140. Solving a chemistry problem

105. The analyzed 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 N HCl solution. Determine the concentration (mol / L) of the starting methylamine solution according to the following data - table 41.
Table 41

V, ml
(HCl) 12.0 15.0 17.0 17.5 17.8 18.0 18.2 18.5 19.0
pH 10.36 9.96 9.43 9.17 8.28 5.99 3.28 2.89 2.58