Fantasma4500
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Chemical cameleon end results?
a friend asked me what the end results for the infamous chemical cameleon is, those who havent done or seen the reaction yet: you dissolve a small
amount of KMnO4 in water, then add NaOH and sugar to the water
it will then change colours due to the ions of manganate, it will change colours around 5 times, ending up as red-yellowish or lightly brown
once searched around for the equation but i couldnt really find it
i guess the final product is MnO2, the others must be KOH..?
KMnO4 + NaOH + C12H22O11 > KOH + MnO2
but there must be more than this..? anybody have an idea?
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blogfast25
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The overall reaction is slow and is an oxidation reaction of sucrose (white sugar) with KMnO4, in alkaline conditions. Because of the slow rate, you
see the Mn going from oxidation state VII (purple, permanganate), to VI (green, manganate) to IV (brownish, manganese dioxide). It's a nice
demonstration of the gradual nature of such an oxidation and the colours of three of the main oxidation states of Mn. In acid conditions the whole
thing would go down to Mn II (and much faster, I believe).
The oxidation product of the sucrose could be various things. With concentrated nitric acid sucrose can be oxidised to oxalic acid. With dry
permanganate it can quite violently be oxidised to CO2. So it depends rather on conditions of temperature, pH and concentration what it is that you
obtain as an oxidation product.
Pyrolusite (the mineral form of MnO2) was once also known as 'chameleon stone' because when you heat it with KOH and KNO3 it oxidises to green K2MnO4
(potassium manganate)
[Edited on 14-4-2013 by blogfast25]
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woelen
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In this webpage I describe this reaction in quite some detail:
http://woelen.homescience.net/science/chem/exps/chameleon/in...
It indeed is a nice experiment.
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blogfast25
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Woelen, I note that you're also reluctant to state what the precise end-product (apart from MnO2) actually is.  Lovely photos, BTW!
[Edited on 14-4-2013 by blogfast25]
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MrHomeScientist
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I wrote a page about this reaction on the site for the educational outreach program I run: http://www.sciencebrothers.org/the-chemical-chameleon/
It's the first result when you google 'chemical chameleon'! 
Down in the comments, I presented what I thought might be happening, after a lot of searching. There's surprisingly little information on what the
actual reaction is. I came up with 'pyruvic acid' (CH3COCOOH) as the endpoint for the glucose.
4 KMnO4 + 3 C6H12O6 == 4 MnO2 + 6 C3H4O3 + 4 KOH + 4 H2O
Although, now that I look at it again, the acid would probably react with the KOH to form potassium pyruvate and more water.
Another commenter posted this as a possible equation:
2 KMnO4(aq) + 2 NaOH(aq) + 2 C6H12O6(aq) = 2 C6H11O7Na(aq) + K2MnO4(aq) + MnO2(aq) + 2 H2O(l)
Although I doubt that is correct, because the final solution is completely clear once all the MnO2 settles out. It's also definitely a solid, not
aqueous.
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blogfast25
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Quote: Originally posted by MrHomeScientist  | I came up with 'pyruvic acid' (CH3COCOOH) as the endpoint for the glucose.
4 KMnO4 + 3 C6H12O6 == 4 MnO2 + 6 C3H4O3 + 4 KOH + 4 H2O
Although, now that I look at it again, the acid would probably react with the KOH to form potassium pyruvate and more water.
Another commenter posted this as a possible equation:
2 KMnO4(aq) + 2 NaOH(aq) + 2 C6H12O6(aq) = 2 C6H11O7Na(aq) + K2MnO4(aq) + MnO2(aq) + 2 H2O(l)
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Pyruvic acid was the one I also thought of when considering oxidation products of sucrose/glucose by Chamelon, because at least it appears in the
Krebs Cycle. But definitive proof that Chameleon makes pyruvate is unavailable.
What's "C6H11O7Na" supposed to be known as when it's sitting alone in a jar?
Structurally a linear [6 carbons in series] structure like (CH2OH)(CHOH)4COONa would fit the overall empirical formula of
"C6H11O7Na" and be the salt of a carboxylic acid to boot but I've no idea whether a compound with that structure actually exists. Intriguing...
Having a Google #1 on 'chameleon reaction' is 'kewl'!
[Edited on 15-4-2013 by blogfast25]
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woelen
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Yes, I think that you simply cannot specify precisely what the end product
of oxidation of sugar will be. The first stage almost certainly will be oxidation of one of the hydroxyl groups to a ketone-like structure, but this
can occur at many places in the molecule and after that first stage there may be numerous other reactions. Especially in this situation this is the
case, because the sugar is present in LARGE excess, so only a few hydroxyl groups are oxidized and I expect that the percentage of sugar molecules
with two oxidized hydroxyl groups will be very small.
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12AX7
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chemi-chemi-chemi-chemi-chemi-chemi-chameleon.
Sorry...wasted post...
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Fantasma4500
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| Quote: Originally posted by blogfast25 | The overall reaction is slow and is an oxidation reaction of sucrose (white sugar) with KMnO4, in alkaline conditions. Because of the slow rate, you
see the Mn going from oxidation state VII (purple, permanganate), to VI (green, manganate) to IV (brownish, manganese dioxide). It's a nice
demonstration of the gradual nature of such an oxidation and the colours of three of the main oxidation states of Mn. In acid conditions the whole
thing would go down to Mn II (and much faster, I believe).
The oxidation product of the sucrose could be various things. With concentrated nitric acid sucrose can be oxidised to oxalic acid. With dry
permanganate it can quite violently be oxidised to CO2. So it depends rather on conditions of temperature, pH and concentration what it is that you
obtain as an oxidation product.
Pyrolusite (the mineral form of MnO2) was once also known as 'chameleon stone' because when you heat it with KOH and KNO3 it oxidises to green K2MnO4
(potassium manganate)
[Edited on 14-4-2013 by blogfast25] |
haha.. found in an old book under how to make KMnO4 about the MnO2, got told that its not possible to make KMnO4 by this route in small amounts tho..
another interesting thing i have tried was taking a saturated solution of NaOH and sugar (random amounts..) then dumping in small granules of KMnO4,
it rapidly undergoes these colour states in the trails of the KMnO4 (:
but yes, i was very confused over what all the reaction products could be..
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Fantasma4500
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would be a spamstorm to reply to all of you.. very interesting.. i knew there was some more complex chemistry behind this, and when it starts
involving organic then im not really able to figure it out.. didnt even know there was anything called pyruvic acid (:
also blogfast
''Having a Google #1 on 'chameleon reaction' is 'kewl'!''
got to think of that when you type my first name on google it automatically suggests my full name 
i have no clue why tho.. must of been alot of searches for me somehow, very offtopic i know, sorry (:
the thing about MnO2 with KOH and KNO3 inspires me slightly to trying to make K2MnO4 by heating it.. ill try several different methods..
IIRC its also possible to produce KMnO4 by leading CO2 into the solution to react, i was more into this whole thing with KMnO4 longer time back.. then
i should be able to confirm if i formed permanganate with the cameleon reaction..
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