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Acid and base dissociation constants

A weak acid HA ionizes only partially as follows:
HA ↔ H+ + A-

The equilibrium constant for this reaction will be

A number of weak acids are capable of ionization in a stepwise manner:
H2A ↔ H+ + HA-

HA- ↔ H+ + A2-

Ka1 is always numerically greater than Ka2. The overall ionization
constant will be

In case of a weak base as NH3
NH3 + H2O ↔ NH4+ + OH-

Dissociation constants for conjugate acid-base pair

Consider the dissociation constant expressions for an acid and its

conjugate base

HA + H2O ↔ H3O+ + A-

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