17. Solving a chemistry problem

3. A sample of a solution of methylamine CH3NH2 with a volume of 20.00 ml was diluted in a volumetric flask to 100.0 ml, then 10.00 ml of the resulting solution was titrated potentiometrically with 0.1000 M HCl. Plot titration curves in pH-V and ΔpH/ΔV-V coordinates and determine the concentration (mol/l) of the stock methylamine solution using the following data:
Option 3
V(HCl), ml 12.00 15.00 17.00 17.80 18.00 18.20 18.50 19.00
pH 10.36 9.96 9.43 9.17 8.28 5.99 3.28 2.89 2.58