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Homework Help: Buffers, pH, and strong base

  1. Oct 27, 2008 #1
    1. The problem statement, all variables and given/known data
    Calculate the pH after 0.030 mol NaOH is added to 1.00 L 0.100 M HC3H5O2 and 0.100 M NaC3H5O2


    2. Relevant equations
    Ka=[H+][A-]/[HA]
    pH=-log([H+]) or 14-pOH=ph


    3. The attempt at a solution
    HC3H5O2 <-> H+ + C3H5O2-
    NaC3H5O2 <-> Na+ + C3H5O2-

    I know that Na+ has no acid/base properties, so I think that this equation is unimportant and I will be focusing on the first equation. I also know Kaeq1=1.3x10-5

    I tried to set up an equilibrium equation, but I'm not sure if I should be completely ignoring the sodium equation.

    1.3x10-5=(x2)/(.100-.030)
    the numerator= [H+][C3H5O2-]

    Any input would be appreciated...
     
  2. jcsd
  3. Oct 27, 2008 #2

    Borek

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    Staff: Mentor

  4. Oct 27, 2008 #3
    Wouldn't that yield
    pH=log(1.3e-5)+(.030/.1-.030) = 4.52? This answer is incorrect. Is there an initial concentration for C3H5O2- that I am missing?
     
  5. Oct 27, 2008 #4

    Borek

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    Staff: Mentor

    Yes.
     
  6. Oct 27, 2008 #5
    oh... duh..
    thanks :-)
     
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