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Homework Help: Ka estimate

  1. Nov 4, 2008 #1
    1. The problem statement, all variables and given/known data
    Estimate the Ka the using the assumption that the color change can be seen by our eyes when [ln-]/[Hln] = 1/10
    to see the acid form or [ln-]/[Hln] = 10/1 to see the color associated with the base.
    Use these numbers with your measured [H+] to calculate a Ka for each indicator you measured.

    2. Relevant equations
    acid-base base-acid H+
    Phenolphthalein 8.7 7.4 8.91E-09

    I got the hydronium concentration by taking taking the average of the ph values and doing 10^-ph. How do i get the ka estimates?

    Do i set up the equation like this: ka = 1/[H+] or something like this?
     
  2. jcsd
  3. Nov 4, 2008 #2

    Borek

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    Staff: Mentor

    Describe the experiment that you did. I am almost sure you have not posted all information that you have.
     
    Last edited: Nov 4, 2008
  4. Nov 4, 2008 #3
    am49vo.jpg
     
  5. Nov 4, 2008 #4

    Borek

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    Staff: Mentor

  6. Nov 4, 2008 #5
    ya i know that the phs are wrong. The bromophenol blue was really off. When calculating the H+ concentration, i only used 4.2, not 9.3.
     
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