Final answer:
Novocaine is acidic due to procaine being a weak base. The pH, [H3O+], and [OH-] of a novocaine solution can be calculated from its molarity, derived from the mass percentage and density, and its ionization constant.
Step-by-step explanation:
Nocaine, which contains the base procaine, is a salt formed from procaine and hydrochloric acid. The ionization constant for procaine is 7 x 10^-6, indicating that procaine is a weak base. Solutions of salts of weak bases and strong acids, like novocaine, tend to be acidic because the anions of the weak base are hydrolyzed in water, increasing the hydrogen ion concentration.
To determine the concentration of hydrogen ions ([H3O+]), hydroxide ions ([OH-]), and the pH of a 2.0% novocaine solution, we use the mass percentage and density to find the molarity. Assuming the density of the solution is 1.0 g/mL, a 2.0% solution by mass corresponds to 20 g of novocaine per liter of solution, which equates to the molarity given the molecular weight of novocaine.
Once the molarity is known, the dissociation of novocaine in water can be represented with an equilibrium expression using the procaine ionization constant to solve for [H3O+]. With [H3O+], we can calculate the pH of the solution and use the Kw (ion product constant for water) to find [OH-].