Final answer:
The percent ionization of a weak acid is inversely related to its concentration. A weak acid that is 4.2% ionized at 0.10 M will have a lower percent ionization at 1.0 M.
Step-by-step explanation:
The percent ionization of a weak acid decreases with an increase in concentration. The percent ionization is calculated by comparing the concentration of ionized acid to the initial concentration of the acid, and multiplying by 100 to get a percentage. Using the given acid dissociation constant (Ka) and the initial concentration, one can calculate the equilibrium concentrations of the products and reactants and thereafter the percent ionization.
For a 0.10 M solution of a weak acid with a given Ka = 1.8 x 10-4, if it is 4.2% ionized, the ionization would be less when the concentration of the solution is increased to 1.0 M. The relationship between the percent ionization and concentration is inverse, as a higher concentration of the acid means a smaller fraction will ionize, given that the acid is weak and does not fully dissociate in solution.