Thus, with pH = -log concentration of H+, the 1 M solution of HCl will give the pH of -log 1 or 0 (Zero), because 10 ^0 = 1. The pH of 1 M hydrochloric acid is zero. The reason is that pH is defined as negative 1 times the log base 10 of [H+], or the proton concentration in moles per liter.