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.

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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