A monoprotic weak acid HA has Ka=4.5×10−4 at 25 °C. Three separate solutions are prepared with initial concentrations of HA equal to 0.001 M, 0.050 M, and 1.0 M.
(a) For each initial concentration, predict whether the assumption that the equilibrium concentration of HA is essentially equal to its initial concentration is likely to be valid. Justify each prediction qualitatively, citing appropriate chemical reasoning.
(b) Choose the concentration for which this assumption is least certain. Calculate the percent ionization for that solution to quantitatively support your prediction from part (a).
(c) Without doing further calculations, explain how the percent ionization for any one of these solutions would change if Ka increased while the initial concentration remained constant. Provide reasoning based on equilibrium principles.