Q. The hydrogen ion concentration of a 10⁻⁸ M HCl aqueous solution at 298 K (Kw = 10⁻¹⁴) is :
A) 1.0525 × 10⁻⁶ M
B) 1.0525 × 10⁻⁷ M
C) 8.525 × 10⁻⁸ M
D) 1.0525 × 10⁻⁸ M
Explanation
[Solution from source] At 10⁻⁸ M the acid's H⁺ is smaller than that from water, so both must be counted: x(x − 10⁻⁸) = 10⁻¹⁴. Solving, x = [10⁻⁸ + √(10⁻¹⁶ + 4 × 10⁻¹⁴)]/2 ≈ 1.05 × 10⁻⁷ M (pH ≈ 6.98). Taking [H⁺] = 10⁻⁸ M would make an acid solution basic (pH 8). Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.