pH of 10⁻⁸ M HCl solution (in water):

At 10⁻⁸ M HCl, must include water's H⁺ from autoionization (10⁻⁷ M). Total H⁺ ≈ 10⁻⁷ + 10⁻⁸ = 1.1 × 10⁻⁷ M. pH ≈ 6.96, slightly less than 7.