In a strong acid–base titration, 25.0 mL of 0.100 M NaOH is titrated with 0.100 M HCl. What is the pH at the equivalence point?

• A. About 7.00
• B. About 1.00
• C. About 3.00
• D. About 9.00

Answer: (A)

In a strong acid–base titration, the equivalence point occurs when the moles of acid equal the moles of base, so the reaction mixture contains only the salt formed by the two reacting species and water. For a strong acid and a strong base, the resulting salt (sodium chloride) does not hydrolyze in water, which means the solution behaves like neutral water. At 25°C, this gives a pH of about 7.

Here, the base provides 0.025 L × 0.100 M = 2.5×10^-3 moles of NaOH. At equivalence, the same amount of HCl is added, so the final solution contains NaCl in water with no excess H+ or OH−. The total volume is 0.050 L, and since there’s no excess acid or base to shift the balance, the pH remains neutral, about 7.00.