Question

If 0.30 M HCOOH (weak acid) is prepared, what will be the hydronium ion concentration at equilibrium at 25

Answer 1

The equilibrium chemical reaction is

                HCOOH(aq) + H2O(l) <------------->   HCOO-(aq)    +    H3O+(aq)

I                 0.30 M                                    0                        0

C                     -x                                     +x                       +x

E                0.30-x                                    +x                      +x

Ka = [HCOO-][H+] / [HCOOH]

1.70 x 10^-4 = x^2 / (0.30-x)

x^2 + (1.7 x 10^-4)x -(0.51 x 10^-4) = 0

Solving the quadratic equation, we get the roots

x = -0.007

x = +0.007

Thus, we use x = +0.007

Thus, the hydronium ion concentration = [H3O+] = x = 0.007 M