Acids and Bases
Base Dissociation Constant
The base dissociation constant, $ K_b $ , is a measure of the strength of a base in aqueous solution. It represents the equilibrium constant for the reaction of a base with water to produce the conjugate acid and hydroxide ions.
For a generic weak base, B, reacting with water:
$$ B(aq) + H_2O(l) \rightleftharpoons BH^+(aq) + OH^-(aq) $$
The expression for $ K_b $ is:
$$ K_b = \frac{[BH^+]][OH^-]]}{[B]]} $$
where:
- $ [BH^+]] $ is the concentration of the conjugate acid
- $ [OH^-]] $ is the concentration of hydroxide ions
- $ [B]] $ is the concentration of the base
A larger $ K_b $ value indicates a stronger base. A stronger base will dissociate more completely in water, producing a higher concentration of hydroxide ions.
Relationship between $ K_a $ and $ K_b $ This is crucial for understanding the relationship between conjugate acid-base pairs.
Calculating $ pK_b $ This explains how to calculate $ pK_b $ from $ K_b $ , analogous to $ pH $ and $ pK_a $ .
Weak Base Equilibria Calculations This will cover examples and practice problems involving calculating $ [OH^-]] $ , $ [BH^+]] $ , and $ [B]] $ at equilibrium, given $ K_b $ and initial concentration.
Buffer Solutions This would discuss how weak bases can be used to make buffer solutions which resist changes in pH when small amounts of acid or base are added. This would link to Relationship between $ K_a $ and $ K_b $ and Weak Base Equilibria Calculations]].