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  • (Piano music)

  • Vanadium, element number 23,

  • the third of the so-called "transition metals,"

  • so it lies between titanium and chromium

  • in the Periodic Table.

  • I don't know a huge amount about the chemistry

  • of vanadium. I've never actually seen vanadium metal,

  • so let's have a look at it.

  • It's in a really quite historic box.

  • It's wire; it's not easy to open.

  • And you can see there's a coil

  • of fairly black-ish coloured wire.

  • There are several things that interest me:

  • first of all that you can make wire as thin as that,

  • and secondly, that it doesn't look very shiny,

  • possibly it's got an oxide layer on the surface.

  • I've been given another sample: of vanadium powder,

  • but vanadium powder can catch fire quite easily,

  • and so I don't really want to take it out

  • because we might have a fire here on the table

  • in my office!

  • Vanadium metal is quite light,

  • and it is used in a variety of alloys.

  • It is also like many of the transition metals,

  • you can have different so-called "oxidation states"

  • with different numbers of electrons

  • around the vanadium atom.

  • Now, there's a really nice demonstration

  • which you should watch carefully

  • because it's what our first-year students do.

  • So if you come to this university, and several others,

  • if you know this,

  • you'll get better marks on your Practical!

  • Darren, my colleague, really enjoys doing this reaction.

  • [Dr. Darren Walsh] Vanadium five.

  • It's a yellow solution of ammonium metavanadate.

  • As you can see, it's a nice yellow colour,

  • and one of the really nice things about

  • the various oxidation states of vanadium

  • is that they're different colours.

  • So what we have here is we have a metal amalgam.

  • Now this is mercury, as you can see

  • we have mercury with some zinc in it.

  • The really nice thing about this amalgam is

  • that we can convince some electrons to jump

  • from this metal amalgam onto some other species.

  • So remember: vanadium five,

  • and I'm gonna put in here a glug of vanadium five.

  • It's not a scientific quantity, that's... that's,

  • that's uh... A glug is... It's a good glug.

  • The vanadium solution is sitting on top

  • of the mercury-zinc amalgam,

  • and hopefully, what I'm a-gonna do is by shaking it up

  • I'm gonna convince some of the electrons in the metal

  • to jump onto the vanadium species,

  • changing the oxidation state of the vanadium.

  • As I do it, hopefully we'll see a colour change.

  • Can you see the yellow?

  • [Brady Haran] Yeah I can, yeah.

  • [Dr. Walsh] Alright, so let's see...

  • So now: a nice blue colour, right?

  • And the blue colour, I happen to know, is vanadium four.

  • Alright? So each of the vanadium species

  • has gained one electron, changing its oxidation state,

  • or it has been "reduced."

  • So if I shake it a bit more, I'm gonna see

  • can we convince more of the metal to give up electrons.

  • Alright? So I think we're looking for

  • a nice green colour,

  • and you can see it's got a kind of a green colour there,

  • Can you see that as green?

  • We've gone from vanadium five, to four, to three.

  • OK, so now I need to shake it up

  • a lot to see can I convince another electron to go

  • and access vanadium two.

  • So, let's see. And this is... 'cos mercury is so heavy!

  • This is slightly hard work.

  • So there we go!

  • Purple.

  • Vanadium two, so we've gone vanadium 5, 4, 3, 2.

  • Four different oxidation states of vanadium,

  • resulting in the really nice purple

  • vanadium two species.

  • And then what would happen is,

  • if we put that on the bench

  • and left the lid off,

  • oxygen can obviously...the air can get into the container,

  • and what will happen is we will oxidize

  • this solution again. So if we waited for long enough,

  • we would see the colours go in reverse.

  • [Sir Martyn] You can find vanadium in nature.

  • There are mushrooms:

  • the sort of red ones with white spots

  • that faeries and elves sit on in faery tales

  • (I never know the difference

  • between mushrooms and toadstools...

  • the things that grow in forests),

  • and in this mushroom, or maybe toadstool,

  • nobody's quite sure

  • why there are vanadium compounds.

  • One idea is they just may be a poison

  • to discourage people from eating it --

  • or not people, but animals, slugs, worms.

  • The other theory is that the vanadium

  • may react with hydrogen peroxide,

  • which can sometimes be formed

  • in biochemical processes, and which would otherwise

  • attack more important molecules

  • to the life of the mushroom. Or toadstool.

  • But I think it's really quite interesting

  • that a mushroom, or a toadstool,

  • can do good vanadium chemistry.

  • ...match on a stick to blow up balloons with hydrogen.

  • And the thing that's always puzzled me

  • is that when they blow up,

  • the flame has a reddish colour,

  • and it's well known that hydrogen, when it burns,

  • for example in a Bunson burner or something like that,

  • gives an almost colourless flame.

(Piano music)

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釩 - 視頻週期表 (Vanadium - Periodic Table of Videos)

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    林宜悉 發佈於 2021 年 01 月 14 日
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