PH/Titration Question

  1. 1. The problem statement, all variables and given/known data
    Calculate the pH at the equivalence point for the titration of 0.20 M NH3 with 0.20 M HCl? Kb of ammonia is 1.8e-5

    This is just a old test I am going over, I managed to get a pH of 4.98. but that is not right the right answer is 5.12 and I cant figure out why. I would assume you could use the henderson equation but I only get 4.98 which is wrong.

    Any help?
     
  2. jcsd
  3. Borek

    Staff: Mentor

  4. Even if I did not use HH equation I am getting the wrong answer.
     
  5. Borek

    Staff: Mentor

    So show details of your work, hard to say what you did wrong not knowing what you did.
     
  6. k.... using ICE table below:

    [​IMG]
     
  7. Borek

    Staff: Mentor

    Please reread my very first post in this thread. Every word of it.
     
  8. I did and didn not use the HH eq, not do i understand what you mean by dilution.

    I also read link, and this is onlything really useful that I understood but still does not explain what I am doing wrong:
    In the case of titration of weak base with strong acid, situation is very similar - pH at the equivalence point is determined by the weak base salt hydrolysis. Thus we need pKa of conjugated acid to calculate H+ and pH. Check lecture and cheat sheet mentioned above for details.

    It would be great if you told me what I am doing wrong...
     
  9. Borek

    Staff: Mentor

    Try here: dilution effects. Generally speaking, you have mixed two solutions, concentrations have changed as the final volume differs from the initial for each reagent.
     
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