Question

Calculate the concentration of all species in a 0.19 M KF solution.

Please dont do it wrong its been wrong all over the internet and it makes no sense

Answer 1

  KF ---> K⁺ + F^- ; KF dissociates completely.

[K⁺]=[ F^-]= 0.19 M

               F^-            +             H₂O        =             HF          +             OH^-

INitial:   0.19 M                                               0                           

Final:     0.19-x                                                 x                            x

Ka = 7.08*10^-4 ; Kb = 10^-14/7.08*10^-4 = 1.41*10^-11 = [HF][ OH^-]/[ F^-]

or, 1.41*10^-11 = x²/0.19-x = x²/0.19            ;(as x<<0.19)

or, x = 1.64*10^-6 M

Ans: [K⁺]= 0.19 M

[F^-] = 0.19-x = 0.19 M     ;(as x<<0.19)

[HF]= [OH^- ] =1.64*10^-6 M

[H+] = 10^­14/1.64*10^-6 = 6.1*10^­-9 M