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Author: Subject: Weird outcome after sucrose dehydration
Hendrik
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[*] posted on 28-8-2018 at 06:48
Weird outcome after sucrose dehydration


A month ago, I performed the very well known sucrose dehydration using concentrated (98%) sulfuric acid in order to obtain some carbon. I worked with small quantities, in a 50ml beaker. I filled it partially with table sugar and poured 3 to 5 drops of sulfuric acid with a pipette. The reaction started immediately and the sugar started to turn to a yellowish orange. I left the reaction aside in a well ventilated area in order to avoid breathing the SO2 that could have possibly been formed and waited until I noticed the sugar turning black. It seemed that the quantity of H2SO4 used was too low, because, even after 12 hours, the beaker contained a layer of completely black carbon and a layer of untouched sugar on top of it. The dehydration was complete, but I decided to carry on with the following steps. I thought that the best way to separate the two would be to dissolve the remaining sugar in distilled water while the carbon would precipitate out, as it will not dissolve at all. While trying to dissolve everything, the solution became black with an orange tint, totally different from the colorless solution I was expecting. I performed a filtration afterwards and managed to recover some of the carbon. In the meantime, I left the solution to settle, thinking it may be black because of the very fine particles of carbon that were left in suspension. A day had passed, and nothing changed.

A couple of weeks later, I performed another experiment with the weird solution. I took a very small quantity with a pipette and placed it on a hotplate in a very well ventilated area. No steam was generated, but small explosions occured in the beaker I held the solution in, leading to the formation of a white precipitate. After taking the beaker away from the hotplate, stirring the solution would lead to the dissolution of the white precipitate. I even placed it in a freezer (which is not used for food) thinking that would change something, but the solution remained untouched. I have to add I used only distilled water (not tap water) and, even after a month, absolutely no change had occured.

Being afraid of what have I created, I thought about neutralizing the sulfuric acid that was left in the beaker with a concentrated solution of NaOH. I used an excess. Eventually, the beaker contained NaOH, Na2SO4, H2O and the very weird orange-ish black compound that was left in solution.

I know this post is extremely long, but I have a lot of questions regarding this experiment. I know some of you may think it was a stupid experiment, but what actually happened? Did I create a caramel like compound or a soluble sulfonated compound? What are the health risks posed by that black solution? How can I safely dispose of it? Unfortunately, I do not have any photos. Any help would be greatly appreciated.

[Edited on 28-8-2018 by Hendrik]
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Deathunter88
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[*] posted on 28-8-2018 at 07:15


First of all, you added no where near enough sulfuric acid. All of the sugar needs to be saturated for there to be full dehydration. Secondly, as you suspect, the orange solution is just caramelized sugar from the heat of the reaction. There is nothing to be afraid of, and the solution can be disposed of down the drain.
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Sulaiman
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[*] posted on 28-8-2018 at 07:19
as above













so below
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Hendrik
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[*] posted on 28-8-2018 at 07:20


Thank you! It had a caramel like smell, but I wasn't sure about it. I knew there was not enough H2SO4, the carbon should have formed a snake-like shape and come out of the beaker. Now I know what am I supposed to do.
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