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Homework Help: CHEMISTRY- another pH question

  1. Apr 12, 2010 #1
    1. The problem statement, all variables and given/known data
    What is the pH of a saturated Zn(OH)2 solution?

    Ksp = 1.2 x 10^-17



    2. Relevant equations

    Ksp = [Zn2+] [OH-]^2

    Zn(OH)2 <----> Zn2+ + 2OH-

    pOH = -log [OH-]

    pH = 14- pOH

    3. The attempt at a solution

    Ksp = 1.2 x 10^-17 = [Zn2+] [OH-]^2

    Zn(OH)2 <----> Zn2+ + 2OH-
    - x +x +2x
    1.2 x 10^-17 = [x][2x]^2 = 4x^3
    x = 1.4 x 10^-6 M
    [OH-] = 2x = 2.8 x 10^-6 M
    pOH = - log 2.8 x 10^-6 = 5.5
    pH = 14 - 5.5 = 8.5

    Again I am learning this on my own and do not have a solution manual to the textbook I am using. So just s quick check would be greatly appricated. Thank you for your time.
     
  2. jcsd
  3. Apr 12, 2010 #2

    Borek

    User Avatar

    Staff: Mentor

    Approach looks OK and final result seems reasonable.

    Note that this is very close to the place were OH- from water dissociation may play an important role.

    --
    methods
     
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