Final answer:
The pKb value of quinoline is 8.77, which shows its strength as a base. This value allows calculation of its conjugate acid's pKa using pKa + pKb = pKw.
Step-by-step explanation:
The pKb value of quinoline is a measure of its basicity in solution. The relationship between pKa and pKb is given by the equation pKa + pKb = pKw, where pKw is the ion product constant for water, which is equal to 14.00 at 25°C. For the quinoline base, its conjugate acid is the pyridinium ion, and the pKa for the pyridinium ion can be calculated using the pKb of quinoline.
Given the pKb value of 8.77, we can use the relationship to find the pKa of the pyridinium ion: pKa = pKw - pKb = 14.00 - 8.77 = 5.23. With this pKa value, it is possible to utilize the Henderson-Hasselbalch approximation to relate the concentrations of the acid and base forms of quinoline in a buffered solution.
Knowing one of the four quantities (Ka, pKa, Kb, or pKb), the other three can be calculated. Thus, having the pKb, we can find all related acid-base equilibria information for the substance in question.