Unlike Ka, the percent ionization of a weak acid typically changes when:

1. Ka is a constant at a given temperature and does not depend on how much acid you started with. 2. Percent ionisation is a different measure, being the fraction of acid that has ionised. 3. Unlike the Ka value, the percent ionization of a weak acid varies with the initial concentration of acid. 4. It typically decreases as concentration increases. 5. A dilute weak acid is therefore proportionally more ionised than a concentrated one. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 14 'Acid-Base Equilibria', sections 14.1-14.7_