Which of the following best explains why the pH of a strong acid–strong base titration curve changes very little once a large excess of titrant base has been delivered beyond the equivalence point?
a) The conjugate base produced at the equivalence point forms a buffer with any remaining acid, so further additions of base barely change the pH.
b) Because the water generated during neutralization establishes a buffer around pH 7, extra base causes almost no pH shift.
c) The solution now contains a great excess of fully dissociated OH− ions, so additional base produces only a negligible change in their concentration and the pH approaches a limiting value.
d) Added base quickly reacts with dissolved CO₂ to form HCO3−, keeping the OH− concentration—and therefore the pH—nearly constant.