114. Solving a chemistry problem

6. The analyzed solution of methylamine CH3NH2 with a volume of 20.0 ml was diluted in a volumetric flask to 100.0 ml. Construct potentiometric titration curves in the coordinates pH-V and ΔpH / ΔV - V and determine the concentration of methylamine (mol / l), if the following results were obtained when titrating 20.0 ml of the prepared solution of 0.2000 N HCl:

V(HCl), ml 10.0 12.0 14.0 14.5 14.9 15.0 15.1 15.5 16.0
pH 10.42 10.12 9.56 9.28 8.42 5.90 3.24 2.55 2.25