A weak electrolyte yields only a fraction of ions from its dissolved substance under the specified conditions, as illustrated by acetic acid in water.
For a neutral weak acid, unconverted molecules coexist with hydronium and the conjugate base at chemical equilibrium. The weak acid dissociation fraction describes the partition of the dissolved inventory; the acid dissociation constant describes the chemical equilibrium at fixed solvent, temperature and standard states. A single fraction is not a permanent label for every concentration: dilution can increase that fraction while the acid dissociation constant stays fixed. Calling a substance a weak electrolyte does not mean its chemical solution must be dilute.[ref]
14.3 Relative Strengths of Acids and Bases. Chemistry 2e, §14.3, Acid and Base Ionization Constants, percent-ionization discussion preceding Example 14.7
The following ideal weak electrolyte dilution law makes the distinction quantitative for a monoprotic acid. Other weak electrolytes, mixed chemical solutions and additional proton-transfer steps require their own chemical equilibrium and inventory balances.
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