Chemistry
Chemistry
Problem
A solution of weak acid HA is being titrated with 0.1 M NaOH solution. End point is reached on addition of x mL of NaOH. To the above solution, mL of 0.10 M HCl is added further. pH of the resulting solution was found to be 5.3. Determine pH at the end point if initial concentration of weak acid was 0.10 M.Intuitive explanation
This problem hinges on recognizing that after the titration endpoint, adding HCl creates a buffer—a mixture of the conjugate base (A⁻) and the newly formed weak acid (HA). The pH at the endpoint itself is determined by the hydrolysis of A⁻ alone, but the pH after adding HCl gives you the value through the Henderson-Hasselbalch equation. Once you know , you can calculate the endpoint pH where only A⁻ is present.
Intuitive explanation
This problem hinges on recognizing that after the titration endpoint, adding HCl creates a buffer—a mixture of the conjugate base (A⁻) and the newly formed weak acid (HA). The pH at the endpoint itself is determined by the hydrolysis of A⁻ alone, but the pH after adding HCl gives you the value through the Henderson-Hasselbalch equation. Once you know , you can calculate the endpoint pH where only A⁻ is present.