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Homework Help: PH of buffer solution

  1. May 26, 2008 #1
    [SOLVED] pH of buffer solution

    1. The problem statement, all variables and given/known data

    Calculate the pH of a solution made by mixing 750 mL 1.00 M NH4+Cl and 250 mL 1.00 M NaOH

    3. The attempt at a solution

    NH4+ will react with H2O to form NH3 and H2O+. If my calculations are correct, [H+] after the reaction will be 2.07E-5.

    Then H+ will react with OH-. But since there's almost no H+ compared to NO-, this reaction is irrelevant. The pOH is therefore

    pOH = -log [0.25], and the pH is 13.4

    which is wrong. What's my mistake(s)?
     
  2. jcsd
  3. May 27, 2008 #2

    Borek

    User Avatar

    Staff: Mentor

    You should use Henderson-Hasselbalch equation. Your approach neglects shifting of the NH4+ dissociation equilibrium to the right with H+ neutralization.
     
    Last edited: May 27, 2008
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