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Homework Help: Stoichiometry of a RedOx Reaction

  1. Oct 6, 2007 #1
    1. Oxalic acid, H2C2O4, reacts with dichromate ion, in acidic solution to produce carbon dioxide and chromium(III) ion.
    If exactly 50.0 mL of an oxalic acid solution is required to react completely with 25.0 mL of a 0.0100 M dichromate solution, what is the molarity of the oxalic acid solution?

    2. Molarity = Moles/Lsolution

    3. well the equation i got was
    H2C2O4 + CrO7 (2-)---> Cr (3+) + CO2

    I used oxidation method to balance it to

    9H2C2O4 + CrO7 ---> Cr + 7H2O + 4H + 18CO2

    then i found moles of CrO7

    molarity x L solution = 0.01 x (25/1000) = 0.00025 mol CrO7

    then moles of H2C2O4 = 0.00025 mol CrO7 x 9 moles/1 mole

    = 0.00225 moles H2C2O4

    using this i divide by L solution to get molarity?

    M = 0.00225 / (50/1000)

    =0.045 M

    But according to my online assignment i put that in and its WRONG :(

    Maybe i balanced incorrectly or im doing something else wrong
    plz help!!

  2. jcsd
  3. Oct 6, 2007 #2
    never mind i found my mistake i was using

    CrO7 but obviously it is Cr2O7 :D::D:D thanks !
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