A base is considered strong if it dissociates completely in water to produce a high concentration of hydroxide ions, while a weak base only partially dissociates and produces fewer hydroxide ions in solution.
Key Differences
- Strong base: Fully dissociates in water, often includes Group 1 or 2 metal hydroxides such as sodium hydroxide (NaOH) and potassium hydroxide (KOH).
- Weak base: Partially dissociates, examples include ammonia (NH3), pyridine, and other organic compounds containing nitrogen.
How to Tell Strength
- Check if the base is a hydroxide of a Group 1 or 2 metal—these are typically strong bases.
- Measure how fully the base dissociates in water; strong bases produce lots of OH^- ions.
- Look at the base's conjugate acid: a strong base usually has a weak conjugate acid.
- For organic bases, negatively charged species (e.g., carbanions, alkoxides, amide ions) are generally stronger bases than those with resonance stabilization or higher electronegative atoms.
- The value of KbK_bKb (base dissociation constant) reflects base strength—a larger KbK_bKb or smaller pKbpK_bpKb indicates a stronger base.
Example Table
Base| Strong/Weak| Why?
---|---|---
NaOH| Strong| Fully dissociates; Group 1 hydroxide610
KOH| Strong| Fully dissociates; Group 1 hydroxide610
NH3| Weak| Partially dissociates; organic base26
Ca(OH)2| Weak| Only partially dissociates610
Pyridine| Weak| Partially dissociates; organic base2
Summary
Strong bases dissociate completely in water and are usually Group 1 or 2 hydroxides. Weak bases only partially dissociate, often are organic, and their strength can be inferred by the stability of their conjugate acids and the KbK_bKb value.
