Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
The base-ionization constant (Kb) quantifies the strength of a base in a solution. It is the equilibrium constant for the dissociation of a base into its conjugate acid and hydroxide ion.
5 Must Know Facts For Your Next Test
Kb is used to compare the strengths of different bases; a higher Kb value indicates a stronger base.
The formula for Kb is $K_b = \frac{[BH^+][OH^-]}{[B]}$, where [BH+] is the concentration of the conjugate acid, [OH-] is the concentration of hydroxide ions, and [B] is the concentration of the base.
Bases with Kb values greater than $1 \times 10^{-2}$ are considered strong bases, while those with lower values are weak bases.
Kb values can be used to calculate pOH and subsequently pH, important for understanding the acidity or basicity of solutions.
There is an inverse relationship between Ka (acid dissociation constant) and Kb for conjugate acid-base pairs: $K_a \times K_b = K_w$ (where $K_w$ is the ion-product constant for water).
Review Questions
Related terms
Acid Dissociation Constant (Ka): A quantitative measure of the strength of an acid in solution; it represents how completely an acid dissociates into its ions.
A measure of hydroxide ion concentration; calculated as $pOH = -\log[OH^-]$.
Ion-product Constant for Water (Kw): $Kw$ represents the product of hydrogen ion concentration and hydroxide ion concentration in water at a specific temperature, typically $1.0 \times 10^{-14}$ at room temperature.