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Homework Help: Phosphate buffer calculation

  1. Apr 17, 2010 #1
    1. The problem statement, all variables and given/known data
    To prepare 1M phosphate buffer pH7.8. pKa=7.21. How much molar of Na2HPO4 and NaH2PO4 to be added
    I have no confidence in my answer... Can anyone pls have a check?


    2. Relevant equations
    pH=pKa+lg (base/conjugate acid)


    3. The attempt at a solution
    7.8=7.21 +lg (a/b)
    0.59=lg (a/b)
    a/b=3.89
    a+b=1-----1
    a=1-b -----2
    (1-b)/b=3.89
    b=0.2045 -Na2HPO4
    a=0.7955 -NaH2PO4

    Is my way of doing it correct? Did i forget to calculate other things that i must?
     
    Last edited: Apr 18, 2010
  2. jcsd
  3. Apr 18, 2010 #2

    Borek

    User Avatar

    Staff: Mentor

    Your approach is correct. But:

    OK

    Check your math.

    --
     
  4. Apr 18, 2010 #3
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