The acid dissociation constant (Ka) quantifies the extent to which a weak acid dissociates in solution. A higher Ka value indicates a stronger acid (more dissociation), while a lower Ka value indicates a weaker acid (less dissociation). Strong acids completely dissociate and thus don’t have a Ka value (it’s considered very large).
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Calculation:
For the generic weak acid HA:
HA ⇌ H⁺ + A⁻
The acid dissociation constant is defined as:
Ka = [H⁺][A⁻] / [HA]
Where:
- [H⁺] is the concentration of hydrogen ions (often expressed as pH).
- [A⁻] is the concentration of the conjugate base.
- [HA] is the concentration of the undissociated acid.
