Will the pH at the equivalence point of the 50 mL titration of 0.10 M HCl be the same, more, or less than the pH at the equivalence point of the 50 mL titration of 0.10 M acetic acid?

When equivalence point is achieved the acid or base is completely neutralized, but its salt (conjugate acid or base) can alter the pH of the solution. In the comparison of two different acidic or basic species, their conjugate is evaluated. If the base dissociation coefficient (Kb) of one conjugate base is greater than other, then the pH change due to it will be more basic.

The neutralization of HCl can be given as

HCl + OH⁻ -------------- > H₂O + Cl⁻

Here Cl⁻ is the remaining ion at the equivalence point, and it is the conjugate base of HCl. It has a Kb value of 1.0 X 10⁻²⁰ (that is why it is not considered basic).

The neutralization of acetic acid is given as

CH₃COOH + OH⁻ -------------- > H₂O + CH₃COO⁻

Here CH₃COO⁻ is the remaining ion at the equivalence point, and it is the conjugate base of acetic acid. Its Kb value is 5.6 X 10⁻¹⁰, which is higher than the Kb value of Cl⁻. As the amount of HCl and acetic acid is the same, so the solution containing chloride ions will have a lower pH than the solution containing acetate ions.