Question

a 25.0 mL sample of .050 M solution of aqueous trimethylamine is titrated with a .063 M solution of HCl. calculate pH the solution after 10.0 mL, 20.0 mL, 30.0 mL of acid have been added. pKb of (CH3)_3_N= 4.19 at 25 degrees C

Answer 1

First determine where the equivalence point is so you will know where you are on the titration curve with each of thes additions.
mL x M = mL x M
25.0 x 0.05 = mL x 0.063
mL = about 19 or so.
Therefore, 10 mL will be before the e.p. and you will have some base and some of its conjugate. Use the Henderson-Hasselbalch equation.

b. 20 mL will be just after the e.p. So you will have an excess of 20 mL-mL for e.p. That will be an excess of HCl

c. 30 mL is same as part b.