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Buffer Capacity

  1. Apr 4, 2006 #1
    What is the smallest amount of solid NaOH that will exceed the buffer capacity 500mL of a buffer that is 0.4M in acetic acid and 0.15M in NaOAc?

    a)5.69 b)5.16 c) 4.74 d) 4.31 e)3.00 grams

    Since this is a strong base, we only need to deal with the 0.4M of acetic acid.

    so 0.4M *.5L = 0.2moles of NaOH

    that's 8 grams. What am I doing wrong here?
     
  2. jcsd
  3. Apr 4, 2006 #2

    siddharth

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    Homework Helper
    Gold Member

    I think you should read up on what a buffer is.
    http://en.wikipedia.org/wiki/Buffer_solution

    So, can you see why what you did is wrong?
     
  4. Apr 4, 2006 #3
    oops... i think i got the answer... thanks
     
  5. Apr 5, 2006 #4

    Borek

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    Staff: Mentor

    Seems there are different definitions of buffer capacity in use. I was taught buffer capacity is defined as the ratio of the amount of strong base or strong acid added to the change in pH - thus you can't say when it will run out - as it is value that you can calculate for a point (as first derivative, dn/dpH, where n - moles).
     
  6. Apr 8, 2006 #5

    Borek

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    Staff: Mentor

    Buffer capacity definition and some discussion.
     
  7. Apr 5, 2007 #6
    Does anyone know what the answer to that question is? I tried to figure it out but I'm getting enough of a pH change for any of the amount of solid.
     
  8. Apr 8, 2007 #7

    Borek

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    Staff: Mentor

    First of all - what pH change do you expect?
     
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