here the solution is 0.015 M HCl so we have HCl --> H+ + Cl- now, [H+] = 0.0015 M so we have pH = -log[H+] = - log [ 0.0015] = 2.82 and [H3O +] = [H2O][H+] = 0.0015 * 1.4 x 10-14 = 2.1 x 10-17 M Solution here the solution is 0.015 M HCl so we have HCl --> H+ + Cl- now, [H+] = 0.0015 M so we have pH = -log[H+] = - log [ 0.0015] = 2.82 and [H3O +] = [H2O][H+] = 0.0015 * 1.4 x 10-14 = 2.1 x 10-17 M.