Calculate the the molar concentration of H3O+ ions and the pH of the following solutions:
a) 25.0 cm3 of 0.144 M HCl(aq) was added to 25.0 cm3 of 0.125 M NaOH(aq)
b) 25.0 cm3 of 0.15 M HCl(aq) was added to 35.0 cm3 of 0.15 M KOH(aq)
c) 21.2 cm3 of 0.22 M HNO3(aq) was added to 10.0 cm3 of 0.30 M NaOH(aq)
pH = -log[H3O+] Handerson - Hasselbach eqn.
The Attempt at a Solution
I have only been able to solve part a)
I did that by multiplying the molairty of the strong acid/base by the total volume
then: [H3O+] = [HCl] - [NaOH] = 9.5 x 10-3mol
then took the negative log of that number to find the pH = 2.0
which are the correct answers, but when I do that process for part b) and c) which are also strong acid/base combos, the answers are no where near correct.
Any help will be appreciated.