AP Chemistry Flashcards: Weak Acid and Base Equilibria
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 16 cards to help you master important concepts.
How is pKa calculated?
pKa is the negative base-10 logarithm of the acid dissociation constant (Ka), calculated as pKa = -log(Ka).
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How is pKa calculated?
pKa is the negative base-10 logarithm of the acid dissociation constant (Ka), calculated as pKa = -log(Ka).
In a weak acid solution, why is the hydronium ion concentration [H3O+] much less than the initial acid concentration?
This occurs because weak acids only partially ionize in water, meaning the equilibrium lies far to the left, favoring the un-ionized acid molecules.
How can you determine the pH of a weak base solution from its initial concentration and pKb?
First, use the initial concentration and pKb (or Kb) to calculate the equilibrium [OH-]. Then, calculate pOH and use the relationship pH + pOH = 14 to find the pH.
What is percent ionization?
Percent ionization is the percentage of a weak acid or weak base molecules that have ionized in solution at equilibrium.
What two pieces of information are needed to determine the pH of a weak acid solution?
To determine the pH of a weak acid solution, you need the initial concentration of the acid and its pKa (or Ka).
What does the acid dissociation constant, Ka, represent?
Ka is the equilibrium constant for the reaction of a weak acid with water, indicating the extent of its ionization.
What is a weak acid?
A weak acid is a substance that reacts with water to produce hydronium ions, but only a small percentage of its molecules ionize.
What is a weak base?
A weak base is a substance that reacts with water to produce hydroxide ions, but only a small percentage of its molecules ionize.
What major species are in equilibrium in a solution of a monoprotic weak acid (HA)?
The species in equilibrium are the un-ionized acid (HA), its conjugate base (A-), and hydronium ions (H3O+).
How is pKb calculated?
pKb is the negative base-10 logarithm of the base dissociation constant (Kb), calculated as pKb = -log(Kb).
What does the base dissociation constant, Kb, represent?
Kb is the equilibrium constant for the reaction of a weak base with water, indicating the extent to which the base accepts a proton from water.
What is the mathematical relationship between Ka and Kb for any conjugate acid-base pair?
For any conjugate acid-base pair, the product of their dissociation constants is equal to the ion-product constant for water: Ka × Kb = Kw.
Describe the equilibrium present in a solution of a weak base.
A weak base solution involves a dynamic equilibrium between the un-ionized base, water, the conjugate acid of the base, and hydroxide ions.
What information can be used to calculate the percent ionization of a weak acid or base?
Percent ionization can be calculated from its pKa (or pKb) and initial concentration, or from the initial concentration and the equilibrium concentration of any species.
What is the relationship between pKa and pKb for any conjugate acid-base pair?
The sum of the pKa of a weak acid and the pKb of its conjugate base is equal to pKw, which is 14 at 25°C (pKa + pKb = pKw).
In a solution of a weak base, how are pH and pOH related to the concentrations of the species present?
The pOH is determined by the equilibrium concentration of OH-, and the pH is then found using pH = 14 - pOH. The concentrations of the base and its conjugate acid are related by Kb.