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!

Homework Help: PH and mL through pKa+log[A-]/[HA]

  1. Sep 27, 2012 #1
    1. You have a .246 M HNO3 solution. You also have 213mL of a 0.00666M 2,2' -bipyridine. You want a solution with pH 4.19. How man L of .246M HNO3 do you add to the 213mL other stuff?

    2. pH=pKa+log[A-]/[HA] also, pKa of 2,2' -bipyridine is 4.34 I think.

    3. pH=pKa+ log[A-]/[HA]

    (5.96x10^-5mol) / (0.246M)= .0002423L or .2423 mL

    I know that is not the right answer, I'm just not sure what I am doing wrong. Is this the wrong equation for the problem or is there something else I need to do?
  2. jcsd
  3. Sep 28, 2012 #2


    User Avatar

    Staff: Mentor

    First things first - what is your HA and what is your A-?

    Note you have not used volume of the pyridine solution. You are right about using Henderson-Hasselbalch equation, but you need to pay attention to the way you calculate concentrations.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook