Final answer:
To find the base ionization constant (Kb) for oxycodone using the given pH, calculate the pOH and then use it to find [OH-]. From there, assuming x is small, use the formula Kb ≈ [OH-]²/[B], where [B] is approximated by the initial concentration, to solve for Kb.
Step-by-step explanation:
The calculation of the base ionization constant (Kb) for oxycodone, which is a weak base, can be derived from the provided pH value of the solution and its molarity. Given a pH of 10.85, the pOH can be calculated by subtracting the pH from 14 (14 - 10.85 = 3.15). The concentration of hydroxide ion ([OH-]) can be found using the formula [OH-] = 10-pOH, which for this example, is 10-3.15.
Since oxycodone is a weak base, it partially dissociates in solution, establishing an equilibrium between the undissociated base (B), the hydroxide ion (OH-), and the conjugate acid (BH+): B + H2O ⇌ BH+ + OH-. We can then employ the formula Kb = [BH+][OH-]/[B], where [B] is the initial concentration of the base minus any dissociated amount, which for weak bases, can often be approximated by the initial concentration assuming x is small.
However, to determine Kb, we need concentrations of all species at equilibrium. Assuming x is small, and because the pH is greater than 7, indicating a basic solution, we can assume that [BH+] is approximately equal to [OH-] at equilibrium due to the 1:1 stoichiometry between B and OH- in the reaction.
Therefore, if [OH-] = x and [B] ≈ original concentration, Kb ≈ x2/[B]. Substituting the known values, we'd solve for x and then for Kb. The provided information seems insufficient to complete the calculation because the concentration of [OH-] needs to be determined using the given pH first, and for full accuracy additional data regarding the percentage of ionization may be required.