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[Chemistry] Rate Law

  1. Feb 25, 2012 #1
    The problem statement, all variables and given/known data
    So I'm doing a lab report on the reaction of food dye with bleach. I have a couple of questions:

    1) What's the difference between pseudo rate constant and rate constant?? (i.e. k' vs. k)

    2) How do I write the rate law for this reaction? I graphed the data and found the reaction order with respect to dye to be 1 and then comparing the changes in k' with respect to the changes in bleach concentrations revealed that the order with respect to bleach was also 1. The pseudo rate constant was 0.1669 (the average slope of all the trials).

    How do I go about writing the rate law? In the explanation it says that the rate law simplifies to Rate = k'[D]^m (where D is the dye) because there is a large excess of bleach present.

    The attempt at a solution

    I think the rate law should be Rate = k[D][OCN-]

    But I'm not sure if the pseudo rate constant can be just substituted as k. and the partial orders for each should be 1 because that's what I found the orders with respect to Dye and OCN ions. Is that correct?
  2. jcsd
  3. Feb 29, 2012 #2
    I have a similar inquiry in which I was able to find the order of the reactants and want to plug them into the rate law formula, but don't know how to eliminate the "prime" aspect of k' to just get the value of k alone.

    Anyone out there have a suggestion?
  4. Mar 1, 2012 #3


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    Staff: Mentor

    Do you know what a pseudo rate constant is?
  5. Mar 2, 2012 #4
    I do not. Although I think I may have answered my own question. :)
  6. Mar 2, 2012 #5


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    Staff: Mentor

    If you don't know what it is, there is no way to solve the problem. Unless you just played with the numbers till the result fit the key - but this is hardly "solving".
  7. Mar 3, 2012 #6
    nvm, I got the answer by reading more of my textbook :P
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