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!

The unit of measurement of degree of dissociation ( α ) ?

  1. Mar 16, 2016 #1
    • You have to show your attempts, this is a forum policy. Also, all homework like questions should go to homework forum.
    What's the unit used to measure α ? if α=(Kd/C)0.5 where Kd is the dissociation constant and C is the total concentration of electrolyte .
     
  2. jcsd
  3. Mar 16, 2016 #2
    perhaps ..degree of dissociation refers to the
    amount of solute dissociated into ions or radicals per mole. its denoted by alpha.

    The classical Theory of electrolytic dissociation,is based on the assumption of the incomplete dissociation of the solute,
    characterized by the degree of dissociation α, that is,the fraction of the electrolyte molecules that dissociate.
    for details ; see <http://encyclopedia2.thefreedictionary.com/Electrolytic+Dissociation> [Broken]
     
    Last edited by a moderator: May 7, 2017
  4. Mar 16, 2016 #3

    Borek

    User Avatar

    Staff: Mentor

    Why don't you plug units into the formula and see what you get? What is the unit of the concentration? What is the unit of Kd?
     
  5. Mar 17, 2016 #4
    I've already done that , but before I did so , my teacher had told me it's unit-less , he said that according to our school textbook , according to this idea , concentration is measured in mol/Litre and Kd doesn't have a unit as it's a ratio between two constants , therefore the unit of measuring alpha should be Litre/mol ,which sounds a little bit weird
     
  6. Mar 17, 2016 #5

    Borek

    User Avatar

    Staff: Mentor

    Sure it does. Please write the formula.

    Besides, I just realized your formula for α looks odd.
     
  7. Mar 18, 2016 #6
    I'm sorry but what formula you want me to write ? and what do you mean the formula for alpha looks odd ? thanks .
     
  8. Mar 18, 2016 #7

    Borek

    User Avatar

    Staff: Mentor

    Write the formula for Kd, to see what are Kd units.

    α is just the dissociation percentage (fraction), I don't see how it can be calculated using formula you gave in the opening post.
     
  9. Mar 24, 2016 #8
    If ##\mathbf{AB \leftrightarrow A^+ + B^-}## then ##\mathbf{K_d=\frac{[A^+][B^-]}{[AB]}}##
    then ##\mathbf{K_d=\frac{α^2C}{1-α}}## , and ##\mathbf{1-α\approx1}## therefore ##\mathbf{α=\sqrt{\frac{K_d}{C}}}## where C (concentration) is measured in Mol/litre and ##K_d## is unit-less .
     
  10. Mar 24, 2016 #9

    Borek

    User Avatar

    Staff: Mentor

    I see, that's an approximation only.

    Why do you think Kd is unit-less? You wrote a formula - what does it tell you?
     
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: The unit of measurement of degree of dissociation ( α ) ?
  1. Degree of Dissociation (Replies: 1)

  2. Dissociation energy ? (Replies: 1)

  3. Phenol dissociation (Replies: 1)

Loading...