Chromium - The HARDEST METAL ON EARTH!
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Published 2017-11-18
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Do not repeat the experiments shown in this video!
So, today I want to tell you about the hardest metal on Earth – chromium. As usual, let's first see where chromium is in the periodic table of chemical elements. Oh, there it is, hiding behind the vanadium in the 6th group.
And yes, I did not deceive you, it is true that chromium has the highest hardness of all metals, based on the Mohs scale that shows the resistance of a mineral to scratching.
Externally, pure chromium is a lustrous white metal that does not tarnish in air. To demonstrate the main feature of chromium, namely its topmost hardness, I will scratch an ordinary silicate glass with it.
As you can see on this chart, the hardness of the glass is much smaller. As usual, you cannot fool physics, chromium easily scratched the surface of the glass, leaving a clearly discernible markings. Although, I think that the hardness of chromium is very much dependent on its purity.
Metallic chromium is obtained from the chromium ore 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. The fact is, even the name of the metal, chromium, comes from the Greek "khroma" meaning color.
This name came to pass due the fact that chromium compounds can have almost all the colors of a rainbow. In a 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, this substance is used as an intermediate compound in the production of chromium metal from ore.
In this compound chromium has an oxidation state of plus six.
By the way, if you mix the potassium dichromate with any reducing agent, for example aluminium powder, and then ignite it, you will see a very violent reaction that will produce particles of chromium metal.
Potassium dichromate is very soluble in water. 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 six, chromium may have a yellow and an 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 its color 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 six.
Now I’m igniting this orange powder and what do we see? Ammonium dichromate started decomposing by itself, forming a dark-green substance – chromium oxide.
All Comments (21)
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i love how smart these people are in chemistry and i always learn from them, thanks
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chemistry sounds soo badass when its explained with a russian accent ;P
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I think the kidney stone I passed last year was the hardest material on earth
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Your videos are getting even more interesting! High quality content. Thanks for sharing.
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I was going to make a sodium hydride joke, but NaH
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That ammonium dychromite reaction was the most satisfying thing I've ever seen... thank you
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I'm an Australian and I bloody love your accent Buddy it's amazing! Easy to understand for me and so fascinatingly different. Iv been trying to learn how to say words like you pronounce them 👌 keep up the amazing shows mate!
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Thanks a lot, your videos makes chemistry easier to understand, greetings from Dominican Republic.
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The hardest metal on earth, and to remove from your computer.
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Hex Chrome 6 (Cr+6) is used in metal finishing of zinc and cadmium electroplating. However it’s part of the RoHS world directive of the 6 chemicals they’re trying to ban for everything man made. Chromium +6 works great to prevent bare steel from rusting but it’s being faded out world wide becasue it causes cancer if injested. They used to coat steel pipes with zinc and then Hex Chrome +6 as the top coat. It leaves a yellow iridescent sheen on the surface of plated steel. In the movie, “Erin Brokovich” staring Julia Roberts, it tells the true story of an entire town in Southern California that suffered greatly with birth defects and cancer becasue hex chrome 6 was used to coat the water pipes of houses. So now in the industry we use Trivalent chromium (Cr +3) on zinc electroplating and it’s not as good a protector as Hex Chrome, but it is safer to handle. ...oh well, so be it.
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Excellently explained. Easy to follow, and marvelously photographed.
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The greatest amount of information I've ever heard in under 10 minutes! EXCELLENT!
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College dropout here! Thanks for making chemistry accessible to us dumbasses through your excellent descriptions!!! Were you my college professor(s), I'd likely have matriculated into an engineering profession; instead I spent 22 years in the Army...
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Chromium in the +3 state forms may colored depending on what it is coordinated to Chrome Alum , KCr(SO4)•12H2O consists of purple cristalls where the chromium is coordinated to six water molecules. If a reductive reaction on K2CrO7 to chromium +3 occurs in water the result is a deep green color as different things are coordinated to the chromium. Many colors are possible with Cr +3 depending on how it is coordinated.
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That was a fun video, thank you Thoisoi2.
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I like your channel. It gets right into the science!
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It’s shit like this that I wish I was born smarter to become a chemist
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If you uploaded this video one day before, I could have won the science quiz!!!!!!!!!!!!!!!
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You made my day with the clip from Особенности национальной охоты XD
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Awesome vid as always. This one didn't show up in my subbed feed, it normally would. Just thought you might wanna know
