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5 January, 00:08

Hydrofluoric acid, hf, has a ka of 6.8 * 10-4. what are [h3o+], [f-], and [oh-] in 0.710 m hf?

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  1. 5 January, 02:48
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    [H₃O⁺] = [F⁻] = 2.2 x 10⁻² M. & [OH⁻] = 4.55 x 10⁻¹³.

    Explanation:

    For a weak acid like HF, the dissociation of HF will be:

    HF + H₂O ⇄ H₃O⁺ + F⁻.

    [H₃O⁺] = [F⁻].

    ∵ [H₃O⁺] = √Ka. C,

    Ka = 6.8 x 10⁻⁴, C = 0.710 M.

    ∴ [H₃O⁺] = √Ka. C = √ (6.8 x 10⁻⁴) (0.710) = 2.197 x 10⁻² M ≅ 2.2 x 10⁻² M.

    ∴ [H₃O⁺] = [F⁻] = 2.2 x 10⁻² M.

    ∵ [H₃O⁺][OH⁻] = 10⁻¹⁴.

    ∴ [OH⁻] = 10⁻¹⁴/[H₃O⁺] = 10⁻¹⁴ / (2.2 x 10⁻²) = 4.55 x 10⁻¹³.
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