Answer is: the hydrogen
ion concentration is 2.5·10⁻⁷ M.<span>
[OH</span>⁻] = 4·10⁻⁸<span> mol/L, equilibrium concentration of hydroxide
anion.
[H</span>⁺]
is the equilibrium concentration<span> of hydrogen ions.
[OH</span>⁻] ·
[H⁺] = 10⁻¹⁴ mol²/L², ionicproduct of water on room temperature.<span>
[H</span>⁺] =
10⁻¹⁴ mol²/L² ÷ 4·10⁻⁸ mol/L.<span>
[H</span>⁺] = 2,5·10⁻⁷ mol/L = 0,00000025 mol/L.