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!

Phosphate buffer and pH

  1. Oct 14, 2016 #1
    1. The problem statement, all variables and given/known data
    Phosphate, present to an extent of 0.01 M, is one of the main buffers in blood plasma, whose pH is 7.45. Would phosphate be as useful if the plasma pH were 8.5?

    2. Relevant equations
    pH = pKa+log[A/HA]
    Ka1 = 7.11x10^-3 pka1= 2.148
    Ka2=6.34x10^-8 pka2= 7.198
    Ka3 = 4.22x10^-13 pka3=12.375
    3. The attempt at a solution
    Since the pH would still be between pka2 and pka3 so the phosphate would not gain or lose a hydrogen because of that change and the henderson-hasselbalch equation would still use the same pka. Does this mean it would be just as effective at pH 8.5 or am I missing something?
     
  2. jcsd
  3. Oct 14, 2016 #2

    Borek

    User Avatar

    Staff: Mentor

  4. Oct 14, 2016 #3
  5. Oct 14, 2016 #4

    Borek

    User Avatar

    Staff: Mentor

    You don't have to follow the derivation, but part of the text on that page contains exactly information that you need. Scroll down to the plot and the explanation.
     
  6. Oct 14, 2016 #5
    Okay so that phosphate wouldn't be as good of a buffer at a higher pH because it's greater than the pKa2? 8.5 is closer to pKa3 but since its ka3 is so much smaller than Ka2 that dissociation/association would be much lower.
     
  7. Oct 15, 2016 #6

    Borek

    User Avatar

    Staff: Mentor

    I feel like you are still missing the point. How effective a buffer is depends on how far pH is from the respective pKa value. 7.45 is quite close to 7.2.
     
  8. Oct 15, 2016 #7

    epenguin

    User Avatar
    Homework Helper
    Gold Member

    You must have seen the titration curve for a weak acid or base. Sketch or look up what it looks like.
    You might have to turn it sideways for best understanding.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Phosphate buffer and pH
  1. Phosphate Buffers (Replies: 5)

  2. Phosphate buffer (Replies: 4)

  3. PH and buffers (Replies: 8)

Loading...