Final answer:
Continuing to add NaOH after the endpoint will cause a rapid increase in the pH of the solution because excess hydroxide ions from the NaOH will be present, but this rise in pH will level off at the pH of the NaOH solution itself.
Step-by-step explanation:
If you keep adding NaOH to a solution after the end point, the pH of the solution increases. Initially, at the equivalence point, the pH is neutral because the amount of acid equals the amount of base in the solution. Continuing to add NaOH, a strong base, will cause more hydroxide ions to be present in the solution, increasing the pH. Near the equivalence point, this increase in pH can be quite rapid as most of the H+ ions from the acid have been neutralized and fewer molecules are available to react with the additional base. Eventually, the pH levels off at a value of about 13.30, which is the pH of a 0.20 M NaOH solution.