posted by AA .
40 mL of 0.1 M solution of a weak acid (adjusted to a pH of 7.75) is titrated with 0.2 M HCl to a final pH of 2.1.
Once the pH of the weak acid reaches 2.1, it is then titrated with 20 mL of 0.25 NaOH. What is the final pH of the solution?
pKa values are 2, 6, and 9.5.