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Homework Help: How much OH- must be added to achieve desired pH?

  1. May 22, 2008 #1
    1. The problem statement, all variables and given/known data
    Glycine which has a pKa of 9.6 can exist in protonated form (-NH3+) or as the free base (-NH2) because of the reversible equalibrium R-NH3+ <------> R-NH2 + H+.

    How much 5 M KOH must be added to 1.0 L of 0.1 M glycine at pH 9 to bring the pH to exactly 10?

    2. Relevant equations

    3. The attempt at a solution
    I have spent a couple hours trying to figure this out but don't really know where to start. A couple hints might point me in the right direction
  2. jcsd
  3. May 22, 2008 #2


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    Staff: Mentor

    When you add KOH to pH 9 glycine solution you are in fact neutralizing -NH3+.

    Use Henderon-Hasselbalch equation to calculate amount of -NH3+ in solution at pH 9 and 10, then it is a simple stoichiometry.
  4. May 22, 2008 #3
    Thanks Borek, very helpful :).
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