The equilibrium constant kc for the reaction hf (aq) + h2o (l) h3o + (aq) + f - (aq) is 3.5 x 10-4. what is the equilibrium concentration of h3o + if the initial concentration of hf is 1.0 m?

According to the reaction equation:

Hf (aq) + H2O (l) ↔ H3O + (aq) + F (aq)

initial 1 m 0 0

-X + X + X

(1-x) X X

We assumed that [H3O+] = X

so. at eqilibrium:

Kc = [H3O] [ F] / [Hf] when we have Kc so by substitution:

3.5x10^-4 = X^2 / (1-X)

∴X^2 = 3.5x10^-4 - 3.5x10^-4 X

X^2 + 3.5x10^-4 X - 3.5x10^-4 = Zero

by solving this equation:

(X-1.9x10^-2) (X + 1.9x10^-2) = Zero

∴X = 1.9x10^-2

∴ the equilibrium constatnt of H3O = 1.9x10^-2 M