Question

The Ka for hydrofluoric acid is     1.5×10−11. What is Ka for the fluoride ion?

The Ka for hydrofluoric acid is     1.5×10−11. What is Ka for the fluoride ion?

Answer 1

Well....`K_w=K_aK_b`

Explanation:

Alternatively....`log_(10)K_w=log_10K_a+log_10K_b`

...or `pK_w=14=pK_a+pK_b`

And so if `K_a(HF)=1.5xx10^-11`...then `pK_a=-log_10(1.5xx10^-11)=10.8`...and thus `pK_b` for the conjugate base is `14-10.8=3.2`...`K_b=10^(-3.2)=6.31xx10^-4`.

And note it is an experimental FACT that fluoride salts GIVE basic solutions....