Question

What happens if I try to make a pH 6 buffer by diluting 0.100 M HCL (aq) with water .

Answer 1

You can dilute 0.1 M HCl (pH = 1) to make pH = 6; however, that will not be a buffer because you have nothing to take up H^+ or OH^- when added to the "so-called" buffer you have prepared.