For a titration of 0.1 M HCl with 0.1 M NaOH, what is the pH at the equivalence point at 25°C?

• A. pH = 7 at the equivalence point.
• B. pH < 7 at the equivalence point.
• C. pH > 7 at the equivalence point.
• D. pH cannot be determined from this data.

Answer: (A)

In a titration between a strong acid and a strong base, the equivalence point leaves the solution containing only water and the spectator ions (Na+ and Cl−). These ions do not hydrolyze to alter the pH, so the solution is effectively neutral. At 25°C, neutral water has pH 7, and this is why the equivalence point for a strong acid–strong base titration is pH 7 regardless of the concentrations (as long as both reactants are strong). So the pH at the equivalence point here is 7.