LanthanumK
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Manganese(II) chloride color change
I dissolved manganese(IV) oxide in HCl once and it produced a liquid which was almost colorless after several filtrations. After concentration, it
appeared pale pink, so I dried it to produce pink crystals. After a few months, these crystals have absorbed water, making them slushy, and they also
seem to have lost their color. Now they are a very light tan-pink. Why would MnCl2 change colors? The lighting is the same although the background
changed.
 
[Edited on 23-9-2011 by LanthanumK]
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Arthur Dent
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@LanthanumK : Hah, seems you and I have performed similar experiments!
Here are two different sources of Manganese Chloride:
The MnCl<sub>2</sub> at the left comes from carbon zinc battery crud mixed with conc. HCl and was quite contaminated with iron impurities,
because the solution was tea-colored. After using the Iron Hydroxide trick, I obtained a light pink colored solution that I slowy dessicated over a
few months under anhydrous Calcium Cnloride. You can see the resulting beautiful pink crystal lattice in the remaining yellowish solution.
The MnCl<sub>2</sub> at the right took much less time to prepare, I took some pottery-grade Manganese Carbonate and dissolved it in conc.
HCl and got again a very dark brown solution. I decided to boil off this solution thinking that Ferric Chloride tends to vaporize when strongly
heated, and the solution did indeed turn from dark brown to a light straw yellow to nearly colorless. When it started to form a thin skin on top of
the boiling solution, I stopped the heat and the remaining stuff rapidly coagulated into the very familiar "bubble gum-like" compound. This
MnCl<sub>2</sub> is still very acidic and smells very much of Cl and HCl... I could in theory take this stuff and redissolve it in water
to recrystallize it into a cleaner, less HCl contaminated compound...
I am surprised by the "light tan-pink" color you have, could it be that some of your MnCl<sub>2</sub> is slowly oxidizing, turning to
Oxide/Hydroxide/Carbonate? or could it be some iron impurities showing up?
Robert
[Edited on 23-9-2011 by Arthur Dent]
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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LanthanumK
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It was pink initially but then changed color. I don't think that it is manganese(III) as an oxidation product because manganese(III) is very dark but
the second picture is almost colorless. I used hot air to dry off the MnCl2 instead of a dessicator and the result (Picture 1) was very similar to
your initial result on the left side. The result after a few months (Picture 2) looks like the right side, although it is quite slushy.
Does manganese(II) form any chloride coordination complexes that are more or less pink than the aqua ion? I'm not sure what else would explain the two
different colors of MnCl2 * x H2O and their seeming interchangeability.
hibernating...
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