7. The pKa of cocaine is 8.6. At what pHs do you expect each of the structures shown above? Recall pKa is the log of Ka (ionization constant of the weak acid). The larger the pKa, the weaker the acid, the stronger the conjugate base. Which structure will be more soluble in aqueous solutions? Which structure will be more soluble in organic solvents? 8. Use the Henderson-Hasselbach equation to explain the sentence: At a pH at least two units away from the pKa, the drug will be >99% either in the neutral form or ion form. Recall the equation: pH=pKa+log[acid][base]