Ka (Acid Dissociation Constant):
Measures the strength of an acid in solution.
Specifically, it quantifies the extent to which an acid donates protons (H⁺) to water.
Kb (Base Dissociation Constant):
Measures the strength of a base in solution.
Specifically, it quantifies the extent to which a base accepts protons or produces hydroxide ions (OH⁻) in water.
Understanding Acid-Base Dissociation
Dissociation: The process in which molecules (or ionic compounds) break apart in solution to form ions.
For Acids (HA): HA⇌H++A−
For Bases (B): B+H2O⇌BH++OH−
Interpreting Ka and Kb Values
Stronger Acids: Higher Ka values; they dissociate more in solution, producing more H⁺ ions.
Weaker Acids: Lower Ka values; they dissociate less.
Stronger Bases: Higher Kb values; they dissociate more in solution, producing more OH⁻ ions.
Weaker Bases: Lower Kb values; they dissociate less.
Relationship Between Ka and Kb
Conjugate Pairs: Every acid has a conjugate base, and every base has a conjugate acid.
Relationship:
Ka×Kb=Kw where Kw is the ion-product constant for water (1.0×10−14 at 25°C).
Importance in Chemical Reactions
Predicting Direction: Ka and Kb can help predict the direction of acid-base reactions.
Equilibrium Position: Understanding the strength of acids and bases helps in determining the position of equilibrium in a reaction.
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