The pH of a 0.25 M aqueous solution of hydrofluoric acid, HF, at 25.0°C is 2.03. What is the value of K_a for HF?

Name: The pH of a 0.25 M aqueous solution of hydrofluoric acid, HF, at 25.0°C is 2.03. What is the value of K a for HF?
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Quizplus · Accepted Answer

The pH of 2.03 indicates an [H⁺] of 0.0093 M. Using the expression for Kₐ = [H⁺][F⁻]/[HF], and assuming [F⁻] ≈ [H⁺] and [HF] ≈ 0.25 M, Kₐ = (0.0093)²/0.25 = 3.5 × 10⁻⁴.

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