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A tough question

  1. Aug 20, 2004 #1

    chem_tr

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    I wanted to share a good question with you. It uses your redox chemistry skills as well as theoretical atomic valance calculation of organic substances. However, nobody managed to solve this problem as it is sufficiently time-consuming and somewhat difficult.

    Write the full-balanced equation of potassium sodium tartrate (KNaC4H4O6; see the attachment) with potassium permanganate in the presence of nitric acid. Note that the orientations of alcoholic OH groups are not important in this question.

    Hint: I can give a reaction of oxalic acid (HOOC-COOH) in this way:

    5*[C(3+) ---> C(4+) + e(-)]
    Mn(7+) + 5e(-) ---> Mn(2+)
    -----------------------------------------------
    5C(3+) + Mn(7+) ---> 5C(4+) + Mn(2+)
    10C(3+) + 2Mn(7+)---> 10C(4+) + 2Mn(2+)

    5 H2C2O4 + 2 KMnO4 + 6 HCl ---> 10 CO2 + 2 MnCl2 + 2 KCl + 8 H2O

    Hint2: Note that tartrate contains two kinds of C atoms; alcoholic and carboxylic, so two different sets of redox chemistry is involved altogether.

    If you have enough time to deal with a challenging question, give it a try.

    Regards
    chem_tr
     
  2. jcsd
  3. Aug 21, 2004 #2

    GCT

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  4. Aug 22, 2004 #3

    chem_tr

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    You are not wrong, but one of my teachers told other students that the exact valence of carbons are not clear and therefore an average value may be proposed for several years, and I tried hard to determine if a valid valence is present.

    Since the time I solved that puzzle-like question, I am very comfortable with redox-chemistry questions; this is one of the most difficult ones. So if anybody has a difficulty with redox chemistry, it may be useful to make an attempt to solve it.

    Regards
    chem_tr
     
  5. Aug 22, 2004 #4
    What is the solvent? Water? Some alcohol?
    What is the function of the Nitric Acid?
    Proton source? Oxidizer?
    What is its molar concentration?
     
  6. Aug 23, 2004 #5

    chem_tr

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    thanks for your interest

    Hello,

    As you see the reaction below, our assumption is qualitative, so the choice of solvent, type of acid, etc. is not very important:

    5 H2C2O4 + 2 KMnO4 + 6 HCl ---> 10 CO2 + 2 MnCl2 + 2 KCl + 8 H2O

    But you are right of course, we may try to solve this question in terms of quantitative basis; tartrate can be a good primer standard for determining permanganate factor. If you want to find the factor (correct concentration) of a permanganate solution with tartrate, you must write the full balanced equation for correct calculation.

    So let's say this question has nothing to do with molar concentrations and even the type of acid.

    The solvent should be an aqueous type because alcohol is readily oxidized by permanganate to give acetaldehyde and even acetic acid; therefore should not be used here. Nitric acid is only proton source in our example;permanganate is the only oxidizer in this question. As an acid, you may use HCl, HClO4, or H2SO4. You will obtain manganese(II)nitrate, potassium and sodium nitrate, etc. in the resulting solution if you use nitric acid.

    Regards,
    chem_tr
     
    Last edited: Aug 23, 2004
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