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Author: Subject: Black sugar - What the hell just happened?
cnidocyte
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[*] posted on 3-9-2010 at 12:54
Black sugar - What the hell just happened?


I stupidly didn't do enough research on this one. I read about black sugar and concluded that all I needed to do was mix some H2SO4 with sugar and watch the reaction. I added a bit of acid to a jar with some brown sugar in it and mixed it up a bit but no reaction occured so I concluded I was missing something. I added a bit of NaOH to neutralize the H2SO4 and a few seconds later a violent reaction occured and a fair bit of gas or vapour came out so I got inside since I didn't know what the gas or vapour was. The jars full of black sugar now and theres an unpleasant rubbery smell lingering.

What exactly happened? Did the heat from the dissolution of NaOH start the reaction that would of occured if I had just heated up the H2SO4/sugar mixture or did something else happen there? I used a 98% H2SO4 solution so what was the gas or vapour (it was the colour of water vapour) and what is that rubbery smell?
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psychokinetic
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[*] posted on 3-9-2010 at 13:08


I can't say for sure about the chemistry going on in there, but the rubbery smell is probably something akin to, well, rubber! :D

Petrochemical rubbers are made of carbohydrates, as is the sugar you just tortured.




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watson.fawkes
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[*] posted on 3-9-2010 at 13:12


Quote: Originally posted by cnidocyte  
What exactly happened?
"Post hoc, ergo propter hoc" happened to your mind. Are you really certain that adding NaOH was causative of anything?
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cnidocyte
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[*] posted on 3-9-2010 at 13:52


Quote: Originally posted by watson.fawkes  
Quote: Originally posted by cnidocyte  
What exactly happened?
"Post hoc, ergo propter hoc" happened to your mind. Are you really certain that adding NaOH was causative of anything?


No but a violent reaction occured a few seconds after I added a gram or 2 of NaOH. I didn't even get a chance to mix it in before it started sizzling and the jar started fuming. There is a pile of white, crystalline looking stuff on top of the black sugar though which is probably unreacted NaOH. The NaOH would have instantly started neutralizing the H2SO4 though which I'm guessing is an exothermic reaction so maybe the heat sped up the sugar dehydration.
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denatured
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[*] posted on 3-9-2010 at 13:52


http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA5/MAIN/1ORGANIC/...

http://jchemed.chem.wisc.edu/JCESoft/CCA/CCA5/MAIN/1ORGANIC/...

You have two things that might have accelerated the reaction:
1. heat of dissolution (NaOH + H2O).
2. heat of neutralization (NaOH + H2SO4).

Try it again without adding NaOH and leave it for a while, you should see the same black mass.
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cnidocyte
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[*] posted on 3-9-2010 at 13:54


Quote: Originally posted by denatured  

You have two things that might have accelerated the reaction:
1. heat of dissolution (NaOH + H2O).
2. heat of neutralization (NaOH + H2SO4).

Try it again without adding NaOH and leave it for a while, you should see the same black mass.


Yeah thats what I suspected. Thanks for the links. Yeah I'll try it again without the base. Is this black stuff mainly solid carbon? I just watced this video
http://www.youtube.com/watch?v=pqi50sjJVc0&feature=relat...
I see now whats going on. The gas was mainly water vapour and it doesn't form straight away like I was expecting.

[Edited on 3-9-2010 by cnidocyte]
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[*] posted on 3-9-2010 at 16:50


Quote: Originally posted by cnidocyte  

Yeah thats what I suspected. Thanks for the links. Yeah I'll try it again without the base. Is this black stuff mainly solid carbon?



----------
A little reductionist chemistry

Sucrose (table sugar) is C12H22O11. One could think of
it as C12 (H2O)11. The sulphuric acid sucks up all the H2O
leaving the carbon.


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anotheronebitesthedust
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[*] posted on 4-9-2010 at 01:22


http://en.wikipedia.org/wiki/Passivation

I think someone else posted about how concentrated nitric acid and iron won't react until the acid is diluted. Maybe something similar happens with sulfuric acid.
Quote:

http://en.wikipedia.org/wiki/Nitric_acid
Although chromium (Cr), iron (Fe) and aluminium (Al) readily dissolve in dilute nitric acid, the concentrated acid forms a metal oxide layer that protects the metal from further oxidation, which is called passivation.
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[*] posted on 4-9-2010 at 02:06


I would also suggest using WHITE sugar, since it is purer - in contrast to brown sugar which contains other things than just sucrose.
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cnidocyte
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[*] posted on 4-9-2010 at 09:45


Yeah theres way more contrast with white sugar too. What allotrope is this black sugar? Is it graphite?

BTW I tried this reaction without the NaOH and the sugar turned black but at an incredibly slow pace. I recommend trying this reaction out with NaOH because its fairly impressive. Do it outdoors though, I've never seen so much gas evolve from a reaction at such a rapid pace.

[Edited on 4-9-2010 by cnidocyte]
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[*] posted on 4-9-2010 at 11:13


Try putting a few drops of H2O on the sugar before adding the H2SO4. That usually speeds things up.
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[*] posted on 9-9-2010 at 12:07


Even with strong acid the sugar may take a while to go. Once the reaction starts, it's own heat will exponentially accelerate the rate.

Adding the NaOH? I'm going with the others, you may have bump started the reaction with the heat that will produce.

The rubbery smell is burnt; carbonaceous junk (the acid is dehydrating the sugar to simple carbon compounds, or just plain carbon). The gas was likely steam, probably carrying some sulphuric acid or NaOH up with it.

Repeat the sugar method with sulphuric and leave it for a couple of minutes. Use white sugar and keep the acid in the warm house prior to starting, so it will get moving quicker.

Something looking a lot like a big turd should grow out of the beaker. Like this <------------

Remember that a lot of what your body is made out of is very similar to what's in that beaker prior to the acid going in.

[Edited on 9-9-2010 by peach]




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