Suppose that 85 mL of 0.4 M NaF and 50 mL of 0.4 M HCl are mixed.

Question

What is the K for the dominant equilibrium in terms of Ka's, Kb's, Kw etc.?

Ka of HCl

1/Ka of HCl

Ka of HF

1/Ka of HF

Kb of F-

1/Kb of F-

Kb of Cl-

1/Kb of Cl-

Kw

1/Kw

There is no reaction.

Answer 1

millimols HCl = 0.4 x 50 = 20
millimols NaF = 85 x 9.4 = 34

.......F^- + H^+ ==> HF
I.....34.....0.......0
add.........20............
C....-20...-20.......+20
E.....14....0........20

Ka for the rxn = (HF)/(H^+)(F^-)

Doesn't that look like 1/Ka of HF to you. You could use the Henderson-Hasselbalch equation and calculate the pH of the solution.