A student titrates a 0.100 M solution of a monoprotic weak acid with 0.100 M NaOH
CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A student titrates a 0.100 M solution of a monoprotic weak acid with 0.100 M NaOH. The equivalence point occurs at 25.0 mL of added base and the pH recorded just beyond the steep rise is 8.6. Which of the following best explains why the pH at equivalence is greater than 7?
(a) The titrant NaOH is added in slight excess, so some strong base remains in solution.
(b) Water autoionization produces a higher concentration of OH⁻ than H₃O⁺ at 25 °C.
(c) The conjugate base of the weak acid produced at equivalence hydrolyzes with water to generate OH⁻ ions.
(d) The solution remains a buffer of HA and A⁻ at equivalence, keeping the pH slightly basic.