Problem

Solutions For An Introduction to Medicinal Chemistry Chapter 11 Problem 5Q

Step-by-Step Solution

Solution 1

The power of dissociation of an acid or base refers to the negative of the logarithm of their equilibrium dissociation constant. Hence, if the equilibrium constant for a dissociation reaction is K_a:

The power of hydrogen, or pH, relative to the pK of a solution will determine the extent of ionization of an acidic or basic solution. The extent of ionization of histamine will depend upon the pH of its surrounding solution.

Step #2 of 3

(a)

If the pH value of a histamine solution is 5.74, it is at equilibrium in its dissociation reaction. Hence, the ratio of ionized to unionized histamine will be 1:1.

Step #3 of 3

(b)

If the pH value of histamine solution is 7.4, which means that the solution is more basic than pK_a of histamine. Hence, there will be a higher degree of unionized histamine relative to ionized histamine. As per the Henderson-Hasslebach equation: