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Homework Help: Finding the pH of a buffer solution when a strong acid is added

  1. Feb 12, 2012 #1
    1. The problem statement, all variables and given/known data

    Three milliliters of a 2.0 M solution of HCL are added to 1 liter of buffer solution containing 0.40 moles of the weak acid, propanoic acid (Ka = 1.4 x 10-5) and .50 moles of its conjugate base, sodium propanate.

    1) find the ph of the buffer solution

    2) find the ph when the strong acid is added to the buffer solution

    2. Relevant equations

    Henderson Hasselbach equation: pH = Pka + log( A- / HA)

    3. The attempt at a solution

    1) to find the pKa -log(1.4 x 10-5) = 4.85
    pH = 4.85 + log(.4/.5) = 4.75
    is this correct?

    2) clueless
  2. jcsd
  3. Feb 13, 2012 #2


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    Staff: Mentor

    What happens when you add a strong acid? Is there any reaction taking place? How does it change concentrations of propanate and its conjugate acid?
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