[skibum143]

0.2 moles of NaF are added to 4.0L of pure water. What is pH?

I know 0.2moles/4L = [0.5]
But I can't figure out what the equation is:
NaF + H2O -> HF + OH-

But when I get the concentration of OH- using the Ka, the answer is wrong, and when I try to follow up with what happens to the HF (HF + H2O -> H3O+ + F-), the value I get for H3O+ using the Ka to get pH is also wrong. I don't know how to properly combine the [H3O+] and the [OH-]

Thanks

[Borek]

To get OH^- you need to use Kb.