What is the pH of a solution of 0.15 M formic acid?

A 0.015 M solution of a monoprotic acid is 0.92% ionized. Calculate the ionization constant for the acid.?

• An aqueous solution of barium hydroxide has a pH of 9.78 at 25*C. Calculate the concentration of the base. Could someone please explain these two questions to me. Thanks.

• Answer:

  pH = 9.78 which mean the pOH = 14 - 9.78 = 4.22 This means the [OH] = 1x10^-4.22 or more conventionally, [OH-] = 6.025x10^-5 M Since barium hydroxide is Ba(OH)2 you get 2 moles of OH for each mole of Ba(OH)2. So the concentration of the base will be 1/2 6.02x10^-5 = 3x10^-5 M HA ---> H+ + A- Ka = [H+][A-]/[HA] If you start with 0.015 M and it ionizes 0.92% then you get 0.000138 M H+ and A-, leaving 0.0149 HA Substituting these values in the equation for Ka you get Ka = (0.000138)^2/0.0149 Ka = 1.28x10^-6 M