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Today's element is manganese, which is designated by the symbol Mn and the atomic number 25. This is yet another one in that seemingly endless parade of transition metals that are a boring shiny silver colour in its elemental state (pictured; image by Tomihahndorf [Creative Commons Attribution-Share Alike 3.0 Unported license]). But like its sister transition metals, chromium and vanadium, when manganese is found in minerals, it shows a stunning array of beautiful colours that vary as its oxidation state changes.
Amazingly (to me), our friends in the University of Nottingham's chemistry department mentioned potassium permanganate without also mentioning its gorgeous purple colour (sigh!). So let me show you some kitchen science that demonstrates the changing oxidation state in manganese, starting with purple:
According to the videographer, here is what he did: "The clear solution at the beginning is made up by adding 1/2 a sugar cube and about 10-12 pellets of sodium hydroxide in about 120-150 ml of water. To this, a very dilute solution of potassium permanganate is added."
As you can see in the video, the potassium permanganate [Manganese 7+ (Mn VII)] was a lovely purple colour, but the colour changed to a orangish-brown colour [Manganese 3+ (Mn III)] after a few minutes. This is due to manganese's falling oxidation state.
Of the many oxidation states that manganese can adopt, the most stable is +2, and predictably, many manganese(II) compounds are known, such as manganese(II) chloride (MnCl2) -- which is pale pink in colour. 
This reminds me to show you my pink salt. Because I needed some salt, I purchased 200 grams of some rather lovely "Himalaya salz" last weekend at a local open-air market. This salt (pictured) looks like it has at least some MnCl2 in it because it is definitely pink. But it's not pure pink: as you can see from the photograph, it is comprised of large crystals that range in colour from white to dark orange, although most crystals are pale pink. Which leads me to point out that manganese in the +2 oxidation state -- and only in the +2 state -- is an essential trace mineral for all living things, since all other oxidation states of manganese are toxic.
The +2 oxidation state is also seen in the beautiful mineral rhodochrosite, (manganese(II) carbonate):
Rhodochrosite, from the Sweet Home Mine, Colorado, private collection.
Image: Eric Hunt, 21 October 2006 (Creative Commons Attribution-Share Alike 2.5 Generic license.)
OK, here's one last story about manganese. When I was a wee one, I was an avid coin collector, and spent many hours sorting through $10 bags of loose pennies and nickels purchased from the bank. One day, I was especially thrilled to discover a very old "wartime nickel" that was still in common circulation. Upon finding this rare (and unfortunately battered) coin, I learned a bit about the American war effort. I learned that nickels (five cent coins) has always been made from an alloy of 75% copper and 25% nickel -- hence their common name. But there was a shortage of nickel during WWII, so it was substituted with silver and manganese between 1942 and 1945, so those nickel coins were composed of an alloy of 56% copper, 35% silver and 9% manganese. (Despite these coins' lack of nickel, I am told they were still referred to as "nickels".)
Video journalist Brady Haran is the man with the camera and the University of Nottingham is the place with the scientists. You can follow Brady on twitter @periodicvideos and the University of Nottingham on twitter @UniNottingham
You've already met these elements:
Chromium: Cr, atomic number 24
Vanadium: V, atomic number 23
Titanium: Ti, atomic number 22
Scandium: Sc, atomic number 21
Calcium: Ca, atomic number 20
Potassium: K, atomic number 19
Argon: Ar, atomic number 18
Chlorine: Cl, atomic number 17
Sulfur: S, atomic number 16
Phosphorus: P, atomic number 15
Silicon: Si, atomic number 14
Aluminium: Al, atomic number 13
Magnesium: Mg, atomic number 12
Sodium: Na, atomic number 11
Neon: Ne, atomic number 10
Fluorine: F, atomic number 9
Oxygen: O, atomic number 8
Nitrogen: N, atomic number 7
Carbon: C, atomic number 6
Boron: B, atomic number 5
Beryllium: Be, atomic number 4
Lithium: Li, atomic number 3
Helium: He, atomic number 2
Hydrogen: H, atomic number 1
Here's a wonderful interactive Periodic Table of the Elements that is just really really fun to play with!
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