CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 0.10 M solution of weak acid X is 1.0 % ionized, whereas an equally concentrated solution of weak acid Y is 5.0 % ionized under identical conditions. Which statement about their acid-dissociation constants is most accurate?
(a) Ka(X) equals Ka(Y) because both acids have the same initial molarity, and Ka depends on concentration rather than percent ionization.
(b) Ka(X) is larger than Ka(Y) because, at equal concentration, a lower percent ionization corresponds to a larger equilibrium constant.
(c) Ka(Y) is larger than Ka(X) because a greater fraction of Y molecules dissociate.
(d) Ka(Y) is only about five times larger than Ka(X) because Ka≈αC for dilute solutions, making it directly proportional to percent ionization.