8.7 pH and pKa

Explain the relationship between the predominant form of a weak acid or base in solution at a given pH and the pKa of the conjugate acid or the pKb of the conjugate base.

• The protonation state of an acid or base (i. the relative concentrations of HA and A−) can e., be predicted by comparing the pH of a solution to the pKa of the acid in that solution. When solution pH < acid pKa, the acid form has a higher concentration than the base form. When solution pH > acid pKa, the base form has a higher concentration than the acid form.
• Acid-base indicators are substances that exhibit different properties (such as color) in their protonated versus deprotonated state, making that property respond to the pH of a solution.
• T o ensure accurate results in a titration experiment, acid-base indicators should be selected that have a pKa close to the pH at the equivalence point.