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Blue Bottle Demostration

  1. May 18, 2006 #1
    I'm trying to finish a lab report on the Blue Bottle Demostration where glucose is added to a solution of NaOH. Then Indigo carmine is added so the solution would go from red to yellow to green (My teacher called it the stop light reaction :D)
    I need to figure out why does the process eventually stop.
    Here is what I think:
    Since O2 in the flask is what re-oxidizes the indigo carmine to reform the initial colour at equilibrium, with out O2, the reaction will eventually stop.
    My question is, what happened to the O2 that oxidizes the indigo carmine? does it just stay there?
     
  2. jcsd
  3. May 19, 2006 #2

    GCT

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  4. May 21, 2006 #3
    What I meant was that when we did the lab in class, when we shook the solution very vigorously, the solution turned blue and never turned back. If all O2 oxidized are then reduced, why did the reaction get stuck?
    One more question:
    I read on the internet that indigo carmine was oxidized twice, once to give the red colour, and once more to give the green colour. How?
    Thanks!
     
  5. May 21, 2006 #4

    GCT

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    I'm not too familiar with this lab, but the reaction with glucose is the first oxidation/reduction reaction with the indicator, the next reaction involves the indicator with oxygen gas, that is the electrons are allocated to the oxygen. I'm not quite sure how reversible this particular oxidation/reduction reaction is. You should access the reaction products for this second reaction.

    I'm guessing that the redox reaction in this case are successive, remember that two electrons are involved in the reaction.
     
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