In an experiment, a 45.0 mL sample of 0.15 M triethylamine, (CH3)3N (aq), was placed in a flask and titrated to the equivalence point and beyond using 0.10 M HNO3(aq), according to the balanced equation below: (CH3)3N (aq) + HNO3(aq) →(CH3)3NH+(aq) + NO3−(aq)

Calculate the pH after the following volumes of HNO3have been added. The Kb of triethylamine is equal to 6.4 × 10-5.

1) 0.0 mL
2) 36.0 mL
3) 67.5 mL
4) 70.0 mL