1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Henderson Hasselbalch Buffers and Volumes

  1. Jan 27, 2015 #1
    1. The problem statement, all variables and given/known data

    You have 725 mL of an 0.55 acetic acid solution. What volume (V) of 1.30 M NaOH solution must you add in order to prepare an acetate buffer of pH = 4.99? ( The pKa of acetic acid is 4.76.)


    2. Relevant equations

    pH = pKa + log A/HA

    Ratio of A- to HA = 10^(pH-pKA)



    3. The attempt at a solution

    - pH = pKa + log A/HA
    - Ratio A/HA = 10^(pH-pKA) = 10^(4.99-4.76) = 1.70
    - Mols of acid = 0.725 mL * 0.55 M = 0.3988 mM
    - HA = (0.3988 - 1.30 * V) / (0.725 + V)
    - A- = (1.30 * V) / (0.725 + V)
    - A-/HA = (1.30 * V) / (0.725 + V) = 0.3988 = (1.30 * V) / (0.725 + V)

    It has been a while since i've had general chemistry, and now i'm taking biochemistry and need to review acids, buffers, pH, pKa, molarity and volumes. I get to the last step and from here I completely forget what to do. Any help/hints would be appreciated.
     
  2. jcsd
  3. Jan 27, 2015 #2

    Borek

    User Avatar

    Staff: Mentor

    OK

    OK

    Yes and no - watch your units.

    OK

    OK

    No. But the mistake has nothing to do with the chemistry, just check your algebra. You started right with the A-/HA ratio, but instead of plugging correct formulas/numbers (which you correctly calculated earlier) you did something strange. Plug them as it should be done and solve for V, that's all.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted