

What did you like best?

0:28:550:28:56

Subtitles by Red Bee Media Ltd

0:29:020:29:05

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.


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