1. Limited time only! Sign up for a free 30min personal 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!

Isoelectronic Point

  1. Feb 9, 2014 #1
    1. The problem statement, all variables and given/known data
    Why must the PI be an average of two PKa's

    2. Relevant equations

    pI = (Pka1 + pKa2)/2

    3. The attempt at a solution
    the pI is the point when the net charge of a compound is zero.

    I dont really know why it must be the average of two pKa's. Please I need help!
  2. jcsd
  3. Feb 9, 2014 #2
    I assume you're mentioning this in the context of biochemistry. What is the pKa of a substance? It's the pH at which half of the molecules are dissociated. If you have a negatively charged ion and a positively charged ion, then at some given pH (that is, the pI) the NET charge is equal to zero. That is, the anion and cation experience equal dissociation rates: the zwitterion or uncharged form may exist in situ, but the (# positive charges) - (# negative charges) = 0. At this pI, there is an equal likelyhood that the anion will exist as there is the cation, and as such, the net charge is zero.
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: Isoelectronic Point
  1. Boiling Points (Replies: 1)

  2. Freezing point (Replies: 2)