IB Chemistry - Acids and Bases

IB Chemistry home > Syllabus 2025 > Acids and Bases > Strong and weak acids and bases

Acids and bases may be described as strong or weak. In this section we look at the meaning of these terms as specifically applied to these compounds. The way that they can be differentiated by property is outlined.

Syllabus reference

Reactivity 3.1.6 - Strong and weak acids and bases differ in the extent of ionization.

  • Recognize that acid–base equilibria lie in the direction of the weaker conjugate.


  • HCl, HBr, HI, HNO3 and H2SO4 and are strong acids, and group 1 hydroxides are strong bases.
  • The distinction between strong and weak acids or bases and concentrated and dilute reagents should be covered.

Tools and links

  • Reactivity 2.3 - How would you expect the equilibrium constants of strong and weak acids to compare?
  • Reactivity 1.1 - Why does the acid strength of the hydrogen halides increase down group 17?
  • Tool 1, Inquiry 2 - What physical and chemical properties can be observed to distinguish between weak and strong acids or bases of the same concentration?

In Chapter 8.4