Question

Calculate the concentration of all species present and the pH of a 0.019-M HF solution. Ka for HF is 7.2 x 10-4 a (H+) = [F-]= [HF] = [OH-]= Submit

Answer 1

given, weak acid HF Initial concentration of HF = 0.019 equilibrium constant K of HF = 7.2x104 equilibrium constant K of HF = 0.00072 M H Io 0 Construct ICE table : reaction Initial(M) Change(M) Equilibrium(M) Equilibrium expression: HE 0.0190 -X 0.0190-X + F 0 +x X +x X Ka = [H+][F-] [HF] [x][x] 0.000720 = 0.0190-X x + 0.0007200 X - 0.00001368 = 0 By solving the above quadratic equation, we get x = H* = 0.00336 M

M concentration of H+ in the solution = x = 0.00336 concentration of H+ in the solution = x = 3.36x10 Concentration of the F- = x = 0.00336 M Concentration of the F- = x= 3.36x10 Concentration of HF = 0.0190-x = 0.0190 -0.00336 Concentration of HF = 0.01564 M Concentration of HF = 1.56x102 M Calculating concentration of [OH-1: [ H+ ] = 0.00336 M [ H+ ][ OH] = 1.0x10-14 1.0x10-14 [OH-] = [H+ ] 1.0x10-14 [OH-] = [ 0.00336 ] 2.98x10-12 M [OH-] = Calculating pH: with [H] = 0.00336 M pH = -log [H] pH = -log [ 0.00336 ] pH = 2.47