Name: 失去手指的化學 - 視頻元素週期表 (Losing fingers to chemistry - Periodic Table of Videos)
Uploaded: 2021-01-14T10:15:25.000Z
Duration: 4 min 30 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

After this, whenever he was lecturing the reaction,

he would hold up his hand and say, "I had a hand in that reaction."

So this time, I've got potassium dichromate,

and then finally on top of this mixture, which is in- dissolved in water, I'm going to add some diethyl ether.

Diethyl ether is an organic compound which does not mix with water.

So if I add it carefully, it should float on the surface.

there's a colorless layer here of ether, with the dichromate underneath.

So now, I put some hydrogen peroxide into this small beaker,

and we'll add a little and see what happens.

is that there's quite a violent reaction,

and the ether layer has gone bright blue.

And the reason it's gone bright blue is because

we have formed a chromium compound with the formula chromium-O₅.

Which, unusually for an inorganic compound, will dissolve in an organic solvent.

And so the hydrogen peroxide has oxidized the chromium.

It was chromium-O₄⁻², it's now chromium-O₅.

And it's important with this blue compound,

it's very intensely colored, so there isn't very much here...

but one must be very careful not to isolate this material.

a famous story of a chem- a chemistry professor in Cambridge,

whose student made a whole test tube full of this solid compound.

And the professor was shaking the test tube,

And after this, whenever he was lecturing the reaction he would hold up his hand and say,

And all the students got very frightened.

But in a long tube like this, you don't get very good mixing.

If I was to stir it with a rod or something like that,

I don't have one here, it would all react at once.

But this is quite nice to do it like this, because then you see the before and after color at the same time.

And you can see the reaction is taking place here,

which is released by the reaction, is coming up.

And you're left with some the, um, chromium in solution here,  and it's a, um, greenish color for chromium 2.

So kind of like the reaction point is like a wave that's moving down the...

But, that's nothing to do with the chemistry, that's because the mixing is so bad in this sort of vessel.

That's why chemical engineers have to design proper-shaped vessels

so that reactions go in a controlled manner.

You saw in this case it wasn't very controlled to begin with, it all splurted out of the top.

Which looks quite spectacular, but is not very good practice.

We're trying again, this time I thought to put water.

I put warm water in here so the reaction may be faster,

and I'll put in most of the acid, as well.

and now we've got enough peroxide still left.

You can see it's decolorising straight away.

字幕列表影片播放

失去手指的化學 - 視頻元素週期表 (Losing fingers to chemistry - Periodic Table of Videos)

sort

enormous

material

practice