Question

In: Chemistry

What is the pOH of 0.0042 M LiF? Ka = 7.1 x 10-4 7.39 11.24 6.61...

What is the pOH of 0.0042 M LiF?

Ka = 7.1 x 10-4

7.39
11.24
6.61
2.76
9.15

Solutions

Expert Solution

LiF -----------> F- + Li+

           F- + H2O------------> HF + OH^-

I        0.0042                    0        0

C      -x                             +x       +x

E     0.0042-x                    +x        +x

      Kb = Kw/Ka = 1*10^-14/7.1*10^-4 = 1.4*10^-11

   Kb = [HF][OH-]/[F-]

1.4*10^-11 = x*x/0.0042-x

1.4*10^-11*(0.0042-x) = x^2

   x = 2.42*10^-7

[OH-] = x = 2.42*10^-7M

POH = -log[OH-]

        = -log2.42*10^-7    = 6.6161 >>>>>>answer


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