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Homework Help: Phosphate buffer

  1. Mar 29, 2007 #1
    Hi everybody!
    I want to prepare 1000 ml of 0.1M phosphate buffer solution, pH = 7.0. I used Henderson Hasselbach's equation: pH = pka + log [salt]/[acid]. I obtained 0.062 moles of H2PO4- and 0.038 moles of HPO42-. Where I am wrong? Thanks a lot!
    B
     
  2. jcsd
  3. Mar 29, 2007 #2

    chemisttree

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    Show your work. Which pKa did you use? What species did you use for [salt] and [acid]?
     
  4. Mar 29, 2007 #3
    Thanks for replying!

    I used (H2PO4)- ↔H+ + (HPO4)2-
    Ka for this equation is 6.2*10-8, deci pKa = 7.21.
    Salt = (HPO4)2-
    Acid = (H2PO4)-
     
  5. Mar 29, 2007 #4

    chemisttree

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    I get the same...
     
  6. Mar 29, 2007 #5
    So, I did it right! Thanks!
     
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