Stop fruitless discussions and start calculations.

To 10 cm

^{3} of 0.1 M acetic acid add successively 10 times 1 cm

^{3} of 0.1 M NaOH and for each solution calculate the pH using the Henderson-Hasselbach equation (this is an approximate method, but sufficient to understand the phenomenon).

Use the chart from

https://www.chembuddy.com/?left=buffers&right=buffer-capacity. Add an additional vertical volume axis on the graph (next to the buffer capacity 0.01, 0.02, etc., add the volumes of 1 cm

^{3}, 2 cm

^{3} ...) and add your points from the calculations (or measurements). The pH value of 0.1 M acetic acid is 2.89, pH value of 0.1 M sodium acetate is 8.89. In this case, a good range of buffer operation is considered to be the range of pH + -1 to the pKa value of the acid, i.e. from 3.77 to 5.77, which for this particular example will mean the amount of added NaOH from 2 to 8 cm

^{3}, so at 7 out of 10 titration measurement points we will be observed a pronounced buffering effect.