Calculating [OH-] from an acid and salt.

[Bound]

Homework Statement

Calculate the [OH-] concentration in a 0.5 M solution of potassium fluoride (KF). Ka for
HF is 7.2 × 10−4.

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")

 

[Borek]

F^- + H₂O <-> HF + OH^-

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