Final answer:
The pH at the endpoint of the titration cannot be determined because the concentration of the acid becomes zero, resulting in an undefined pH value.
Step-by-step explanation:
The pH at the endpoint of the titration can be determined using the Henderson-Hasselbalch equation, which relates the pH of a weak acid solution to its pKa and the ratio of the concentrations of the acid and its conjugate base.
In this case, the weak acid is HA and its conjugate base is A-. The pKa of HA is given as 7.0×10⁻⁶. Since the titration is with a strong base (NaOH), the weak acid HA will be completely converted to its conjugate base A-. Therefore, at the endpoint, the concentration of HA will be zero and the concentration of A- will be the same as the concentration of NaOH.
Using the zenderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Since [A-] = [NaOH] = 0.35 M and [HA] = 0 M at the endpoint
pH = 7.0×10⁻⁶ + log(0.35/0)
Since the logarithm of zero is undefined, the pH at the endpoint is also undefined. This means that the solution will not have a well-defined pH at the endpoint of the titration.