Question

Maleic acid (H2M) is a diprotic acid with Ka1 = 1.3x10-2 and Ka2 = 8.5x10-7. I am titrating 25.00 mL of a 0.350 M aqueous solution of maleic acid with a 0.250 M aqueous solution of sodium hydroxide (NaOH (aq)). Calculate the pH of the solution after addition of 45.77 mL of NaOH (aq).

Answer 1

Since this ia a weak acid(Maleic acid) and a strong base(NaOH) titration all the H+ ions available will be used up by the OH- ions. Concentration of [H+] after first dissociation is-

this is after the first dissociation

the concentration of OH- after dissociation is

therefore alot of [OH-] ions are left.

These will be used up in the second dissociation of the maleic acid because we sill have [H+] ions left

this much [H+] ion is possible to be released but only 0.00606 will be used because only tihs much [OH-] ions are left. the rest of the maleic acid will be in a equilibrium with the water with a Ka2= 8.5x10^-7

therefore the pH will be

Therefore the pH=6.506 which is slightly acedic.