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Homework Help: Rate of Reaction problem

  1. Jan 21, 2010 #1
    1. The problem statement, all variables and given/known data
    Assume that you mixed 20.00 mL of 0.040 M KI with 20.00 mL of 0.060 M (NH4)2SO8, 10.00 mL of 0.00070M Na2S2O3, and a few drops of starch. The point of mixing sets time=0. Calculate the concentrations of the three species KI, (NH4)2S2O8, and Na2S2O3 after mixing but before any reaction has occured. Hint: your calculated [KI] should equal 0.016M.

    2. Relevant equations
    [tex]k= Ae^{-Ea/RT}[/tex]

    3. The attempt at a solution
    I don't really know how to start this problem. How can I calculate concentrations before reactions take place? Any help/hints will be much appreciated.
  2. jcsd
  3. Jan 22, 2010 #2
    Work out the moles of each that have been added, and work out the overall volume of the mixture. The fraction will give you the concentration.
    Ignoring the 'drops' of starch, which you have to do anyway, as there is no volume specified. That equation supplied isn't relevant, as far as I am aware.
    I hope that helps!
  4. Jan 23, 2010 #3


    User Avatar

    Staff: Mentor

    As nobahar wrote - treat it as a simple dilution problem. You know initial concentrations and initial volumes, you can calculate final volume - that's all you need.

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