A 0.10 M imidazole solution has a pH of 6.6. To the nearest hundredth of a unit, what fraction of the molecules are in the neutral (imidazole) form? (The pKa of the imidazolium ion is 6.0.)

Answer : The fraction of the molecules in the neutral (imidazole) form are, 0.799

Explanation : Given,

pH = 6.6

Using Henderson Hesselbach equation :

Now put all the given values in this expression, we get:

    ...........(1)

Now we have to determine the fraction of the molecules are in the neutral (imidazole) form.

Fraction of neutral imidazole =

Now put the expression 1 in this expression, we get:

Fraction of neutral imidazole =

Fraction of neutral imidazole =

Fraction of neutral imidazole =

Fraction of neutral imidazole = 0.799

Thus, the fraction of the molecules in the neutral (imidazole) form are, 0.799

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