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Homework Help: How do they react?

  1. Jan 27, 2007 #1
    How does acidified potassium dichromate, K2Cr2O7 react with ethanol, C2H6O ? What is the resultant product?

    And as an aside question what is the difference between acidified potassium dichromate and potassium dichromate?
  2. jcsd
  3. Jan 27, 2007 #2


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    pivoxa, this is a standard textbook problem and belongs in the Homework section.

    Acidified dichromate is a solution of dicromate mixed with a suitable dilute acid. Acidification increases the oxidation potential of the dichromate ion.
  4. Jan 28, 2007 #3


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  5. Jan 28, 2007 #4
    I've seen this site but what are the half reactions?

    For chromium, it's (Cr2O7)2- + 14H+ + 6e- -> 2Cr3+ + 7H2O

    For ethanol on the surface it looks like C2H5OH + O2 -> CH3COOOH + H2O
    but where is the electron in this half reaction?
    Last edited: Jan 28, 2007
  6. Jan 29, 2007 #5


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    C2H5OH + H2O + ---> CH3COOH + (H+) + (e-)
    Balance and premultiply as required to complete.

    Alternatively, to your above second reaction, add the third reaction:
    H2O ---> O2 + (H+) + (e-) and balance the lot of them.
  7. Jan 30, 2007 #6
    The two half reactions are
    ((Cr2O7)2- + 14H+ + 6e- -> 2Cr3+ + 7H2O ) * 2
    C2H5OH + H2O -> CH3COOH + 4(H+) + 4(e-) * 3

    Net reaction is:
    3C2H5OH + 2(Cr2O7)2- + 16H+ --> 3CH3COOH + 4Cr3+ + 11H2O

    The trick was in determing that the product of C2H5OH is CH3COOH. The rest can be done by balancing water, H+ and e-. Are there ways of working out which product will form or do people usually look at tables. FOr predicting complex reactions is the best way to look up in a table? If so is there a large table on the web? I have seen ones in the textbook but many reactions seem to be missing from them.
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