Name: 鉻--地球上最堅硬的金屬! (Chromium - The HARDEST METAL ON EARTH!)
Uploaded: 2021-01-14T07:14:44.000Z
Duration: 9 min 6 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。

Hello everyone today, I want to tell you about the hardest metal on earth

Chromium. As usual, let's see where Roman is in the periodic table of chemical elements.

There it is, hiding behind the Vanadium in the sixth group and yes

I did not deceive you is true that Chromium has the highest hardness of all metals

based of the Mohs scale that shows the resistance of a mineral to scratching.

externally pure Chromium is a lustreless white metal that does not tarnish in air to demonstrate the main feature of chromium

I'll scratch an ordinary silicate glass with it.

usual you cannot fool physics, Chromium easily scratch the surface of the glass leaving a clearly discernible markings.

Also, I think that the hardness of Chromium is very much dependant of its purity.

Metallic chromium is obtained from the chromium or mineral by reducing it using carbon to produce

Ferrochromium an alloy of Chromium and Iron which is used in production of stainless steel.

We will now turn to the chemical properties of Chromium, which this metal is highly enriched with even the name of the metal

This name came to pass due to the fact that Chromium compounds can have almost all the colors of a rainbow.

In laboratory the most common Chromium compound is Potassium dichromate it is used often in analytical chemistry

or to clean chemical dishes from the very stubborn dirt

compound in the production of chromium metal from ore. If you mix the potassium dichromate with any reducing

agent for example aluminium powder and then ignited

You'll see a very violent reaction that will produce particles of chromium metal

Potassium dichromate is very soluble in water

In this compound Chromium has an oxidation state of blue 6

If you add a little bit of alkali i.e sodium hydroxide to the orange solution of potassium dichromate

the dichromate will turn into chromate and

Become yellow in the oxidation state of plus 6 Chromium may have a yellow and orange color

Depending on the acidity of the environment however

That's not all if you add acid to the solution of potassium dichromate and also any reducing

agent for example potassium metabisulfite

There will be a reaction in which sulfur from metabisulfite will donate

Electrons to chromium and will be restored to its trivalent state therefore

Changing t's colour to green compounds of trivalent chromium have a green color

This is possible to prove with another reaction in order to do it

Let's take another orange chromium compound ammonium dichromate

in which chromium also has an oxidation state of plus 6

Igniting this orange powder and where do we see ammonium dichromate started decomposing by itself?

Forming a dark green substance chromium oxide due to the fact that formed chromium oxide has a porous particle

structure it begins to occupy a larger volume and

Over time it might seem that this green substance is being formed just out of nowhere

But there are no miracles chromium oxide simply forms with nitrogen and water vapor

That are also formed during this reaction as a result from a small amount of ammonium dichromate

We got a whole pile of Corona oxide is a form of a date volcano

Fun fact this reaction is actually called the volcano of ammonium dichromate

Better not to throw away as it can be easily used to make a gooey paste in

The human oxide is the main component as an inert abrasive substance the Chromium an oxide has some unusual

properties for example if you fill a flask with ammonia gas

And then add some red hot chromium oxide in such conditions ammonia gas can react with oxygen

conditions does not occur in this reaction the chromium offset was the catalyst for the oxidation of ammonia in

Oxygen also the chromium oxide can oxidize at another acidic

aldehyde if you simply light a piece of a cotton wool

Impregnated with ethanol the alcohol will just burn out however if you scatter the Chromium oxide over it

It will limit assist of the oxygen in air when using the substance it's possible to observe the residual glow

This glow is caused by the oxidation of ethanol on the surface of the chromium oxide so called

catalytic oxidation in which the ethanol is oxidized to acetic aldehyde

Similar to the smell that can be felt in the morning after a hangover as the ethanol in our body is also

In addition to the trivalent compounds Chromium can also have divalent compounds for which we will now conduct another

Let's take a test tube and for a solution of potassium dichromate in hydrochloric acid into it then we'll add a few

granules of zinc into the tube during the reaction of zinc with the hydrochloric acid

Atomic hydrogen is formed which restores chromium from hexavalent state

To trivalent and as a result the solution gradually becomes green

atomic hydrogen is an extremely strong reducing agent and

Because of that it gives away another electron to the chromium atom

resultant in it becoming bivalent and the solution acquires a bluish color

This color exactly is what the divalent Chromium compounds have

So now we have a whole set of colored Chromium compound of different oxidation states true

That's not all Chromium compounds can also be used for another colorful experiment to create a flag in a test tube

To conduct this experiment. We'll need a solution of potassium dichromate

Diethyl ether has a low density, so it will float on the surface of the solution of potassium dichromate

next add a small amount of sulfuric acid solution to our mix and to start the reaction add a

Few drops of 20 percent hydrogen peroxide into the test tube

After adding the hydrogen peroxide a very interesting

transformation occurs fluid between the layers of either and potassium dichromate

Becomes dark when potassium from dichromate and hydrogen peroxide react in an acidic environment an unstable compound is formed

chromium oxide peroxide that compound decomposes immediately in an aqueous solution and

Gives a middle layer of the liquid this dark color

Chromium oxide peroxide can be stabilized and for that reason the upper layer has a blue color

What country with the flag will these colours belong to. But, the reaction itself is quite colorful

however when conducted these experiments it is worth remembering that the compounds of hexavalent chromium are

But at the same time compounds of trivalent chromium are micro elements in our body such a two-faced is chromium

pure metallic chromium is often included in the

composition of stainless steel that has up to 30% of this metal the fact is that the metal Coromium is very

oxide film that covers the metal the same film of chromium oxide is formed on the surface of stainless steel