APFIVE The table below presents data for the equilibrium of a weak base, B, that has an initial concentration of 0.20 M and a base-dissociation constant, $$K_b$$, of $$1 \times 10^{-6}$$. Which of the following conclusions is best supported by the data?
| Species | Concentration (M) |
|---|---|
| B (initial) | 0.20 |
| OH⁻ (equilibrium) | $$1.4 \times 10^{-3}$$ |
| BH⁺ (equilibrium) | $$1.4 \times 10^{-3}$$ |
| B (equilibrium) | ≈ 0.1986 |
Although it might seem at first glance that the presence of any measurable hydroxide ion concentration would imply substantial ionization, the fact that only about 0.7% (approximately $$\frac{1.4 \times 10^{-3}}{0.20} \times 100$$) of the base ionizes is in perfect agreement with the low $$K_b$$ value, thereby confirming the expected limited ionization for a weak base.
The data indicate that nearly all of the base is ionized, as shown by the significant hydroxide ion concentration.
The equilibrium evidence implies that the weak base behaves similarly to a strong base, since the generated hydroxide ion concentration is almost equal to the initial base concentration.
The small degree of ionization—less than 1%—is consistent with the low $$K_b$$ value, demonstrating that only a minor fraction of the base reacts to form hydroxide ions.
Question Leaderboard
Not enough data yet to show leaderboard.