Chemistry 12 · Chemistry · Lesson 4.2
The strengths of acids and bases
- Level
- Grade 12
- Reading time
- 12 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Strong versus weak; degree of ionization.
What is the difference between strong and weak acids?
Short answer
A strong acid ionizes completely in water, releasing all of its hydrogen ions, while a weak acid ionizes only partially, so most of it stays as intact molecules in equilibrium with its ions. Strength refers to the degree of ionization, not concentration: a dilute strong acid is still strong, and a concentrated weak acid is still weak.
Concept preview
What you will be able to do
- 01Distinguish strong from weak acids and bases
- 02Calculate a percent ionization
- 03Explain why strength and concentration are independent
The words strong and weak have precise meanings in acid-base chemistry, and they refer only to how completely a substance ionizes. A strong acid, such as hydrochloric acid, ionizes essentially completely in water: virtually every molecule donates its proton, so the reaction is written with a single arrow, . A weak acid, such as the acetic acid in vinegar, ionizes only slightly: most molecules stay intact, and only a small fraction release their proton, so the process is an equilibrium written with a double harpoon, .
School Plan
The strengths of acids and bases
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Related topics
Frequently asked questions
- Is a concentrated acid the same as a strong acid?
- No. Strength is the degree of ionization; concentration is how much acid is dissolved. A concentrated weak acid is still weak.
- Why do weak acids reach equilibrium?
- Because they ionize only partially, so intact molecules and their ions coexist in a dynamic equilibrium described by Ka.