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Dextrose-based momentum-sensitive mixture

  • #1
O hai, PF
So, again, I come in the seek of help. I am usually good for my level on Chemistry, but this question was too hard for me.
In the lab, we added 0.8 g of KOH and 30 ml of H2O. Then, 1g of dextrose and methylene blue.
Final results were a liquid blue mixture. Thing is, when that thing is shaked, it changed to a transparent color. After resting, it became blue again. If shaked again, it would become transparent, then, after resting, blue again and ad infinitum.
Just why did this happen? What kind of reaction was happening?
As the final data I can give, the lab report says we could also have used glucose instead of dextrose. We were, also, studying redox reactions, I'd guess this one was redox, but what was it?

Was it K2O reacting to the dextrose? Was O2 changing its oxidation state by entering and leaving the compund depending on the momentum?
 
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Answers and Replies

  • #2
chemisttree
Science Advisor
Homework Helper
Gold Member
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The dextrose (glucose by another name) is an aldehyde that is oxidized by methylene blue. The methylene blue is reduced to leucomethylene blue (colorless) as it oxidizes the dextrose to .... what? The reaction stops there except you can do something to regenerate the methylene blue. What agent might be responsible for regenerating methylene blue from the colorless (actually light yellow, BTW) leucomethylene blue? How does shaking accelerate that reaction? Hint: it has nothing to do with momentum.
 
  • #3
After some accidental searching, I found a name. Gluconic acid that can transform to sodium gluconate. I don't have the slightest idea of how those compounds are, but they do some weird magic.
No, no that kind of magic. I mean MAGIC, in capital and everything.
Now...what? I'm sure oxygen is part of the reaction, yet I'm clueless about how it is relevant.
 
  • #4
Borek
Mentor
28,303
2,687
You are right about oxygen - shaking the solution introduces the oxygen (which otherwise is present only close to the surface), allowing reactions to start.
 

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