A sodium hydroxide solution has a pH of 11.40. What is its [H₃O⁺]? A) 4.0 × 10⁻²⁶ M B) 4.0 × 10⁻¹² M C) 2.5 × 10⁻³ M D) 2.5 × 10¹¹ M

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Quizplus · Accepted Answer

The concentration of hydroxide ions ([OH⁻]) in a solution can be calculated using the pH value and the relationship between pH, pOH, and the ionic product of water (Kw = 1.0 × 10⁻¹⁴ at 25°C). Given a pH of 11.40, the pOH is 14 - 11.40 = 2.60. The concentration of OH⁻ ions, [OH⁻], can be found using the formula [OH⁻] = 10⁻pOH = 10⁻².⁶⁰ = 2.5 × 10⁻³ M, which is not among the provided options. However, the question asks for [H⁺] (concentration of hydrogen ions), not [OH⁻]. Using the relationship Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴, and knowing [OH⁻] = 2.5 × 10⁻³ M, we can solve for [H⁺] = Kw / [OH⁻] = (1.0 × 10⁻¹⁴) / (2.5 × 10⁻³) = 4.0 × 10⁻¹² M, which corresponds to option B.

A Sodium Hydroxide Solution Has a PH of 11