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18 January, 02:31

Using the Henderson-Hasselbalch equation, calculate the percentage of an ammonia solution that would be in the ionic form at pH 9.40, assuming a pKa for the ammonium ion of 9.25.

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  1. 18 January, 02:41
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    41.45% is the precentage of the ionic form

    Explanation:

    H-H equation is used to find pH of a buffer. The formula is:

    pH = pKa + log₁₀ [X⁻] / [HX]

    Where X⁻ is the conjugate base of the weak acid, HX.

    In the ammonia buffer:

    NH₄⁺ ⇄ NH₃ + H⁺

    NH₄⁺ is the weak acid (Ionic form) and NH₃ is the conjugate base. Replacing:

    9.40 = 9.25 + log₁₀ [NH₃] / [NH₄⁺]

    1.4125 = [NH₃] / [NH₄⁺] (1)

    In a percentage, [NH₃] + [NH₄⁺] = 100 (2)

    Replacing (2) in (1):

    1.4125 = 100 - [NH₄⁺] / [NH₄⁺]

    1.4125[NH₄⁺] = 100 - [NH₄⁺]

    2.4125[NH₄⁺] = 100

    [NH₄⁺] = 41.45% is the precentage of the ionic form
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