Which of the following describes a weak base in terms of its Ka value?

A weak base is characterized by its limited ability to accept protons (H⁺), which is reflected in its dissociation constant (Kb) or indirectly in terms of Ka (the acid dissociation constant of its conjugate acid). For weak bases, the Ka value is relatively low because they do not dissociate significantly in solution.

The correct description of a weak base is a low Ka value, indicating that the base has a lesser tendency to ionize and produce hydroxide ions in solution. Consequently, a weak base would produce a conjugate acid with a high pKa value, since pKa is inversely related to Ka (as pKa = -log(Ka)). Therefore, a weak base, with its low Ka, correlates to a high pKa for its conjugate acid.

This alignment denotes that while a weak base does have a low affinity for protons, its conjugate acid is relatively stable and tends not to release protons easily, signifying a higher pKa. The concept of comparing the strength of bases (and their resulting acids) is essential in understanding acid-base chemistry and reactivity in various solutions.