If the base dissociation constant Kb increases, which statement is true about pKb and base strength?

If the base dissociation constant Kb increases, which statement is true about pKb and base strength?

• A. pKb increases; base becomes weaker
• B. pKb remains unchanged
• C. pKb decreases; base becomes stronger
• D. pKb decreases; base becomes weaker

Answer: (C)

A base’s strength in water is tied to its dissociation constant Kb: a larger Kb means the base more readily accepts a proton from water, producing more OH− and thus behaving as a stronger base. The pKb is defined as the negative logarithm of Kb, pKb = -log10(Kb). When Kb increases, the logarithm increases, but the negative sign makes pKb decrease. A smaller pKb corresponds to a stronger base because it reflects a larger tendency to accept protons. Therefore, increasing Kb makes the base stronger and lowers pKb.

A base’s strength in water is tied to its dissociation constant Kb: a larger Kb means the base more readily accepts a proton from water, producing more OH− and thus behaving as a stronger base. The pKb is defined as the negative logarithm of Kb, pKb = -log10(Kb). When Kb increases, the logarithm increases, but the negative sign makes pKb decrease. A smaller pKb corresponds to a stronger base because it reflects a larger tendency to accept protons. Therefore, increasing Kb makes the base stronger and lowers pKb.