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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

  • also

  • 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

  • experiment

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

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クロム - 地球上で最も困難な金属 (Chromium - The HARDEST METAL ON EARTH!)

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    Wongwl に公開 2021 年 01 月 14 日
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