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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
Namely its topmost hardness
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
Chromium comes from the Greek "chroma"
meaning color
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
The substance is used as an intermediate
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
in an alkaline environment
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
now i'm
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
I'm sorry to disappoint you
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
the resulting chromium oxide is
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
Which under normal
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
Which has another specific smell?
This smell is very
Similar to the smell that can be felt in the morning after a hangover as the ethanol in our body is also
oxidized to acetic aldehyde
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
Next we need diethyl ether
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
however in
Organic solvents such as diethyl ether
Chromium oxide peroxide can be stabilized and for that reason the upper layer has a blue color
I have no idea
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
extremely toxic
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
resistance to the oxidation by airs
Oxygen due to the tiny and very durable
oxide film that covers the metal the same film of chromium oxide is formed on the surface of stainless steel
That protects the metal from further oxidation at the end. We can say set in its pure form
Chromium is a very hard metal true at the same time
Having a huge range of compounds with a variety of colors
you know you know a little bit more about one of the other metals if you would like to support a
Continuous production of science videos like this one. Please support channel on patreon link in the video description
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391 Folder Collection
Wongwl published on January 11, 2018
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