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Homework Help: Calculating [OH-] from an acid and salt.

  1. Jan 20, 2013 #1
    1. The problem statement, all variables and given/known data
    Calculate the [OH-] concentration in a 0.5 M solution of potassium fluoride (KF). Ka for
    HF is 7.2 × 10−4.

    3. The attempt at a solution
    I know that KF → K+ + F-, therefore having a 1:1 ratio, [F-] = 0.5M
    ,but from here I am unsure what to do with the F- concentration.

    I know that Ka = ([H+][F-])/[HF] and normally I would set up an ICE chart, but I would have too many variables in this case. (Not knowing the concentration of [HF] as well as the "change")
    Last edited: Jan 20, 2013
  2. jcsd
  3. Jan 20, 2013 #2


    User Avatar

    Staff: Mentor

    F- + H2O <-> HF + OH-

    Or, to put it differently - F- is a Bronsted base.
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